Protein SynthesisBiology 11 preAP

Overview and Application

Try This!

1) One strand of DNA has the following sequence: T A C C G A C G G

What is the corresponding sequence of RNA?

2) If this new RNA is transported out of the nucleus directly to a ribosome, which of the three types of RNA is it?

OverviewMolecular Biology’s central dogma: replication, transcription, translation,

assembly: Howard Hugh’s Medicalhttp://www.youtube.com/watch?v=D3fOXt4MrOM

It is expected that you will know: The key terms gene expression, transcription, and

translation. How to explain the process of transcription How eukaryotic cells modify RNA after transcription The steps to translation How point mutations can change the amino acid

sequence

Overview

What are the stages of Protein Synthesis?

1) Transcription

2) mRNA Processing and Modification

3) Translation

Transcription

DNA is used as a template to form a molecule of single-stranded mRNA (messenger RNA)

http://vcell.ndsu.nodak.edu/animations/transcription/movie.htm

Transcription

Three steps:1) DNA unzips

2) Complimentary base pairing of ribonucleotides

3) Termination

Transcription – 1) Unzip

One section of DNA is unzipped (H-bond between nitrogen bases are broken) when RNA polymerase attaches to the promotor region of the DNA with the assistance of transcription factors.– Transcription Initation Complex

The DNA continues to be unzipped by RNA polymerase

Transcription – 2) Complimentary

RNA polymerase attatches free-floating ribonucleotides in the 5’-3’ direction – temporarily hydrogen bond with their complimentary

nucleotides on the DNA transcription unit– Covalent bond to the 3’ end of the previous ribonucleotide

Only one of the DNA strands is used as the template. Ex: DNA – A T C G

RNA –

Transcription - Termination

RNA polymerase reaches terminator sequence RNA polymerase detaches from DNA,

releasing single-stranded RNA strand DNA rewinds into its double helix

mRNA Processing

http://vcell.ndsu.nodak.edu/animations/mrnaprocessing/movie-flash.htm

Addition of 5’ cap Addition of poly-A tail RNA splicing

– Introns are removes, exons are spliced together by an enzyme called spliceosome

This enzyme has small nuclear RNA (snRNA) to help it work and is therefore referred to as a riboenzyme

Modified mRNA is transported out of the nucleus

Significance of mRNA splicing…

We have fewer than 25000 genes to make ~100000 proteins!– One gene can make different proteins due to

alternative mRNA splicing.

Translation

mRNA goes to the ribosome and is used as a template to synthesize a protein molecule.

http://vcell.ndsu.nodak.edu/animations/translation/movie.htm

Translation

Three Steps:

1) Initiation

2) Elongation

3) Termination

Translation – 1) Initiation

need start codon AUG

The first tRNA, with anticodon UAC and amino acid methionine temporarily binds to the first site

Translation – 2) Elongation

The second tRNA molecule attaches to the second site of translation.

Translation – 2) Elongation

The amino acid from the first tRNA is transferred to the amino acid on the second tRNA.

Translation – 2) Elongation

The first tRNA exits, the ribosome moves, a new tRNA enters, and the process is repeated.

Translation – 2) Elongation

The process is repeated many times, and a peptide, or strand of amino acids, is formed.

Translation – 3) Termination

The release factor enters.

Translation, or protein synthesis, ends.

Translation – 3) Termination

The completed polypeptide is released.

Translation - Application

What does this diagram represent?

- Translation

- ELONGATION

Polyribosomes

Many ribosomes transcribing the same mRNA

Very efficient!

Destination of Proteins

How does a protein “know” whether it to be used for a function in the cell, or bound for secretion?– Signal peptide: the first ~20 amino acids directs the

final destination

Application – table of mRNA codons (p 511)

Application

Consider the following DNA base sequence read from left to right:

T A C G C A A A A T G G

Determine the amino acid sequence that results from this DNA strand.

Application

DNA sequence:T A C G C A A A A T G G

mRNA sequence:A U G C G U U U U A C C

Animo acid sequence:

methionine – arginine – phenylalanine – threonine

Application

Which of the following is an anticodon of a molecule of tRNA carrying glycine?

A. G G A

B. C C U

C. C C T

D. C G C

Application

Which of the following is an anticodon of a molecule of tRNA carrying glycine?

Amino acid: glycine

mRNA codon: GGU/GGC/GGA/GGG

tRNA anticodon: CCA/CCG/CCU/CCC

Application

Which of the following is an anticodon of a molecule of tRNA carrying glycine?

A. G G A

B. C C U < ANSWER!C. C C T

D. C G C

Mutation Definitions

point mutation:– A change in the sequence of a base pair within a

gene

1) Base-pair substitutionA. Missense mutation – still amino acid

B. Nonsense Mutation – code for stop

2) Insertion and deletion – can cause frameshift mutation!

Definitions – Gene Mutations

frameshift mutationsTHE CAT ATE THE RAT – what if the “C” was deleted?

– The original DNA coded for which amino acids? DNA: TAC GGT TAG mRNA: AUG CCA AUC amino acids: methionine – proline - isoleucine

– The mutated DNA now codes for which amino acids? DNA: TAC CGG TTA G mRNA: AUG GCC AAU C animo acids: methionine – alanine - asparagine

Definitions - Gene Mutation

What effect does changing the amino acids have on the protein product?– Changes the shape.

Since shape determines function, it alters how the protein will function.

Proteins: Shape determines Function!

Definitions - Gene Mutation

Which has the potential for the most damage, deletions or subsitituations?

– Deletions! Frameshift

Definitions

Mutagens– Environmental influences that cause mutations

– Examples:Radiaton: radioactive elements, ultraviolet (UV) light, X rays

Organic chemicals: cigarette smoke, pesticides

Any Questions?

Closing

http://vcell.ndsu.nodak.edu/animations/transcription/movie.htm http://vcell.ndsu.nodak.edu/animations/translation/movie.htm http://vcell.ndsu.nodak.edu/animations/mrnaprocessing/movie-flash.htm

Molecular Biology’s central dogma: replication, transcription, translation, assembly: Howard Hugh’s Medicalhttp://www.youtube.com/watch?v=D3fOXt4MrOM

Epic:http://www.youtube.com/watch?v=u9dhO0iCLww