Chapter 17: Gene expression, from gene to protein

What is gene expression?

process by which DNA directs protein synthesis

What are the two stages of gene expression?

transcription and translation

What is transcription?

the synthesis of mRNA, using information stored in DNA

What is translation?

the synthesis of a polypeptide at a ribosome, using information in the mRNA

When does translation begin in prokaryotes?

translation can begin while transcription is not completed

When does translation begin in eukaryotes?

the nuclear envelope separates the two processes.

What happens to RNA transcripts before becoming RNA

modification

What is the genetic code?

collection of codons of mRNA, each of which directs the incorporation of a particular amino acid into a protein during protein synthesis

What is a codon?

a sequence of three nucleotides that together form a unit of genetic code in a DNA or RNA molecule.

What direction is RNA read?

5' to 3'

What strand of DNA is complementary to RNA?

the template strand

What strand of DNA has the same code as the DNA (minus T)

the coding strand

How many codons does the genetic code have?

64

What is the start codon and amino acid?

AUG (methionine)

There are three codons that do not code for an AA, what do they do?

they stop the translation

What does it mean for the genetic code to be universal?

that it has been operating very early in

history of life

What does RNA polymerase do?

t unwound the DNA molecule and catalyzes RNA nucleotide bonds, following base pairing with the template strand of DNA

Does RNA polymerase need a primer?

nope

Where does RNA polymerase attach?

promoter region (TATA box)

When does transcription end?

When it reaches the terminator in bacteria, or the poly-A tail in eukaryotes

What is the transcription unit?

the stretch of DNA that is transcribed

What are the three stages of transcription?

initiation, elongation, termination

What is initiation in translation?

Transcription factors recognize TATA box. Factors help RNA polymerase attach, forming the transcription initiation complex. RNA polymerase unwinds DNA

What happens in elongation?

RNA adds nucleotides to the 3' end of the growing RNA molecule.

Can a gene transcribed by several polymerases?

yes

What happens in termination in bacteria?

he polymerase stops at the end of the terminator.

What happens to the post termination mRNA in bacteria

The mRNA can be

translated without further modification.

What happen in eukaryotic transmission?

RNA polymerase II transcribed the polyadenylation signal

sequence

Where does the mRNA segment get terminated?

past the polyadenylation signal

What happens to eukaryotic pre-mRNA post transcription?

It gets processed before going to the cytoplasm

What happens to the 5' end of the pre-mRNA?

It receives a modified nucleotides 5' cap

What happens to the 3' end of the pre-mRNA?

It receives a Poly-A tail

What do the cap and tail do?

facilitate export to the cytoplasm, help ribosome to attach, and

protect against hydrolytic enzymes

What is an intron?

non-coding segment of RNA

What is an exon?

a coding segment of RNA

What does RNA splicing do?

remove introns.

What does a spliceosome do?

Cuts out introns in RNA splicing

How is it possible that one gene can code for several mRNA strands?

Because introns can be removed in different ways.

What is alternative splicing?

mRNA processing events that lead to different combinations of exons being spliced together

What are the primary components of translation?

tRNA and ribosomes

What does a tRNA do?

bind with a given amino acid at the 3' end

What does the tRNA anticodon do?

matches a give codon on the mRNA

What does aminoacyl-tRNA synthetase do?

matches a given tRNA with the corresponding amino acid

What happens to the amino acid after aminoacyl-tRNA synthetase?

it is charged and becomes more active

What do ribosomes do?

facilitate the coupling between tRNA anticodons and mRNA codons during protein synthesis

What are the components of ribosomes?

a large and a small subunit?

what are the ribosomal subunits made of?

proteins and rRNA (from nucleolus)

What are the three binding sites of tRNA

P site, A site, E site

What are the P, E, and A sites for?

P site holds active tRNA, A site holds next tRNA, E site discharges tRNA.

What does the small ribosomal subunit do?

binds with mRNA and a initiator tRNA

what is initiator tRNA?

The first transfer-RNA to come to the small ribosomal subunit..

What amino acid and codon does the initiator tRNA carry?

AUG (methionine)

What does the large ribosomal subunit do?

attaches and completes the translation initiation complex

Which tRNA can directly enter the p site?

initiator tRNA

What is elongation in translation?

Next amino acid is linked to the first one to make a chain

What is codon recognition?

Anticodon of incoming tRNA pairs with mRNA in A site

What end of the polypeptide is the AA added to?

C-terminus

What type of bonds are between the AA's

peptide bonds?

What is translocation?

Ribosome and mRNA moving relatively to each other

What direction does translation go?

5' to 3'

What is termination of translation?

A stop codon, of the mRNA enters the ribosome and the new protein is released from the ribosome

What does the release factor do in termination of translation?

enters the site A and causes the translation complex to come

apart and release the polypeptide

What is post-translational modification?

When certain proteins need additional changes in order to be functional, like being folded or transported

What is a signal peptide?

A short amino acid sequence on the end of a protein that is used for transport of the protein out of the cell.

What is a signal-recognition particle (SRP)

binds to the signal peptide and guides the

peptide to the endoplasmic reticulum membrane

Can many ribosomes work on the same mRNA?

yes

What is a mutation?

changes in the cell genetic information

What is a point mutation?

nucleotide pair change in a gene sequence

What can result from a point mutation?

production of an abnormal protein

What is nucleotide-pair substitution?

replaces one pair of nucleotides by another one

What is a silent mutation?

have no effect, redundancy of the genetic code

what is a missense mutation?

codes for an incorrect AA

what is a nonsense mutation?

codes from a stop codon

What is insertion and deletion?

addition / loss of several nucleotides usually creates a frameshift

mutation and deeply alter the structure of the protein

What is a frame shift mutation?

When a nitrogenous base is inserted or deleted.

How can a mutation occur?

during errors in DNA replication or due to the action of mutagens

What is a mutagen?

anything that causes a mutation