From Dna To Protein: How Cells Readthe Genome

Front 1

Sources of DNA variation

Back 1

DNA mismatches during replication
Spontaneous mutations (depurination adn deamination)
Induced mutations (thymine dimers)
Transposons and transposase

Front 2

DNA only transposons do not require

Back 2

sequence similarity to be inserted in target site

Front 3

RNA intermediate

Back 3

retrotransposons

Front 4

Retrotransposons

Back 4

host polymerase makes RNA from retrotransposon DNA

Front 5

Reverse transcriptase is encoded by

Back 5

retrotransposon; makes a DNA copy from RNA

Front 6

Alu sequence

Back 6

retrotransposon
1 million copies in genome
relatively recent in evolutionary time.

Front 7

DNA only transposons do not require

Back 7

Sequence similarity to be inserted in target site.

Front 8

Viruses are

Back 8

mobile genetic elements

Front 9

Retrovirsues are integrated into host as a

Back 9

provirus

Front 10

polymerase chain reaction (PCR) amplify

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rare sequences

Front 11

Temperature resistant DNA polymerase

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Taq polymerase

Front 12

In 20 cycles the DNA is amplified more thn a

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million fold

Front 13

Amplifies known sequences by using specific primers to

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guide amplification

Front 14

gene expression varies - the first point of control is

Back 14

transcriptional

Front 15

Transcription produces an RNA complementary to

Back 15

one strand of DNA

Front 16

Genes can be on either strand but RNA polymerase only works in the

Back 16

5' to 3' direction

Front 17

single stranded RNA can form

Back 17

structures

Front 18

RNA polymerse extends the growing RNA chain

Back 18

one nucleotide at a time; no primer is needed

Front 19

RNA polymerase make one mistake in

Back 19

10^4 nucleotides

Front 20

RNA does not need editing because

Back 20

it is not used for permanent storage of information

Front 21

mRNAs

Back 21

code for proteins

Front 22

rRNAs

Back 22

form the core of the ribosome and catalyze protein synthesis

Front 23

miRNAs

Back 23

regulate gene expression

Front 24

tRNAs

Back 24

serve as adaptors between mRNA and amino acids during protein synthesis

Front 25

other small RNAs

Back 25

used in RNA splicing, telomere maintenance and many other processes

Front 26

RNA polymerase in prokaryotes

Back 26

have a single type of RNA polymerase

Front 27

RNA polymerase in eukaryotes

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have three types of RNA polymerase
- RNA polymerase I, RNA polymerase II and RNA polymerase III

Front 28

Additional proteins in prokaryotes

Back 28

require sigma factor

Front 29

Additional proteins in eukaryotes

Back 29

require many additional proteins called general transcription factors

Front 30

DNA packing in eukaryotes

Back 30

eukaryotic transcription initiation must deal with the packing of DNA into nucleosomes and higher order forms of chromatin

Front 31

Signals in gene sequence act as

Back 31

start and stop in transcription

Front 32

the direction of transcripton is determined by the

Back 32

orientation of the promoter

Front 33

In eukaryotes mRNA is transcribed and processed in the

Back 33

nucleus

Front 34

Genes transcribed by RNA polymerase I

Back 34

most rRNA genes

Front 35

Genes transcribed by RNA polymerase II

Back 35

protein-coding genes, miRNA genes, plus genes for some small RNAs (eg those in splicesomes)

Front 36

Genes transcribed by RNA polymerase III

Back 36

tRNA genes
5S rRNA gene
Genes for many other small RNAs

Front 37

Eukaryotic RNA pol II requires

Back 37

accessory proteins

Front 38

TFIID binds

Back 38

TATA box and causes local distortion

Front 39

TATA binding protein (TBP) -

Back 39

binds TATA and distorts helix

Front 40

TFIIH phosphorylates the

Back 40

polymerase

Front 41

RFIIH pries apart double helix at

Back 41

start point and phosphorylates the polymerase; allows binding of RNA processing proteins

Front 42

mRNA processing - capping and polyadenylation

Back 42

7-methylguanosine at 5' end alings mRNA on the ribosome during translation
-poly-A tail at 3' end regulates stability and translation of mRNA
-Together the cap and poly A tail increase stability, aid in export, provide recognition of completion

Front 43

Splicing: additional RNA processing

Back 43

presence of noncoding sequences (introns)
coding sequences are called exons

Front 44

Introns were discovered using

Back 44

adenovirus mRNA;
examination of RNA-DNA hybrids in the electron microscope
hybrids are distinguishable from single stranded DNA

Front 45

Splicing takes place in large complexes called

Back 45

splicesomes

Front 46

Small nuclear ribonucleoprotein particles (snRNPs) assist in

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splicing

Front 47

Rearrangements that occur in the splicesome result in a complex that

Back 47

catalyzes the splicing reaction

Front 48

U1 and U2

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recognize sequences

Front 49

The regulation of RNA processing controls the

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expression of some proteins

Front 50

Fibroblast form adheres to the

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cell surface

Front 51

Hepatocyte form circulates in the

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serum

Front 52

Faulty gene splicing can lead to

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cancer and congenital diseases

Front 53

More than __ different splicing regulatory proteins have been identified

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10

Front 54

The nuclear pore complex controls transport

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to and from the nucleus

Front 55

mRNA export requires

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poly-A-binding protein and cap-binding protein

Front 56

Only fully processed mRNAs are transported to the ___. Processing occurs ______

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cytoplasm; vefore the transcript is completed

Front 57

Ribosomal and tRNA are very

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stable

Front 58

bacterial mRNAs are rapidly

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degraded; cells can respond quickly to the environment

Front 59

Eukaryotic mRNAs are degraded at

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Eukaryotic mRNAs are degraded at

Front 60

Short lived mRNAs contain multiple copies of

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AUUA in the 3' untranslated region

Front 61

How does information from mRNA translate into protein?

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Colinearity of genes and proteins - order of nucleotides specifies order of amino acids

Front 62

Messenger RNA carries information from DNA in a

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three letter code

Front 63

codon

Back 63

sequence of three nucleotides on the mRNA molecule that specifies an amino acid

Front 64

Most amino acids are represented by

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more than one codon - the genetic code is degenerate

Front 65

The start codon is

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AUG (methionine)

Front 66

There are three stop codons

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UAA, UGA and UAG

Front 67

The sequence of codons that runs from a specific start site to a terminating codon is called a

Back 67

reading frame

Front 68

The meaning of each codon is the same in most organisms - strong argument that

Back 68

life evolved only once

Front 69

How do we know that the reading frame is nonoverlapping?

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Analysis of mutationally altered proteins showed that only a single amino acid changes at one time in one region of the protein.

if it was an overlapping code than a single base change would alter as many as 3 amino acids

Front 70

How the code was deciphered

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Degraded endogenous mRNAs with RNase.

This RNA was mixed with ribosoems and aminoacyl-tRNAs in vitro

Result: protein made up of polyphenylalanine

Therefore, UUU codes for phenylalanine

Front 71

Conversion of information in RNA into protein is called

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translation

Front 72

mRNA can be in __ of ___ possible reading frames

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one of three

Front 73

Three kinds of RNA molecules are required for translation

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mRNA, tRNA and rRNA

Front 74

Messenger RNA

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encodes the genetic nformation copied from DNA

Front 75

transfer RNA

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deciphers the code by being an adapter between mRNA and A.A.

Front 76

ribosomal RNA

Back 76

catalyzing peptide bond formation

Front 77

all tRNAs have two functions

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to chemically link to a particular amino acid

recognize a codon in mRNA

Front 78

Amino acids are attached to the __ end of the appropriate tRNA molecule

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3'

Front 79

anticodon

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sequence of three nucleotides that is complementary to the codon

Front 80

Specific enzymes - aminoacyl-tRNA synthetases couple each amino acid to its

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appropriate tRNA molecule

Front 81

ribosomes are

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protein synthesizing machines

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Large subunit

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catalyzes peptide bond formation

this is an RNA catalyzed reaction (peptidyl transferase)

Proteins are thought to facilitate proper folding of the rRNA

Front 83

small subunit

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binds mRNA and tRNA

Front 84

____ are repsonsible for the ribosome's structure. ____ on surface stabilize the RNA core

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rRNAs; proteins

Front 85

Ribosomes provide three tRNA binding sites for protein elongation

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A site
P site
E site

Front 86

A site

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aminoacyl tRNA

Front 87

P Site

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peptidyl tRNA

Front 88

E Site

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(exit) transient site for deacylated tRNA (ejected)

Front 89

In eukaryotes, the small ribosomal subunit recognizes the

Back 89

5' cap of mRNA

Front 90

The ribosome then slids alog the mRNA to

Back 90

locate the AUG

Front 91

Initiation factors help the

Back 91

small subunit find the initiation site

Front 92

The initiator tRNA is distinct from the

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tRNA that normally carries methionine

Front 93

In bacteria, the small ribosomal subunit identifies

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initiation sites through interaction of sequences on the rRNA and mRNA- shine delgarno sequence

Front 94

procaryotic mRNA can encode

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several different proteins (polycistronic)

Front 95

The protein chain is released from the ribosome when

Back 95

one of the 3 stop codons is reached

Front 96

termination release factors bind to

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any stop codon that reaches the A-site

Front 97

Polyribosomes (polysome)

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several ribosomes spaces as close as 80 nucleotides apart along a single mRNA molecule

Front 98

Many antibiotics function by

Back 98

interfering with the function of prokaryotic ribosomes preferentially. These drugs selectively kill off the bacteria with no toxicity to humans.

Front 99

chaperones

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proteins that facilitate the folding of other proteins

Front 100

chaperones bind to the growing

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polypeptide chain, stabilizing it in the unfolded confomration until synthesis is complete

Front 101

proteins last

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months to sconds

Front 102

proteolysis

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enzymatic breakdown of proteins

Front 103

ubiquitin proteasome pathway

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Ubiquitin markes proteins for rapid proteolysis by a large multisubunit protease complex called a proteasome - cap protein selectively binds proteins

Front 104

RNA can

Back 104

store information and catalyze chemical reactions

Front 105

RNA in cells differs from DNA in that ___________________.
(a) it contains the base uracil, which pairs with cytosine
(b) it is single-stranded and cannot form base pairs
(c) it is single-stranded and can fold up into a variety of structures
(d) the sugar ribose contains fewer oxygen atoms than does deoxyribose

Back 105

Choice (c) is correct. Choice (a) is untrue because although RNA contains uracil, uracil pairs with adenine, not cytosine. Choice (b) is false because RNA can form base pairs with a complementary RNA or DNA sequence. Choice (d) is false because ribose contains one more oxygen atom than deoxyribose.

Front 106

Transcription is similar to DNA replication in that ___________________.
(a) an RNA transcript is synthesized discontinuously and the pieces are then joined together
(b) it uses the same enzyme as that used to synthesize RNA primers during DNA replication
(c) the newly synthesized RNA remains paired to the template DNA
(d) nucleotide polymerization occurs only in the 5′-to-3′ direction

Back 106

Choice (d) is correct. Choice (a) is incorrect because an RNA transcript is made by a single polymerase molecule that proceeds from the start site to the termination site without falling off. The enzyme used to make primers during DNA synthesis is indeed an RNA polymerase, but it is a special enzyme, primase, and not the enzyme that is used for transcription, which is why choice (b) is incorrect. Choice (c) is false

Front 107

For a cell’s genetic material to be used, the information is first copied from the DNA into the nucleotide sequence of RNA in a process called __________________. Various kinds of RNA are produced, each with different functions. __________________ molecules code for proteins, __________________ molecules act as adaptors for protein synthesis, __________________ molecules are integral components of the ribosome, and __________________ molecules are important in the splicing of RNA transcripts

Back 107

transcription; mRNA; tRNA; rRNA; snRNA

Front 108

Which of the following statements is false?
(a) A new RNA molecule can begin to be synthesized from a gene before the previous RNA molecule’s synthesis is completed.
(b) If two genes are to be expressed in a cell, these two genes can be transcribed with different efficiencies.
(c) RNA polymerase is responsible for both unwinding the DNA helix and catalyzing the formation of the phosphodiester bonds between nucleotides.
(d) Unlike DNA, RNA uses a uracil base and a deoxyribose sugar.

Back 108

Choice (d) is false. RNA nucleotides contain the sugar ribose.

Front 109

Which one of the following is the main reason that a typical eucaryotic gene is able to respond to a far greater variety of regulatory signals than a typical procaryotic gene or operon?
(a) Eucaryotes have three types of RNA polymerase.
(b) Eucaryotic RNA polymerases require general transcription factors.
(c) The transcription of a eucaryotic gene can be influenced by proteins that bind far from the promoter.
(d) Procaryotic genes are packaged into nucleosomes.

Back 109

c

Front 110

List three ways in which the process of eucaryotic transcription differs from the process of bacterial transcription.

Back 110

1. Bacterial cells contain a single RNA polymerase, whereas eucaryotic cells have three.
2. Bacterial RNA polymerase can initiate transcription without the help of additional proteins, whereas eucaryotic RNA polymerases need general transcription factors.
3. In eucaryotic cells, transcription regulators can influence transcriptional initiation thousands of nucleotides away from the promoter, whereas bacterial regulatory sequences are very close to the promoter.
4. Eucaryotic transcription is affected by chromatin structure and nucleosomes, whereas bacteria lack nucleosomes.

Front 111

In eucaryotic cells, general transcription factors are required for the activity of all promoters transcribed by RNA polymerase II. The assembly of the general transcription factors begins with the binding of the factor __________________ to DNA, causing a marked local distortion in the DNA. This factor binds at the DNA sequence called the __________________ box, which is typically located 25 nucleotides upstream from the transcription start site. Once RNA polymerase II has been brought to the promoter DNA, it must be released to begin making transcripts. This release process is facilitated by the addition of phosphate groups to the tail of RNA polymerase by the factor __________________. It must be remembered that the general transcription factors and RNA polymerase are not sufficient to initiate transcription in the cell and are affected by proteins bound thousands of nucleotides away from the promoter. Proteins that link the distantly bound transcription regulators to RNA polymerase and the general transc

Back 111

TFIID; TATA; TFIIH; Mediator; deacetylase

Front 112

You have a piece of DNA that includes the following sequence:

5′-ATAGGCATTCGATCCGGATAGCAT-3′
3′-TATCCGTAAGCTAGGCCTATCGTA-5′

Which of the following RNA molecules could be transcribed from this piece of DNA?

(a) 5′-UAUCCGUAAGCUAGGCCUAUGCUA-3′
(b) 5′-AUAGGCAUUCGAUCCGGAUAGCAU-3′
(c) 5′-UACGAUAGGCCUAGCUUACGGAUA-3′
(d) none of the above

Back 112

(b). The molecules listed in choices (a) and (c) have incorrect polarity.

Front 113

You have a segment of DNA that contains the following sequence:

5′-GGACTAGACAATAGGGACCTAGAGATTCCGAAA-3′
3′-CCTGATCTGTTATCCCTGGATCTCTAAGGCTTT-5′

If you know that the RNA transcribed from this segment contains the following sequence:

5′-GGACUAGACAAUAGGGACCUAGAGAUUCCGAAA–3′

Which of the following choices best describes how transcription occurs?
(a) The top strand is the template strand; RNA polymerase moves along this strand from 5′ to 3′.
(b) The top strand is the template strand; RNA polymerase moves along this strand from 3′ to 5′.
(c) The bottom strand is the template strand; RNA polymerase moves along this strand from 5′ to 3′.
(d) The bottom strand is the template strand; RNA polymerase moves along this strand from 3′ to 5′.

Back 113

(d). The bottom strand can hybridize with the RNA molecule and thus is the template strand. The polymerase moves along the DNA in a 3′ to 5′ direction, because the RNA nucleotides are joined in a 5′ to 3′ polarity.

Front 114

Which of the following molecules of RNA would you predict to be the most likely to fold into a specific structure as a result of intramolecular base pairing?

(a) 5′-CCCUAAAAAAAAAAAAAAAAUUUUUUUUUUUUUUUUAGGG-3′
(b) 5′-UGUGUGUGUGUGUGUGUGUGUGUGUGUGUGUGUGUGUGUG-3′
(c) 5′-AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA-3′
(d) 5′-GGAAAAGGAGAUGGGCAAGGGGAAAAGGAGAUGGGCAAGG-3′

Back 114

(a). Choices (b) and (c) do not have any opportunity for intramolecular base pairing and thus a specific structure is unlikely. Although there is some opportunity for intramolecular base paring in choice (d), choice (a) has much more intrastrand complementarity and is a better choice.

Front 115

Imagine that an RNA polymerase is transcribing a segment of DNA that contains the following sequence:

5′-AGTCTAGGCACTGA-3′
3′-TCAGATCCGTGACT 5′

If the polymerase is transcibing from this segment of DNA from left to right, which strand is the template?

What will be the sequence of that RNA (be sure to label the 5′ and 3′ ends of your RNA molecule)?

Back 115

bottom

5′-AGUCUAGGCACUGA-3′

Front 116

The sigma subunit of bacterial RNA polymerase ___________________.
(a) contains the catalytic activity of the polymerase
(b) remains part of the polymerase throughout transcription
(c) recognizes promoter sites in the DNA
(d) recognizes transcription termination sites in the DNA

Back 116

c

Front 117

Which of the following might decrease the transcription of only one specific gene in a bacterial cell?
(a) a decrease in the amount of sigma factor
(b) a decrease in the amount of RNA polymerase
(c) a mutation that introduced a stop codon into the DNA that precedes the gene’s coding sequence
(d) a mutation that introduced extensive sequence changes into the DNA that precedes the gene’s transcription start site

Back 117

(d). Such changes would probably destroy the function of the promoter, making RNA polymerase unable to bind to it. Decreasing the amount of sigma factor or RNA polymerase (choices (a) or (b)) would affect the transcription of most of the genes in the cell, not just one specific gene. Introducing a stop codon before the coding sequence (choice (c)) would have no effect on transcription of the gene, because the transcription machinery does not recognize translational stops.

Front 118

There are several reasons why the primase used to make the RNA primer for DNA replication is not suitable for gene transcription. Which of the statements below is not one of those reasons?
(a) Primase initiates RNA synthesis on a single-stranded DNA template.
(b) Primase can initiate RNA synthesis without the need for a base-paired primer.
(c) Primase synthesizes only RNAs of about 5–20 nucleotides in length.
(d) The RNA synthesized by primase remains base-paired to the DNA template.

Back 118

Choice (b) is true for both primase and RNA polymerase, so it does not describe why primase cannot be used for gene transcription.

Front 119

You have a bacterial strain with a mutation that removes the transcription termination signal from the Abd operon. Which of the following statements describes the most likely effect of this mutation on Abd transcription?
(a) The Abd RNA will not be produced in the mutant strain.
(b) The Abd RNA from the mutant strain will be longer than normal.
(c) Sigma factor will not dissociate from RNA polymerase when the Abd operon is being transcribed in the mutant strain.
(d) RNA polymerase will move in a backwards fashion at the Abd operon in the mutant strain.

Back 119

(b). Without the termination signal, the polymerase will not halt and release from the DNA template at the normal location when transcribing the Abd operon. Most probably, the polymerase will continue to transcribe RNA until it reaches a sequence in the DNA that can serve as a termination sequence, either from the next downstream operon or in the intervening sequence between the Abd operon and the next operon. Dissociation of sigma factor occurs once an approximately 10-nucleotide length of RNA has been synthesized by RNA polymerase and should not be affected by the lack of a termination signal (choice (c)).

Front 120

Transcription in bacteria differs from transcription in a eucaryotic cell because __________________________.
(a) RNA polymerase (along with its sigma subunit) can initiate transcription on its own
(b) RNA polymerase (along with its sigma subunit) requires the general transcription factors to assemble at the promoter before polymerase can begin transcription
(c) The sigma subunit must associate with the appropriate type of RNA polymerase to produce mRNAs
(d) RNA polymerase must be phosphorylated at its C-terminal tail for transcription to proceed

Back 120

a). Eucaryotic cells, but not bacteria, require general transcription factors (choice (b)). There is only a single type of RNA polymerase in bacterial cells (choice (c)). The general transcription factor TFIIH phosphorylates the C-terminal tail of RNA polymerase in eucaryotic cells but not in bacteria (choice (d)).

Front 121

Which of the following does not occur before a eucaryotic mRNA is exported from the nucleus?
(a) The ribosome binds to the mRNA.
(b) The mRNA is polyadenylated at its 3′ end.
(c) 7-methyl-G is added in a 5′ to 5′ linkage to the mRNA.
(d) RNA polymerase dissociates.

Back 121

(a). Ribosomes are in the cytosol and will bind to the mRNA once it has been exported from the nucleus

Front 122

Total nucleic acids are extracted from a culture of yeast cells and are then mixed with resin beads to which the polynucleotide 5′-TTTTTTTTTTTTTTTTTTTTTTTTT-3′ has been covalently attached. After a short incubation, the beads are then extracted from the mixture. When you analyze the cellular nucleic acids that have stuck to the beads, which of the following is most abundant?
(a) DNA
(b) tRNA
(c) rRNA
(d) mRNA

Back 122

(d). mRNA is the only type of RNA that is polyadenylated, and its poly A tail would be able to base-pair with the strands of poly T on the beads and thus stick to them. DNA would not be found in the sample, because the poly A tail is not encoded in the DNA and long runs of T are rare in DNA.

Front 123

Name three covalent modifications that can be made to an RNA molecule in eucaryotic cells before the RNA molecule becomes a mature mRNA.

Back 123

1. A poly A tail is added.
2. A 5′ cap is added.
3. Introns can be spliced out.

Front 124

Which of the following statements about RNA splicing is false?
(a) Conventional introns are not found in bacterial genes.
(b) For a gene to function properly, every exon must be removed from the primary transcript in the same fashion on every mRNA molecule produced from the same gene.
(c) Small RNA molecules in the nucleus perform the splicing reactions necessary for the removal of introns.
(d) Splicing occurs after the 5′ cap has been added to the end of the primary transcript

Back 124

(b). The primary transcript of a gene can sometimes be spliced differently so that different exons can be stitched together to produce distinct proteins in a process called alternative splicing.

Front 125

The length of a particular gene in human DNA, measured from the start site for transcription to the end of the protein-coding region, is 10,000 nucleotides, whereas the length of the mRNA produced from this gene is 4000 nucleotides. What is the most likely reason for this difference?

Back 125

The gene contains one or more introns

Front 126

Why is the old dogma “one gene—one protein” not always true for eucaryotic genes?

Back 126

The transcripts from some genes can be spliced in more than one way to give mRNAs containing different sequences, thus encoding different proteins. A single eucaryotic gene may therefore encode more than one protein.

Front 127

Is this statement true or false? Explain your answer.

“Since introns do not contain protein coding information, they do not have to be removed precisely (meaning, a nucleotide here and there should not matter) from the primary transcript during RNA splicing.”

Back 127

False. Although it is true that the sequences within the introns are mostly dispensable, the introns must still be removed precisely because an error of one or two nucleotides would shift the reading frame of the resulting mRNA molecule and change the protein it encodes.

Front 128

You have discovered a gene (Figure Q7-27A) that is alternatively spliced to produce several forms of mRNA in various cell types, three of which are shown in Figure Q7-27B. The lines connecting the exons that are included in the mRNA indicate the splicing. From your experiments, you know that protein translation begins in exon 1. For all forms of the mRNA, the encoded protein sequence is the same in the regions of the mRNA that correspond to exons 1 and 10. Exons 2 and 3 are alternative exons used in different mRNA, as are exons 7 and 8. Which of the following statements about exons 2 and 3 is the most accurate? Explain your answer.

(a) Exons 2 and 3 must have the same number of nucleotides.
(b) Exons 2 and 3 must contain an integral number of codons (that is, the number of nucleotides divided by 3 must be an integer).
(c) Exons 2 and 3 must contain a number of nucleotides that when divided by 3, leaves the same remainder (that is, 0, 1, or 2).
(d) Exons 2 and 3 must have different numbers of nucleotide

Back 128

Choice (c) is the only answer that must be true for exons 2 and 3. Although choices (a), (b), and (d) could be true, they do not have to be. Because the protein sequence is the same in segments of the mRNA corresponding to exons 1 and 10, the choice of either exon 2 or exon 3 would not alter the reading frame. To maintain the normal reading frame, whatever it is, the alternative exons must have a number of nucleotides that when divided by 3 (the number of nucleotides in a codon) give the same remainder.

Front 129

Which of the following statements about the genetic code is correct?
(a) All codons specify more than one amino acid.
(b) The genetic code is redundant.
(c) All amino acids are specified by more than one codon.
(d) All codons specify an amino acid.

Back 129

(b). Most amino acids can be specified by more than one codon. Each codon specifies only one amino acid (choice (a)). Tryptophan and methionine are encoded by only one codon (choice (c)). Some codons specify translational stop signals (choice (d)).

Front 130

The piece of RNA below includes the region that codes the binding site for the initiator tRNA needed in translation.

5′-GUUUCCCGUAUACAUGCGUGCCGGGGGC-3′

Which amino acid will be on the tRNA that is the first to bind to the A-site of the ribosome?
(a) methionine
(b) arginine
(c) cystine
(d) valine

Back 130

(b). The initiator methionine is underlined on the RNA molecule below.

5′-GUUUCCCGUAUACAUGCGUGCCGGGGGC-3′

The first tRNA to bind at the A-site is the second codon of the protein, because the initiator tRNA is already bound to the P-site when translation begins. The codon that follows the binding site for the initiator tRNA is CGU, which codes for arginine.

Front 131

The following DNA sequence includes the beginning of a sequence coding for a protein. What would be the result of a mutation that changed the C marked by an asterisk to an A?

5′-AGGCTATGAATGGACACTGCGAGCCC….

Back 131

The change creates a stop codon (TGA, or UGA in the mRNA) very near the beginning of the protein-coding sequence and in the correct reading frame (the beginning of the coding sequence is indicated by the ATG). Thus, translation would terminate after only four amino acids had been joined together, and the complete protein would not be made.

Front 132

Which amino acid would you expect a tRNA with the anticodon 5′-CUU-3′ to carry?
(a) lysine
(b) glutamic acid
(d) leucine
(d) phenylalanine

Back 132

(a). As is conventional for nucleotide sequences, the anticodon is given reading from 5′ to 3′. The complementary base-pairing occurs between antiparallel nucleic acid sequences, and the codon recognized by this anticodon will therefore be 5′-AAG-3′.

Front 133

Which of the following pairs of codons might you expect to be read by the same tRNA as a result of wobble?
(a) CUU and UUU
(b) GAU and GAA
(c) CAC and CAU
(d) AAU and AGU

Back 133

Choice (c) is the correct answer. These two codons differ only in the third position and also encode the same amino acid, which is the definition of wobble. Although the codons GAU and GAA (choice (b)) also differ only in the third position, they are unlikely in normal circumstances to be read by the same tRNA, because they encode different amino acids.

Front 134

Below is a segment of RNA from the middle of an mRNA.

5′-UAGUCUAGGCACUGA-3′

If you were told that this segment of RNA was part of the coding region of an mRNA for a large protein, give the amino acid sequence for the protein that is encoded by this segment of mRNA. Write your answer using the one-letter amino acid code.

Back 134

SLGT is the correct answer. (Reading frame two is the only reading frame that does not contain a stop codon.)

Front 135

Portions of DNA sequences are transcribed into

Back 135

RNA

Front 136

Transciption produces

Back 136

RNA complementary to one strand of DNA

Front 137

Several types of RNA are produced in

Back 137

cells

Front 138

Signalsin DNA tell RNA polymerase

Back 138

where to start and finish

Front 139

Eucaryotic RNAs are transcribed and processed

Back 139

simultaneously in the nucleus

Front 140

Eucaryotic genes are interrupted by

Back 140

noncoding sequences

Front 141

Introns are removed by

Back 141

RNA splicing

Front 142

Mature eucaryotic mRNAs are selectively

Back 142

exported from the nucleus

Front 143

mRNA molecules are eventually

Back 143

degraded by the cell

Front 144

The earliest cells may have had

Back 144

introns in their genes

Front 145

An mRNA sequence is decoded in

Back 145

sets of three nucleotides

Front 146

tRNA molecules match

Back 146

amino acids to codons in mRNA

Front 147

Specific enzymes couple tRNAs to the

Back 147

correct amino acid

Front 148

the RNA message is decoded on

Back 148

ribosomes

Front 149

Codons in mRNA signal where to

Back 149

start and stop protein synthesis

Front 150

proteins are made on

Back 150

polyribosomes

Front 151

inhibitorsf procaryotic protein synthesis are used as

Back 151

antibiotics

Front 152

carefully controlled protein breakdown helps regulate the amount of each

Back 152

proten i a cell

Front 153

Life requires

Back 153

autocatalysis

Front 154

RNA can both

Back 154

store information and catalyze chemical reactions

Front 155

RA is thought to __ DNA in evolution

Back 155

predate

Front 156

Genetic information directs the synthesis of protein:

Back 156

the flow of genetic information from DNA to RNA (transcription) and from RNA to protein (translation) occurs in all living cells

Front 157

Genes can be expressed with __ efficiencies

Back 157

different

Front 158

RNA contains the sugar

Back 158

ribose

Front 159

RIbose differs from deoxyribose by the

Back 159

presence of an additional -OH group

Front 160

RNA contains the base ___ which differs from ___, the equivalent base in DNA by the _____

Back 160

uracil; thymine; absence of a -CH3 group

Front 161

The chemical linkage between nucleotides in RNA is the __ as that in DNA

Back 161

same

Front 162

uracil forms a base pair with

Back 162

adenine

Front 163

The genetic instructions carried by DNA specify the

Back 163

the amino acid sequence of proteins

Front 164

DNA does not direct protein synthesis itself, but acts

Back 164

rather like a manager, delegating the various taksks required.

Front 165

When a protein is needed by the cell, the nucleotide sequence of the appropriate portion of the immensly long DNA molecule in a chromosome is first copied into another type of nucleic acid ______

Back 165

RNA

Front 166

RNA copies of short segments of DNA are used as

Back 166

templates to direct synthesis of the protein

Front 167

Central Dogma of molecular biology

Back 167

All cells express their tenetic information with the flow of DNA to RNA to protein

Front 168

Transcription

Back 168

The mechanisms by which cells copy DNA into RNA

Front 169

Translation

Back 169

using the information in RNA to make a protein

Front 170

RNA splicing

Back 170

All cells express their tenetic information with the flow of DNA to RNA to protein

Front 171

RNA splicing alterations chane the ____ of the RNA molecules and are therefore crucial for understanding how cell ___ the genome.

Back 171

meaning; decode

Front 172

The flow of genetic information from DNA to RNA (_____) and from RNA to protein (____) occurs in all living cells

Back 172

transcription; translation

Front 173

Transcription and translation are the means by which cells

Back 173

readout or express their genetic instructions

Front 174

____ identical RNA copies can be made from the same gene, and each RNA molecule can direct the synthesis of ___ identical protein molecuels

Back 174

many; many

Front 175

Each cell contains only one or two copies of a particular gene. How are enough cells synthesized to create the required amount of protein?

Back 175

Successive amplification enables cells to synthesize the required amount of a protein much more rapidly than if the DNA itself were acting as the direct template for protein synthesis. Many identical RNA copies can be made from the same gene and each RNA molecule can direct the synthesis of many identical protein molecules.

Front 176

Each gene can be transcribed and translated with a different efficiency and this provides the cell with a way to make

Back 176

vast quantities of some proteins and tiny quantities of others

Front 177

The first step a cell takes in reading out part of its genetic instructions is to ___________________ . This process is called ____ because ____________

Back 177

to copy the required portion of the nucleotide sequence of DNA - the gene - into a nucleotide sequence of RNA; transcription; the information, though copied into another chemical form, is still written in the language of nucleotides

Front 178

RNA is a liear polymr made of ___ different typesof nucleotide subunits linked together by ___ bonds

Back 178

four; phosphodiester

Front 179

RNA differs from DNA cemically in two respcts:

Back 179

1. the nucleotides in RNA are ribonucleotides; that is, they caontain the sugar ribose
2. it contains uracil instead of thymine

Front 180

RNA is structurally different than DNA in that it is ____. The functional consequences of this are:

Back 180

single stranded;

The RNA chain an fold into a variety of shapes which allows RNA to carry out functions in cells in addition to conveying info between DNA and protein

Front 181

Ribose is used in

Back 181

RNA

Front 182

Deoxyribose is used in

Back 182

DNA

Front 183

RNA contains the sugar ribose which differs from deoxyribose by the presence of

Back 183

an additional -OH group

Front 184

RNA contains the base uracil, which differs from thymine by

Back 184

the absence of a -CH3 group

Front 185

All of the RNA in a cell is made by ___, a process that has certain similarities to DNA replication

Back 185

Transcription

Front 186

Uracil forms a base pair with

Back 186

adenine

Front 187

Despite the absence of a ___ group, uracil has the same base pairing properties as thymine. U-A base pairs __ ___ T-A base pairs.

Back 187

methyl; closely resemble.

Front 188

Transcription begins with

Back 188

opening and unwinding of a small portion of the DNA double helix to expose te bases on each DNA strand.

Front 189

During transcription, one of the two strands of the DNA double helix acts as a: _____. ___ are added; __ by ___ to the growing RNA chain, and as in DNA replication, the nucleotide sequence of the RA chain is determined by __________

Back 189

template for synthesis of RNA; Ribonucleotides; one-by-one; complementary base pairing with the DNA template.

Front 190

The incoming ribonucleotide is ___ linked to the growing RNA chain in an _____ ____ reaction.

Back 190

covalently; enzymatically catalyzed

Front 191

The RNA chain produced by transcrption is elongated ___ ___ __ __ __ and has a nucleotide sequence __ __ to the stand of DNA used as the templaet

Back 191

one nucleotide at a time; exactly complmentary

Front 192

RNA is single stranded, but it often contains short streches of nucleotides that can _______________________. Thes interactions, along sith "nonconventioanl" base pair interactions allow an RNA molecule to:

Back 192

base-pair with complementay sequences found elsewhere on the same molecule.

fold into a three-dimensional structure that is determined by its sequence of nucleotides

Front 193

Unlike a newly formed DNA strand, the RNA strand does not remain hydrogen-bonded o the DNA template strand. Instead,

Back 193

just behind the region where he ribunucleotides are being added, the DNA helix re-forms and displaces the RNA chain.

Front 194

Why are RNA molecules single stranded?

Back 194

The DNA helix re-forms and displaces the RNA chain

Only one strand of the DNA molecule is transcribed

Front 195

DNA molecuels in a human chromosome can be up to 250 million nuclotide pairs long whereas mot RNAs are no mor than

Back 195

a few thousand long and many are much shorter than that

Front 196

The enzymes that carry out transcription

Back 196

RNA polymerases

Front 197

RNA polymerases catalyze the formation of the

Back 197

phosphodiester bonds that link the nucleotides together and form the sugar phosphate backbone of the RNA chain.

Front 198

The RNA polymerase moves ___ along the DNA, ____ the DNA helix just ahead to expose a new region of the template strand for complementary base pairing.

Back 198

stepwise; unwinding;

Front 199

The growing RNA chain is extended by one ucleotide at a time in the ___ direction, using ribonucleoside triphosphates (_______), whose high energy bonds provide the energy that drives the reaction forward.

Back 199

5'-to-3'

ATP, CTP, UTP, and GTP

Front 200

The almost immediate release of the RNA strand from the DNA as it is synthesized means that

Back 200

many RNA copies can b made from the same gene in a relatively short time;

the synthesis of the next RNA usually is started before the first is completed.

Front 201

The top strand is sometimes called the __ ___ because its sequence is equivalent to the RNA product

Back 201

coding strand

Front 202

Differences between RNA polymerase and DNA polmerase

Back 202

RNA polymerase catalyzes the linkage of ribonucleotides

RNA polymerases can start an RNA chain without a primer

Front 203

The RNA molecules that are copied from genes (and that ultimately direct the synthesis of proteins) are called

Back 203

messenger RNA

Front 204

Nonmessenger RNAs, like proteins,serve as

Back 204

structural and enzymatic components of cells and play key parts in translating the genetic message into protein

Front 205

Ribosomal RNA forms ________ on which mRNA is __________ and transfer RNA foms the _________________.

Back 205

the core of he ribosomes; translated into protein;
adaptors that select amino acids and hold them in place on a ribosome for their incorporation into protein

Front 206

Code for proteins

Back 206

mRNAs

Front 207

Form part of the structure of the ribosome and participate in protein synthesis

Back 207

rRNAs

Front 208

Used in protein synthesis as adaptors between mRNA and amino acids

Back 208

tRNAs

Front 209

Used in pre-mRNA splicing, transport of proteins to the ER and other cellular processes

Back 209

small RNAs

Front 210

In eucaryotes, each mRNA typically carries information transcribed from ____, coding for a ______

Back 210

one gene; single protein

Front 211

In bacteria, a set of adjacent genes is often transcribed as a _____ that therefore carries the information for ____

Back 211

single mRNA; several different proteins

Front 212

The initiation of transcription is the

Back 212

main point at which the cell regualtes which proteins are to beproduced at wat rate

Front 213

RNA polymerase molecules tend to ____ to the DNA when they randomly collide with it; the polymerase molecule then ______

Back 213

stick weekly; slides rapidly along the DNA

Front 214

RNA polymerase latches tightly onto te DNA once it encounters a region called a _____

Back 214

promoter

Front 215

Promoter

Back 215

contains a sequence of nucleotides indicating the starting point for RNA synthesis

Front 216

The polymerase protein can recognize the DNA promoter sequence by

Back 216

making speciic cotacts with the portions of the bases that are exposed on the outside of the helix

Front 217

After the RNA polymerase makes contact with the promoter DNA and binds to it tighly, the enzyme

Back 217

opens up the double helix immediately in front of it to expose the nucleotides on a short stretch of DNA on each strand. One of the two exposed strands then acts as a template

Front 218

Chain elongation continues until the enzyme encounters a second signal in the DNA, the

Back 218

terminator (or stop site), where the polymerase halts and releases both the DNA template and the newly made RNA chain.

Front 219

A subunit of bacterial polymerase, called sigma factor, is primarily responsible for

Back 219

recognizing the promoter sequence on DNA.

Front 220

Bacterial RNA polymerase contains a subunit called the _ ___ that recognizes the ___ on the DNA. Once transcriptionhas begun, the sigma factor i released and the polymerase continues synthesiszing the RNA without it. Chain elongation continues until the polymerase encounters a ___ in the DNA.

There the enzyme halts and releases both the ___ and the newly made ___.

Polymerase then reassociates with a _____ and searchers for another __ to begin the process again.

Back 220

sigma factor; promoter; terminal signal

DNA template; transcript

free sigma factor; promoter

Front 221

Because DNA is souble stranded, two different RNA molecules could in principle be transcribed from any gene. However, the promoter is:

Back 221

asymmetrical and binds the polymerase in only one orientation.

Front 222

The direction of the transcription is determined by the ___ of the ___at the ____ of each gene.

Back 222

orientation; promoter; begining

Front 223

The RNA polymerase's requirement for bindig tightly to DNA before it can start transcription means that a portion of DNA can be transcribed only if it is preceded by a ___ ___. THis ensure that

Back 223

promoter sequence

only those parts of a DNA molecuel that contain a gene will be transcribed into RNA.

Front 224

Before they can be translated, mRNA molecuels made in the nucleus move out into the cytoplasm via

Back 224

pores in the nuclear envelope

Front 225

Bacterial DNA lies directly exposed to the cytoplasm which contains the ___ on which protein sytnesis takes place. As mRNA molecules in bacteria are transcribed, ribosomes immediately attach to the ____ of the RNA transcript and protein synthesis starts.

Back 225

ribosomes; free 5' end;

Front 226

In eucaryotic cells DNA is enclosed: ____.

Transcription takes place in the ___, but protein synthesis takes place on ___ in the ____.

Back 226

within the nucleus; nucleus; ribosomes; cytoplasm

Front 227

Before a eucaryotic mRNA can be translated, it must be

Back 227

transported out of the nucleus

Front 228

Before a eucaryotic RNA exists the nucleus, it must go through several different _____ steps

Back 228

RNA processing.

Front 229

Depending on which type of RNA is being produced, the transcripts are processed in ___ ___ before leaving the nucleus

Back 229

various ways

Front 230

Two processing steps that occur only on transcripts destine to become mRNA molecules are ___ and ____

Back 230

RNA capping; polyadenylation

Front 231

Unlike bacterial mRNAs, eucaryotic mRNA molecuels are modified by

Back 231

capping and polyadenylation.

Front 232

The 5' and 3' ends of a bacterial mRNA are the ___ ends of te chain synthesized by the RNA polymerase, which initiates and terminates transcription at those points.

The corresponding ends of a eucaryotic mRNA are modified by the addition of a ___ and by ___ of the primary transcript and the addition of a ____ , respectively

Back 232

unmodified;

5' cap; cleavage; poly-A tail

Front 233

Bacterial mRNAs can contain the instructions for several different proteins, whereas eucaryotic mRNAs

Back 233

nearly always contain the information for only a single protein

Front 234

RNA capping involves a modification of the ___ end of the mRNA transcript, the end that is synthesized __ during transcription.

The RNA is capped by the addition of an atypical nucleotide - a ___ nucleotide with a ___ group attached.

This capping occurs after the RNA polymerase has produced about __ nucleotides of RNA, long before it has completed transcriibing the whole gene

Back 234

5'; first; guanine; methyl; 25

Front 235

Polyadenylation provides most newly transcribed mRNAs with a special structure at their __ or __ ends.

The 3' ends of eucaryotic RNAs are first trimmed by an enzyme that ___ the ___ chainat a particualr sequence of nucleotides and are then finished off by a second enzyme that adds a series of repeated ___ nucleotides (a ____) onto the cut end. The ____ is generally a few hundred nucleotides lon.

Back 235

3'; tail; cuts; RNA chain; adenine; poly-A tail; poly-A tail

Front 236

Capping andpolyadenylation are thought to

Back 236

increase stability of the eucaryotic mRNA molecule, to aid is export from the nucleus to the cytoplasm and to generally identify the RNA molecuel as an mRNA.

Front 237

A bacterial gene consists of a single stretch of ___ ___ sequence that encodes the amino acid sequence of a protein.

In contrast, the coding sequences of most eucaryotic genes (___) are interrupted by noncoding sequences (___).

Back 237

uninterrupted nucleotide

exons; introns

Front 238

intervening sequences

Back 238

introns

Front 239

coding or expressed sequences

Back 239

exons

Front 240

exons are usually ___ than the introns and the coding portion of a eucaryotic gene is often a ___ fraction of the total length

Back 240

shorter; small

Front 241

To produce an mRNA in a eucaryotic cell, the entire length of the gene is transcried into RNA. After capping, as the RNA polymerase contiues to transcribe the gene, the process of RNA splicing begins, in which: __________________

Each transcript ultaimately receives a ____.

Back 241

the intron sequences are removed from the newly synthesized RNA and the exons are stitched together.

poly-A tail

Front 242

Once a transcript has been spliced and its 5' and 3' end have been modified, the RNA is a

Back 242

funcational mRNA molcule that can now leave the nucleus and be translated into protein.

Front 243

Special sequences are recognized by small nuclear ribonucleoproteins (snRNPs), whih

Back 243

cleave the RNA at the intron-exon borders and covalently link the exons together.

Front 244

Each intron contains a few short nucleotide sequences that act as cues for its removal. These sequences are found:

Back 244

at or near each end of the intron and are the same or very similar in all introns

Front 245

The intron is cut out in the form of a ___ structure formed by the reaction of the __ with the __ splice junction of the intron

Back 245

lariat; A; 5'

Front 246

RNA splicing is perormed largely by ___ instead of proteins

Back 246

RNA molecules

Front 247

RNA molecules recgnize intron-exon boundaries and participate in the

Back 247

chemistry of splicing

Front 248

RNA molecules called __________ bind with additional proteins t form ____________. These ___ form the core of he ___, the large assembly of RNA and protein molecules that performs RNA splicing in the cell

Back 248

small nuclear RNAs snRNAs
small nuclear ribonucleoprotein particles (snRNPs);
snRNPs
Splicesome

Front 249

An RNA chain forms a ____ structure during splicing

Back 249

branched

Front 250

Spicing:
In the first step, a particular adenine nucleotide in the intron sequence attacks the _____ and cuts the _____ bacbone of the RNA at this point.

The cut 5' end of the intron becomes ____ linked to the ___ nucleotide to form a branched structure.

The free 3'-PH end of the exon sequence then reacts with the __ of the next __ sequence, joining the two exons together into a continuous coding sequence and releasing the __ in the form of a ___.

Back 250

5' splice site;
sugar phosphate
covalently;
adenine;
start; exon; intron; lariat

Front 251

Structure of the lariat branch:

Back 251

The cut 5' end of the intron is linked to the 2' OH group of the ribose of the branchpoint adenine nucleotide.

Front 252

RNA splicing is catalyzed by an assembly of ____ plus __ __ whic together form the ____

Back 252

snRNPs; other proteins; spliceosome

Front 253

The transport of mRNA from the nucleus to the cytoplasm, where it is translated into protein, is highly selective, as it is closly couple to correct RNA processing. This coupling is achieved by the ___________, which recognizes and transports only comleted mRNAs.

Back 253

nuclear pore complex

Front 254

A specialized set of RNA binding proteins mark a mature mRNA for ________

Back 254

export to the cytoplasm

Front 255

Nuclear transport receptor

Back 255

dedicated to mRNA export - associates with mature mRNAs and actively guides them through tne nuclear pore

Front 256

Once in the cytoplasm, the mRNA continues to shed previously bound proteins and acquire new ones. These substitutions affect the

Back 256

subsequent translation of the message

Front 257

The conversion of the information in RNA into protein represents a____ of the information

Back 257

translation

Front 258

The rules by which the nucleotide sequence ofa gene, through the medium of mRNA is translatedinto the amino acid sequence of a protein are known as the

Back 258

genetic code

Front 259

The sequence of nucleotides in the mRNA moelcule is read consecutively in grous of

Back 259

three

Front 260

Each group of three consecutive nucleotides in RNA is called a ___ and each specifies _____

Back 260

codon; one amino acid

Front 261

In principle, an RNA sequence can be translated in any one of three different, nonoverlapping ___ depending on where the decoding process begins

Back 261

reading frames

Front 262

In the process of translating a nucleotide sequence, the sequence of nucleotides in an mRNA is read from the __ to the __ end in sequential sets of three nucleotides. In principle the same RNA sequence can specify three completely different amino acid sequences depending on the reading frame. In reality, _____

Back 262

5 to the 3';

only one of these reading frames encodes the actual message

Front 263

The translation of mRNA into protein depends on ___ ___ that can recgnize and bind both to the codon and to the amino acid. These are known as:

Back 263

adaptor molecuels; tRNAs

Front 264

Two regions of unpaire nucleotides situated at either end of the L-shaped molecule are crucial to the functin of tRNA in protein synthesis. One forms the ____, a set of three consecutive nucleotides that pairs with the complmentary codon in an mRNA molecule. The other is a short single stranded region at the __ end of the molecule; this is the site whre the amino acid that matches the codon is attached to the tRNA

Back 264

anticodon; 3'

Front 265

Recognition and attachement of the correct amino acid depends on enzymes called _______, which covalently couple each amino acid to its appropriate set of tRNA molecules.

Back 265

aminoacyl-tRNA synthetases

Front 266

The genetic code is translated by means of two adaptors that act one after another

Back 266

First: the aminoacyl-tRNA synthetase which couples a particular amino acid to its corresponding tRNA; Charging

second: tRNA molecule itself whose anticodon forms base pairs with the appropriate codon on the mRNA

Front 267

A tRNA coupled with its amino acid is calld a

Back 267

charged tRNA

Front 268

An error in either step - charging or binding will cause the

Back 268

wrong amino acid to be incorporated into a protein chain

Front 269

The small subunit matches the ___ to the __ of the mRNA; while the large subunit catalyzes the formation of the ___ ___ that link the amino acids together.

Back 269

tRNAs; codons; peptide bonds

Front 270

Ribosomes are found in the ___

Back 270

cytoplasm

Front 271

Eah ribosome has a binding sie for mRNA and three binding sites for tRNA.

tRNA sites:

Back 271

A- P- E-

Front 272

An mRNA molecule is translated in a three step cycle

Back 272

Each amino acid added is selected by complementary base pairing between the anticodon on its attached tRNA molecule and the next codon on the mRNA chain.

The codon determines the speicif amino acid to be addd.

1. An aminoacyl-tRNA molecule binds to a vacant A site on the ribosome

2. A new peptide bond is formed

3. the mRNA moves a distance of three nucleotides through the small subunit, ejecting the spent tRNA molecule and resetting the ribosome.

Front 273

RNA molecules that possess catalytic activity

Back 273

ribozymes

Front 274

Codons in mRNA signal where to

Back 274

start and stop synthesis

Front 275

The___ ___ always carries the amino acid methionine so that newly made proteins all have methionine as the first amino acid at their N-terminal end.

Back 275

initiator tRNA

Front 276

In eucaryotes, the initiator tRNA which is coupled to methionine is first loaded into the small ribosomal subunit along with additional protins called

Back 276

translation initiation factors

Front 277

In the final phase of protein synthesis, the binding of release factor to an A site bearing a stop codon terminates

Back 277

translation.

Front 278

Proteins are translated by

Back 278

polyribosomes

Front 279

The flow of genetic information in all living cells is

Back 279

DNA -> RNA -> protein

Front 280

The conversion of the genetic instructions in DNA into RNAs and proteins is termed

Back 280

gene expression

Front 281

To express the genetic information carried in DNA, the nucleotide sequence of a gene is first ______

Back 281

transcribed into RNA.

Front 282

Transcription is catalyzed by the enzyme

Back 282

RNA polymerase

Front 283

Nucleotide sequences in the DNA molecule indicate to the RNA polymerase where to

Back 283

start and stop transcribing

Front 284

Cells make several different functional types of RNA including mRNA, which ______________; rRNA, which ___________; and tRNA, which ________

Back 284

carries the instructions for making prteins

a component of ribosomes

acts as an adaptor molecule in protein synthesis

Front 285

Eucaryotic mRNAs go through several additional RNA processing steps before they leave the nucleus, including ______ and ____. These reactions along with splicing are tightly coupled to transcription and take place as the RNA is being transcribed. The mture mRNA then moves to the ____

Back 285

RNA capping; polyadenylaton; cytoplasm

Front 286

Tranlation of the nucleotide sequence of mRNA into a protein takes place in the ____ on large ribonucleoprotein assemblies called_____.

These attache to the mRNA and move stepwise along the mRNA chain, translating the message into protein

Back 286

cytoplasm; ribosomes

Front 287

The correspondence between amino acids and codon is specified by the ___ ___. The possible combinatiosof 4 different nucleotides in RNA give ___ diffeent codons in the genetic code. Most amino acids are speicied by ____ codon

Back 287

genetic code; 64; more than one

Front 288

tRNA acts as an adaptor molecule in protein synthesis. Enzymes called ____ link amino acids to their appropriate tRNAs. Each tRNA contains a sequence of three nucleotides, the ___ which matches a codon in mRNA by compelementary base pairing between codon an anticodon

Back 288

aminoacyl-tRNA; anticodon;

Front 289

Protein synthesis begins when a ribosome assembles at an initiationcodon ___ in mRNA, a process that is regulated by proteins called ___________. The completed protein chain is released from the ribosome when a stop codon ______ is reached

Back 289

AUG; translation initiation factors; UAA, UAG, or UGA

Front 290

The stepwise linking of amino acids into a polypeptide chain is catalyzed by an __ molecule in the ____ ____ ___. Thus the ribosome is an example of a ___, an RNA molecule that can catalyze a chemical reaction

Back 290

rNA; large riboomal subunit; riboxyme

Front 291

The degradation of poteins in the cell is carefully controlled. Some proteins are degraded in the cytosol b large protein complexes called

Back 291

proteasomes