topic 6 gene expression

Link between genotype and phenotype

Protein

Gene expression

Process that DNA directs protein synthesis

Two stages of gene expression

Transcription and translation

What did Archibald Garrod suggest

genes dictate phenotypes through enzymes

What did Archibald Garrod say about inherited diseases

its the inability of synthesize a certain enzyme

How do you cells synthesize and degrade molecules?

Metabolic pathways

one gene-one enzyme hypothesis later (one gene-one protein)

Each gene dictates production of a specific enzyme

Transcription

Synthesis of RNA using information in DNA

What does transcription produce?

mRNA

Translation

synthesizing proteins from mRNA.

Where does translation take place?

Ribosomes

What happens with translation and transcription in prokaryotes?

Translation can start before transcription has finished

What physically separates transcription from translation in eucaryotic cell

Nuclear envelope

What are the RNA transcripts in eucaryotic cells?

Modified through RNA processing

Primary transcript

Initial RNA transcript

Central dogma

Cells are governed by cellular chain of command

cycle of transcription and translation

DNA- RNA- Protein

How many amino acids are there?

20

How many nucleotides correspond to an amino acid

Three

What is the flow of information from a gene to a protein based on?

Triplet code

Triplet code

Series of non-overlapping three nucleotide words

what are words of a gene transcribed into

Complementary non-overlapping three nucleotide words of mRNA

What are mRNA words translated into?

chain of amino acids

Template strand

Provide a template for nucleotides in a RNA transcript

Are the template strands always the same for a given gene?

Yes

What are mRNA base triplets called?

Codons

During translation, how do you read codon

5' to 3' direction

What does each codon do?

codes for a specific amino acid

How many codons are there?

64, 61 for amino acids and 3 for stop

What is the start codon?

AUG

what are the stop codons

UAA, UAG, UGA

how must codons be read?

In the correct reading frame

If jeans are transplanted, can they still be transcribed and translated?

Yes

What's the first stage of gene expression?

Transcription

What is RNA synthesis catalyzed by?

RNA polymerase

RNA polymerase

Separates DNA strands and joins RNA nucleotides

Does RNA polymerase need a primer?

No

Promoter

DNA sequence where RNA polymers attaches

Terminator

Sequence signalling end of transcription

Transcription unit

Stretch of DNA that is transcribed

Three stages of transcription

Initiation, elongation, termination

Initiation of transcription

RNA polymerase attaches to start of gene and opens DNA up

Elongation of transcription

RNA polymerase builds RNA strand by copying DNA code

Termination of transcription

RNA polymerase stops at end of gene and releases RNA strand

What signals the star point of transcription

Promoters

Transcription factors

Mediate binding of RNA polymerase and initiation of transcription

Transcription initiation complex

Complete assembly of transcription factors, RNA polymerase II all bound to a promoter

TATA box

promoter element crucial for forming initiation complex

Elongation of RNA strand

RNA polymerase moves along DNA and un twists double helix

Rate of transcription in eukaryotes

40 nucleotides per second

where are nucleotides added to the RNA molecule

3' end

Termination of transcription in bacteria

Polymerous stops transcription at the end of terminator and mRNA can be translated as is

What enzyme transcribes the polyadenylation signal sequence in eukaryotes?

RNA polymerase II

How many nucleotides past the polyadenylation signal is the RNA transcript released?

10-35 nucleotides

RNA processing

Enzymes modify pre-mRNA (primary transcript)

What happens during RNA processing?

Both ends of primary transcript are changed

which ends of pre-mRNA mlecule is modified

both ends

What does the 5' end receive

modified nucleotide 5' cap

what does the 3' end receive

poly- A tail

Functions shared from the alteration of mRNA ends

Facilitate the export of mRNA to the cytoplasm,

Protect mRNA from hydrolytic enzymes,

help ribosomes attach to 5' end

introns

Non-coding regions

Exxon's

Eventually expressed and translated into amino acid sequences

RNA splicing

Removes introns and joins exons

What does RNA splicing create?

mRNA with continuous coding sequence

What is RNA slicing carried out by?

spliceosomes

spliceosome

proteins and nuclear ribonucleoproteins that recognize splice sites

what catalyzes RNAs of the spliceosome

splicing reactions

Ribozymes

RNA molecules that function as enzymes

example of Ribozymes

self-splicing RNA's remove their own introns

Three properties that allow RNA to function as an enzyme

Form three dimensional structure,

Some basis contain functional groups,

May hydrogen bond with other nucleic acid

Alternative RNA splicing

Gene encoding more than one polypeptide, based on which segments are treated as exons during splicing

What is greater the number of proteins and organism can produce or the number of genes

Number of proteins

What are domains?

discrete regions of proteins

What do individual axons code for?

domains in a protein

What does Exxon shuffling result?

Evolution of new proteins

What helps a cell translate mRNA into a protein

Transfer RNA (tRNA)

What does tRNA do?

Transfer amino acids to a polypeptide in a ribosome

What is carried at each end of a tRNA molecule

amino acid at one end and a anticodon on the other

What does the anticodon of tRNA do

Base pairs with codon of mRNA

tRNA molecules

Single RNA strand 80 nucleotides (cloverleaf)

Why does TNA have a three dimensional conformation

because of its hydrogen bonds (L shaped)

First step for accurate translation

Correct match between a tRNA and an amino acid

What is the correct match of a tRNA and amino acid catalyzed by?

aminoacyl-tRNA synthetase

Second step for accurate translation

Correct match between tRNA anticodon and mRNA codon

Wobble

Flexible pairing at the third base of a codon

What does a wobble allow?

Some tRNA to bind to more than one codon

what do ribosomes do

Facilitate specific coupling of tRNA anticodons with mRNA codon

What are the ribosome sub units made of?

rRNA and proteins

What do some antibiotic specifically target

Bacteria ribosomes without affecting eucaryotic ribosomes

Size of prokaryotic ribosomes

70s (50s and 30s subunits) with RNA 5s, 23s, 16s

eukaryotic ribosomes size

80s (60s and 40s subunitys) with RNA 5s, 5.8s, 28s, 18s

Three binding sites for tRNA

P site, A site, E site

p site

peptidyl-tRNA binding site

A site

aminoacyl-tRNA bindin site

E site

exit site

what does initiation bring together?

mRNA, TRNA with the first amino acid, two ribosome subunits

What happens first in initiation?

Small ribosome subunit binds with mRNA

What happens to the subunits after they bind with mRNA and initiated tRNA?

Move until it reaches start codon

What do initiation factors do?

Bring in the large subunit that completes the translation

Elongation of a polypeptide chain

Amino acids are added to proceeding amino acid at the C-terminus