Chapter 14 - Gene Expression: From Gene to Protein

PCR

Method that creates many copies of a specific DNA sequence

Gel electrophoresis

Technique that separates DNA fragments by size using an electric current

DNA fingerprinting

Uses patterns of DNA fragment lengths to identify individuals

Restriction enzymes

Cuts DNA at specific nucleotide sequences, producing fragments with sticky or blunt ends

DNA sequencing

Determines the exact order of nucleotides in a DNA molecule

RNA vs DNA

strands, sugar, nitrogenous bases

• RNA has one strand, DNA 2

• RNA has ribose, DNA has deoxyribose

• RNA has uracil instead of thymine

what are the monomers of DNA and RNA? of proteins?

nucleotides, amino acids

Transcription

template: DNA

synthesizes: mRNA

location: nucleus

Translation

template: RNA

syntehsizes: polypeptide

location: ribosomes in the cytosol

central dogma

Genes program protein synthesis via genetic messages in the form of messenger RNA; DNA is transcribed into RNA, which is translated into RNA.

(DNA —→ RNA —→ protein)

how many amino acids are there?

20 amino acids

Which strand is used to produce an mRNA transcript

template strand

of the 64 possible codons, how many code for aminio acids?

61

What are the stop codons?

UAA, UAG, and UGA

what is the start codon?

AUG

why is the genetic code said to be redundant but not ambiguous

2 codons can code for the same amino acid but ONLY that amino acid

enzyme that uses the DNA template strand to transcribe a new mRNA strand

RNA Polymerase pries the 2 strands of DNA apart and joins together RNA nucleotides complementary to the DNA template strand

Which enzyme, DNA polymerase III or RNA polymerase, does not require a primer to begin synthesis?

RNA Polymerase

Why is the promoter area important in beginning transcription?

where RNA polymerase attaches to the DNA sequence and initiates transcription

what signals the end of transcription?

terminator

what is a transcription unit?

stretch of DNA downstream from the promoter that is transcribed into an RNA molecule

TATA box

DNA sequence in eukaryotic promoters that is crucial in forming the transcription initiation complex

In elongation of the RNA strand how is the DNA unwound?

RNA polymerase moves along the DNA template strand, joining complementary RNA nucleotides to the end of the growing RNA transcript

How does the termination of transcription occur in bacteria?

the transcribed terminator (an RNA sequence) functions as the termination signal, causing the polymerase to detach from the DNA and release the transcript

polyadenylation signal sequence (AAUAAA)

signal sequence in eukaryotes that ultimately ends transcription

after transcription, what happens during RNA modification?

• 5’ end: receives a cap

• 3’ end: enzyme forms a poly-A tail

three important functions of the 5ʹ cap and poly-A tail?

1. Facilitate the export of the mature mRNA from the nucleus

2. Help protect the mRNA from degradation by hydrolytic enzymes.

3. Help ribosomes attach to the 5’ end of the mRNA once it reaches the cytoplasm

introns vs exons

• introns: noncoding segments of nucleic acid that lie between coding regions

• exons: regions that are eventually expressed

spliceosomes

large complexes made up of proteins and RNA molecules that splice RNA by interacting with the ends of an RNA intron, releasing the intron and joining the 2 adjacent exons

alternative splicing 

allows a single gene to produce multiple different proteins

mRNA

Messenger RNA plays a crucial role in the flow of genetic information from DNA to proteins

• Transcription —→Transport —→Translation

tRNA

has a specific amino acid at one end of its 3D structure, while the other end is an anti-codon that can base-pair with the complementary codon on mRNA

rRNA

together with proteins, make up ribosomes; the most abundant type of RNA

anticodon

nucleotide triplet that base-pairs to a specific mRNA codon on the end of tRNA

describe the structure of a eukaryotic ribosome

consists of a large subunit and a small subunit, each made up of proteins and one or more rRNAs. In eukaryotes, the subunits are made in the nucleolus.

A site in ribosome

holds the tRNA carrying the next amino acid to be added to the chain

P site

holds the tRNA carrying the growing polypeptide chain

E site

where discharged tRNAs leave the ribosome

3 stages of translation

initiation, elongation, termination

3 key events that occur in elongation

1. codon recognition: anticodon of incoming tRNA base-pairs with mRNA in A site

2. peptide bond formation: rRNa molecule makes peptide bond between amino group in A site and carboxyl end of growing polypeptide in P site

3. translocation: ribosome moves tRNA from A site to P site, and empty tRNA in P site to E site at the same time, releasing the tRNA

what is a release factor

protein that binds directly to the stop codon in the A site that causes the addition of a water molecule instead of an amino acid to the polypeptide chain

3 types of post-translational modifications

1. Phosphorylation: adding phosphate groups that can alter protein’s function, activity, or location

2. Glycosylation: attaching sugar molecules to proteins, important for protein stability, folding, and cell-cell interactions

3. Proteolytic Cleavage: cleaving polypeptide chains into smaller fragments that can activate or deactivate