From Gene To Protein

A PowerPoint presentation by Gene Tempest

Table of Contents Overview Transcription RNA Processing Translation Differences in protein Synthesis

Between Prokaryotes and Eukaryotes Point Mutations Bibliography

OverviewThe one gene-one polypeptide hypothesis

Main processes in protein production in eukaryotes:

1. Transcription

2. RNA processing

3. Translation

The synthesis of RNA under the direction of DNA

Actual synthesis of a polypeptide, under the direction of mRNA

Yields the finished mRNA

DNA RNA Protein

Animation 17.1

Triplet Code

Template Strand

Codon

Initiation Codon

Termination Codons

Terms

Series of three-nucleotide “words” that contain the instructions for making polypeptide chains.

The one out of the two DNA strands that is transcribed.

mRNA base triplet

AUG (also codes for amino acid methionine)

UAA UAG UGA

Fig. 17.3

Fig. 17.4

Note: Based on mRNA Codon

TranscriptionA closer look

RNA polymerase

Transcription unit

Promoter

Terms Transcription factors

Terminator

Pries the two strands of DNA apart and hooks together the RNA nucleotides, as they base-pare along the DNA template

Stretch of DNA that is transcribed into an RNA molecule

Region of DNA where RNA polymerase attaches and initiates transcription

In eukaryotes, a collection of proteins that mediate the binding of RNA polymerase and the initiation of transcription

RNA sequence that functions as the actual termination signal

Stages1. RNA polymerase unwinds the two DNA strands. RNA synthesis begins at the starting point on the template strand.

2. The RNA polymerase works its way “downstream”.

5’ 3’

3. RNA polymerase transcribes a terminator. RNA is released. RNA polymerase dissociates from DNA

Fig. 17.6

Animation 17.2

RNA ProcessingA closer look

RNA splicing

Introns

Exons

Terms snRNPs

Spliceosome

The removal of a large portion of the originally synthesized RNA molecule

Small nuclear ribonucleoproteins; joins with proteins to form the spliceosome

Eventually expressed--or translated into amino acid sequences

Non-coding segments of nucleic acid that lie between coding regions

Cuts at specific points to release the intron, then joins the two exons together

Stages1. The ends of each pre-mRNA molecule are modified:

- the 5’ end is capped off with a modified form of a guanine (G) nucleotide ( 5’ cap )

- a poly(A) tail, consisting of adenine nucleotides, attaches to the 3’ end

2. The spliceosome removes the introns and produces joined exons, now mRNA

Animation 17.3

TranslationA closer look

tRNA

Wobble

rRNA

Terms P Site

A Site

E Site

Transfer RNAFunction:to transfer amino acids from the cytoplasm to a ribosome Relaxation of the base-paring rules

Ribosomal RNAFunction:structural and catalytic role in ribosomes

Sites on the large ribosomal subunit

Holds the tRNA carrying the growing polypeptide chain

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

Exit for discarded tRNAs

StagesI. Initiation

1. Small ribosomal subunit binds to a molecule of mRNA2. A large ribosomal subunit complex completes it

II. Elongation 1. Codon Recognition

2. Peptide bond formation3. Translocation

III. Termination 1. The ribosome accepts a release factor instead of tRNA 2. The release factor hydrolyses the bond between tRNA and P site3. Ribosomal subunits dissociate

Animation 17.4

Differences between Prokaryotes and Eukaryotes

Can simultaneously transcribe and translate the same gene

Newly made proteins can diffuse to their sites of function

Nuclear envelope segregates transcription from translation

Have complicated mechanisms for targeting proteins to their appropriate destinations

Point MutationsChemical changes in just one or a few base pairs in a single gene

Substitutions

Insertions and deletions

Vocabulary

Missense Mutation

Nonsense Mutation

Frameshift Mutation

Replacement of one nucleotide and its partner in the complementary DNA strand with another pair of nucleotides

Addition or loss of one or more nucleotide pairs in a gene

The altered codon still codes for an amino acid

Alterations that change amino acids to a stop signal

Alters the reading frame of the genetic message

Bibliography

Campbell, Mitchell, Reece. “Biology Fifth Edition”. Illinois, USA. 1999

Biology Fifth Edition CD-ROM http://www.animationfactory.com http://occawlonline.pearsoned.com/

bookbind/pubbooks/campbell_awl/chapter17/deluxe.html