Bio Chapter 13

Front 1

• Transcription

Back 1

– the synthesis of RNA molecules complementary to the DNA

Front 2

• Translation

Back 2

The second major step, in which RNA becomes a coded template to direct polypeptide (protein) synthesis

Front 3

• Beadle and Tatum

Back 3

Can genes code for enzymes?

Front 4

thymine

Back 4

Uracil is substituted for

Front 5

• Transcription

Back 5

RNA synthesis takes the information in one kind of nucleic acid (DNA) and copies it as another nucleic acid (RNA).

Front 6

Messenger RNA (mRNA)

Back 6

a single strand of RNA that carries the information for making a protein

Front 7

Transfer RNA (tRNA)

Back 7

– a single strand of RNA that folds back on itself to form a specific shape. Each kind of tRNA bonds with only one kind of amino acid and carries it to the ribosome.

Front 8

Ribosomal RNA (rRNA)

Back 8

A globular form, is an important part of the structure of ribosomes and has catalytic functions needed during protein synthesis.

Front 9

• Translation

Back 9

Following transcription, the transcribed information in the mRNA is used to specify the amino acid sequence of a polypeptide.

Front 10

codon

Back 10

a sequence of 3 consecutive bases in mRNA

Front 11

a triplet codon

Back 11

• Because each codon consists of 3 nucleotides, the code is described as

Front 12

genetic code

Back 12

• The assignments of codons for amino acids and for start and stop signals are collectively called the

Front 13

• tRNA

Back 13

link with a specific amino acid and recognize the appropriate mRNA codon for that particular amino acid

Front 14

anitcodon

Back 14

o A particular tRNA can recognize a particular codon because it has a sequence of 3 bases, called the

Front 15

DNA --- mRNA --- tRNA --- codons --- polypeptide (protein) chain

Back 15

Overview:

Front 16

Start codon

Back 16

AUG, Met

Front 17

Reading frame

Back 17

The genetic code is read, one triplet at a time, from a fixed starting point that establishes this for the entire genetic message

Front 18

• Wobbble hypothesis

Back 18

– predicted by Crick. Is a breach of the base-paring rules. This hypothesis stated that there could be many acceptable forms of the same codons based on their differentiations in the base-pairing between tRNA and mRNA

Front 19

Antiparallel

Back 19

Whenever nucleic acid molecules associate by complementary base pairing, the 2 strands are antiparallel, meaning that the RNA or DNA being synthesized is moving in the 5’ to 3’ direction, while the DNA or RNA template is read in the 3’ to 5’ direction

Front 20

Upstream

Back 20

in an mRNA sequence, upstream is toward the 5’ end of the mRNA sequence or the 3’ end of the template DNA strand

Front 21

Downstream

Back 21

is toward the 3’ end of the RNA or the 5’ end of the template DNA strand

Front 22

Promoter

Back 22

In both bacteria and eukaryotes, the nucleotide sequence in DNA to which RNA polymerase and associated proteins initially bind

Front 23

Initiation

Back 23

RNA polymerase unwinds DNA double helix and initiates RNA synthesis

Front 24

Elongation

Back 24

Additional nucleotides are added to the 3’ end of RNA molecule. DNA double helix reforms following transcription

Front 25

Termination

Back 25

RNA polymerase recognizes termination sequence. RNA transcript and RNA polymerase are released.

Front 26

o Leader sequence

Back 26

mRNA has a noncoding leader sequence at its 5’ end

Front 27

o Start codon

Back 27

the start codon follows the leader sequence and signals the beginning of the coding sequence that contains the actual message for the polypeptide sequence

Front 28

o Stop codon

Back 28

At the end of each coding sequence, a stop codon signals the end of the protein

Front 29

trailing sequences

Back 29

o stop codons areThese are followed by noncoding 3’ ?

Front 30

mRNA and proteins

Back 30

• tRNA bridges the gap between

Front 31

Aminoacyl-tRNA synthetases

Back 31

amino acids are covalently linked to their respective tRNA molecules by enzymes which use ATP as an energy source

Front 32

aminoacyl-tRNA

Back 32

bind to the mRNA coding sequences to align the amino acids in the correct order to form the polypeptide chain

Front 33

P site

Back 33

the tRNA holding the growing polypeptide chain occurs here

Front 34

ribosomes

Back 34

The components of the transitional machinery come together at the

Front 35

A site

Back 35

the aminoacyl-tRNA that delivers the next amino acid in the sequence binds at this location

Front 36

E site

Back 36

where tRNA’s have delivered their amino acids to the growing polypeptide chain exit the ribosome

Front 37

the initiator tRNA

Back 37

Initiation:o The tRNA that bears the first amino acid of the polypeptide is

Front 38

initiation factors, which become attached to the small ribosomal subunit.

Back 38

initiation: o The initiation of translation uses proteins called

Front 39

o Elongation

Back 39

is a cyclic process in which amino acids are added 1 by 1 to the growing polypeptide chain. Elongation proceeds in the 5’ to 3’ direction along the mRNA. The polypeptide chain grows from its amino end to its carboxyl end.

Front 40

Termination

Back 40

occurs when the ribosome reaches one of the 3 stop codons. The A site bonds to a release factor, which triggers the release of the completed polypeptide chain and dissociation of the translation complex

Front 41

5’ cap

Back 41

is added to the 5’ end of the eukaryotic mRNA molecule.

Front 42

poly-A-tail

Back 42

The molecule may also have a _______of adenine-containing nucleotides added to the 3’ inch.

Front 43

exons

Back 43

• In mayn eukaryotic genes the coding regions, called

Front 44

introns

Back 44

are interrupted by noncoding regions, called

Front 45

pre-mRNA

Back 45

o Both exons and introns are transcribed, but introns are later removed from the original

Front 46

• Retroviruses

Back 46

viruses that synthesize DNA from an RNA template. In retroviruses the flow of genetic information is reversed by the enzyme reverse transcriptase

Front 47

o Base substitution

Back 47

may alter or destroy the function of a protein if a codon changes so that it specifies a different amino acid.

Front 48

o Frameshift mutation

Back 48

changes the codon sequences downstream from the mutation