Bio 122 Transcription and Translation

Genes vs. Proteins

Genes are nucleic acids, proteins are proteins

RNA

single-stranded nucleic acid that contains the sugar ribose
Bridge between DNA and protein synthesis
A,G,C,U

Transcription

synthesis of an RNA molecule from a DNA template
Carries message from DNA to protein machinery
(Nucleic acids same language, this copied)

Translation

The synthesis of a polypeptide using the genetic information encoded in an mRNA molecule. There is a change of language from nucleotides to amino acids.
Occurs at ribosomes

Prokaryote Translation

simultaneous transcription and translation

Eukaryote Translation

Transcription in nucleus, translation in cytoplasm

genetic code

4 nucleotides give rise to 20 amino acids
In triplets

template strand

The DNA strand that gets transcribed into RNA

Codons

Complementary groups of bases in mRNA that specifies an amino acid

codon table

shows all 64 codons with the amino acids they code for.

AUG

start codon

UAA, UAG, UGA

stop codons

redundancy

more than one codon can code for the same amino acid

no ambiguity

Each codon always codes for one specific amino acid

DNA to mRNA

transcription

RNA polymerase

pries the two strands of DNA apart and joins together RNA nucleotides complementary to the DNA template strand, thus elongating the RNA polynucleotide

Promoter

specific region of a gene where RNA polymerase can bind and begin transcription

terminator

A special sequence of nucleotides in DNA that marks the end of a gene. It signals RNA polymerase to release the newly made RNA molecule, which then departs from the gene

transcription unit

A region of DNA that is transcribed into an RNA molecule.

Three steps of transcription

initiation, elongation, termination

Initiation

the act of beginning
Details of the promoter
Extends several nucleotides upstream of starting point
Determines template strand

TATA box

A promoter DNA sequence crucial in forming the transcription initiation complex.

Transcription factor

Binds to TATA box
More join
Completes TIC
RNA synthesis begins

elongation (transcription)

RNA polymerase traverses the template strand and uses base pairing complementarity with the DNA template to create an RNA copy

Termination

RNA polymerase reaches a terminator sequence and detaches from the template
Ends right at sequence prokaryotic, eukaryotic continues a while after

Pre-RNA processing

After transcription, before translation

1) alterations of the ends

5' cap- attatches here for ribosomes prior to translation
3' tail- helps export mRNA to nucleus

2. RNA splicing

Cut and past portions of the molecule
Introns, non coding
Exons, coding
Introns cut out, exons are joined
MRNA ventures to cytoplasm

Translation with mRNA

Translated to from a protein

Transfer RNA

type of RNA molecule that transfers amino acids to ribosomes during protein synthesis
3' end- amino acid attachment
45 different as opposed to 61, anticodons recognize more than 1 codon due to wobble

anitcodon

a set of 3 nucleotides that is complementary to an mRNA codon

Ribosome large subunit

(P) - polypeptide chain grows
(A) - next amino acid to be added

small subunit

binds to mRNA

Initiation of Ribosome

Small subunit attatches to a tRNA, attatches to 5' end mRNA, start codon nearby, initiator tRNA attatches to initiation codon
Lg subunit competes complex formed by initiation factors and GTP
P site- initiator tRNA

Elongation in ribosome

Amino acids added to initial amino acid
Elongation factors and energy used in each addition

codon recognition

the anticodon of an incoming tRNA molecule, carrying its amino acid, pairs with the mRNA codon in the A site of the ribosome

peptide bond formation

second stage of elongation; peptide bonds form between amino acids that are linked to tRNAs in the P and A sites

Translocation

The process in which a segment of tRNA breaks off and ribosome advances

Termination in ribosome

Stop codon stops process, release factor frees polypeptide from RNA
Ribosome separates into large and small subunits

Transport vesicle

Moves polypeptides/ ribosomes to other parts of cell
Other ribosomes remain free