Chapter 16

Front 1

Template Strand

Back 1

The strand of DNA that is read by the enzyme during synthesis of RNA.

Front 2

Nontemplate Strand

Back 2

The strand of DNA that is not transcribed during synthesis of RNA. Its sequence corresponds to that of the mRNA produced from the other strand. Also called coding strand.

Front 3

Initiation (in transcription)

Back 3

The stage during which RNA polymerase and other proteins assemble at the promoter sequence.

Front 4

Sigma

Back 4

A detachable regulatory protein subunit that binds to polymerase before transcription can begin. Binds to the -10 and -35 boxes of a promoter, causing the DNA helix to open.

Front 5

Holoenzyme

Back 5

A multipart enzyme consisting of a core enzyme along with other required proteins. Formed from RNA polymerase and sigma.

Front 6

Core Enzyme

Back 6

The enzyme responsible for catalysis in a multipart holoenzyme. Contains the active site for catalysis and other required proteins.

Front 7

Promoter

Back 7

A short nucleotide sequence in DNA that binds RNA polymerase, enabling transcription to begin. In prokaryotic DNA, a single promoter often is associated with several contiguous genes. In eukaryotic DNA, each gene generally has its own promoter.

Front 8

Downstream

Back 8

The direction in which RNA polymerase moves along a DNA strand.

Front 9

Upstream

Back 9

Opposite to the direction in which RNA polymerase moves along a DNA strand.

Front 10

TATA Box

Back 10

A short DNA sequence in many eukaryotic promoters about 30 base pairs upstream from the transcription start site.

Front 11

Basal Transcription Factor

Back 11

General term for proteins, present in all cell types, that bind to eukaryotic promoters and help initiate transcription.

Front 12

Steps in initiating transcription in bacteria

Back 12

1. Sigma binds to promoter region in DNA.

2. Sigma opens the DNA helix and transcription begins.

3. Sigma is released and mRNA synthesis continues.

Front 13

Elongation (in transcription)

Back 13

The process by which messenger RNA lengthens. RNA polymerase moves along the template strand of DNA in the 3' to 5' direction syntehsizing RNA in the 5' to 3' direction until it reaches a termination signal.

Front 14

Termination (in transcription)

Back 14

The dissociation of RNA polymerase from DNA when it reaches a termination signal sequence. The transcribed RNA forms a hairpin, causing the RNA to separate from the RNA polymerase.

Front 15

Primary RNA Transcript

Back 15

In eukayotes,a newly transcribed messenger RNA molecule that has not yet been processed.

Front 16

Exon

Back 16

A portion of eukaryotic primary mRNA that is retained in the mature mRNA. They are expressed.

Front 17

Intron

Back 17

A portion of a eukaryotic primary mRNA that is removed by the spliceosome and is not part of the mature mRNA. The reason why eukaryotic genes are much longer than their corresponding mature RNA transcripts.

Front 18

Splicing

Back 18

The process by which introns are removed from primary RNA transcripts and the remaining exons are connected together.

Front 19

snRNPs (small nuclear ribonucleoproteins)

Back 19

Complexes of proteins and small RNA molecules that function in splicing as components of spliceosomes.

Front 20

Steps in how introns are removed from RNA molecules

Back 20

1. snRNPs bind to start of intron and key adenine ribonucleotide.

2. snRNPs assemble to form the spliceosome.

3. Intron is cut and a loop forms.

4. Intron is released and the exons join together.

Front 21

Spliceosome

Back 21

In eukaryotes, a large, complex assembly of snRNPs that catalyzes removal of introns from primary RNA transcripts.

Front 22

5' Cap

Back 22

Protect mRNA from degradation

Front 23

poly(A) tail

Back 23

In eukaryotes, a sequence of 100-250 adenine nucleotides added to the 3' end of newly transcribed messenger RNA molecules.

Front 24

Untranslated Regions (UTRs)

Back 24

The portions of the mRNA in front of and after the coding region.

Front 25

RNA Processing

Back 25

In eukaryotes, the changes that a primary RNA transcript undergoes in the nucleus to become a mature mRNA molecule, which is exported to the cytoplasm. Includes the addition of a 5' cap and poly(A) tail and splicing to remove introns.

Front 26

Polyribosome

Back 26

A structure consisting of one messenger RNA molecule along with many attached ribosomes and their growing peptide strands.

Front 27

Difference between transcription and translation in bacteria and eukaryotes

Back 27

Bacteria: transcription and translation occur simultaneously.

Eukaryotes: transcription and translation are separated in space and time.

Front 28

Transfer RNA (tRNA)

Back 28

One of a class of RNA molecules that have an anticodon at one end and an amino acid binding site at the other. Each tRNA picks up a specific amino acid and binds to the corresponding codon in messenger RNA during translation.

Front 29

Aminoacyl tRNA Synthetase

Back 29

An enzyme that catalyzes the addition of a particular amino acid to its corresponding tRNA molecule. Each amino acid has a different one.

Front 30

Aminoacyl tRNA

Back 30

A transfer RNA molecule that is covalently bound to an amino acid.

Front 31

Anticodon

Back 31

The sequence of three bases (triplet) in a transfer RNA molecule that can bind to an mRNA codon with a complementary sequence.

Front 32

Wobble Hypothesis

Back 32

Proposed by Francis Crick, the hypothesis that some tRNA molecules can pair with more than one mRNA codon, tolerating some variation in the third base, as long as the first and second bases are correctly matched.

Front 33

Ribosome Binding Site

Back 33

In a bacterial mRNA model, the sequence just upstream of the start codon to which a ribosome binds to initiate translation. Also called the Shine-Dalgarno sequence.

Front 34

Steps in initiating translation in bacteria

Back 34

1. mRNA binds to small subunit of the ribosome.

2. Initiator aminoacyl tRNA binds to start codon.

3. Large subunit of ribosome binds, completing ribosome assembly. Translation begins.

Front 35

Initiation Factors

Back 35

A class of proteins that assist ribosomes in binding to a messenger RNA molecule to begin translation.

Front 36

Translocation

Back 36

The process by which a ribosome moves down a messenger RNA molecule during translation.

Front 37

Elongation Factors

Back 37

Proteins involved in the elongation phase of translation, assisting ribosomes in the synthesis of the growing peptide chain.

Front 38

Steps in elongation of polypeptides during translation

Back 38

1. Incoming aminoacyl tRNA

2. Peptide bond formation

3. Translocation

Repeated down the length of the mRNA.

Front 39

Release Factor

Back 39

Proteins that can trigger termination of RNA translation when a ribosome reaches a stop codon.

Front 40

Steps in terminating translation in bacteria

Back 40

1. A release factor binds to the stop codon.

2. A hydrolysis reaction releases the polypeptide from the ribosome.

3. The ribosome subunits separate. The subunits are ready to attach to a new start codon.