PROTEIN SYNTHESISFrom gene to protein

How does information get from DNA to proteins?

DNA:nucleotides are the monomersProteins: amino acids are the monomersDNA:in the nucleusProteins:synthesized in cytoplasm

Overview

DNA -mRNA-Protein = gene expression-central dogma of biology-a section of DNA's code (a gene) is copied

(transcribed) onto mRNA.-mRNA carries the code to the ribosome

where the code is translated, with the help of tRNA, into a sequence of amino acids (polypeptide)

The genetic code

-three bases on DNA = triplet-code for three bases on mRNA = codon-codes for one amino acid

Transcription details

- occurs in nucleus- purposes is to produce a copy of DNA

called messenger RNA which carries genetic information to the cytoplasm.

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Transcription: initiation

-One strand of DNA acts as template- RNA polymerase binds to promoter region

which includes the initiation site on a section of DNA (gene)

Elongation

- RNA polymerase moves along the DNA strand unwinding and unzipping, separating the strands by breaking the hydrogen bonds.

- the mRNA strand grows. It is complementary to the DNA template

Termination

- transcription continues until a termination site is reached

-mRNA strand is released

TranscriptionWatch video clip:

http://youtu.be/WsofH466lqk

Complete questions in notes and go over

Triplet codon system

- triplet = 3 bases on DNA- codon= 3 bases on mRNA- codes for a specific amino acid. One of

twenty possible amino acids. Redundancy built into system. 64 possible codons

- universal code since it used by all organisms

-stop and complete questions/ go over

Translation

- purpose is to translate info on mRNA into a chain of amino acids that fold into a functional protein.

- one gene codes for one protein

Ribosomes structure & function

- ribosomes have two subunits made up of protein and RNA

- site of attachment of mRNA and tRNA -site of protein synthesis

Transfer RNA

- a folded strand of RNA with a site for amino acid to attach at one end.

- the other end has three bases exposed which complement with an mRNA codon

- called an anticodon

Transfer RNA and ribosomes

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Translation details

- initiation- elongation- termination

Initiation

- mRNA attaches to small ribosomal subunit- start codon AUG- tRNA carrying amino acid methionine pairs

with codon AUG (anticodon UAC on tRNA)- large ribosomal subunit sandwiches mRNA-2 codon sites on ribosome "P" & "A"- "P" site occupied, "A" site empty

initiation

Elongation

- a second tRNA with an anticodon moves into the "P" site

- covalent peptide bond forms between a.a of "A" site and a.a of "P" site.

-"P" site tRNA breaks away to get another a.a

- ribosomal complex shifts along mRNA to next codon. Process continues, polypeptide grows

Elongation

Termination

- elongation continues until a "stop" codon is reached

- UAA, UAG, UGA- release factor ( a special protein) binds to

the A site.- the polypeptide is released and the

ribosome separates into the large and small subunits

Termination

Protein synthesis Video

http://youtu.be/5bLEDd-PSTQComplete questions 1-3