Genes to Proteins Transcription and Translation DNA RNA Protein DNA contains genes which provide...

Genes to Proteins

Transcription and

Translation

DNA RNA Protein• DNA contains genes

which provide the information necessary to make proteins

• Different versions of the same gene result in different versions or amounts of a protein, and the differences in the protein result in different characteristics

Nuclearmembrane

Transcription

RNA Processing

Translation

DNA

Pre-mRNA

mRNA

Ribosome

Protein

Don’t let this happen to you!!

How does RNA (ribonucleic acid) differ from DNA (deoxyribonucleic acid)?

1. RNA has a sugar ribose2. DNA has a sugar

deoxyribose

3. RNA contains uracil (U)4. DNA has thymine (T)

5. RNA molecule is single-stranded

6. DNA is double-stranded

RNA

Transcription• The process that copies the message in a gene into a

messenger RNA (mRNA) molecule that will provide the instructions for making a protein molecule

• Started and controlled by an enzyme called RNA polymerase.– RNA polymerase binds to the DNA at a special point (start

signal)– RNA polymerase unwinds and separates the two DNA

strands– RNA polymerase adds and links complementary RNA

nucleotides as it “reads” the gene until it reaches a “stop” signal

RNA polymerase

mRNA

DNA

Transcription

1 Ribosomal RNA (rRNA) – Carrier molecule on ribosomes – holds the tRNA and mRNA in place

2 Transfer RNA (tRNA) - The molecule that physically couples nucleic acid codons with specific amino acids

3 Messenger RNA (mRNA) - The messenger that carries information from genes on DNA to the protein manufacturing ribosomes

Products of Transcription

TranslationThe process that makes proteins. The sequence of nucleotides in an mRNA molecule specifies the sequence of amino acids in a protein.

A U G G G C U U A A A G C A G U G C A C G U U

mRNA molecule

Codon= series of three nucleotides

This is a molecule of messenger RNA. It was made in the nucleus by transcription from a DNA molecule.

Messenger RNA (mRNA)

methionine glycine serine isoleucine glycine alanine stopcodon

protein

A U G G G C U C C A U C G G C G C A U A AmRNA

startcodon

Primary structure of a protein

aa1 aa2 aa3 aa4 aa5 aa6

peptide bonds

codon 2 codon 3 codon 4 codon 5 codon 6 codon 7codon 1

Each codon translates into one of twenty amino acids or is a stop or start signal

The Genetic CodeUUUUUCUUAUUG

CUUCUCCUACUG

AUUAUCAUAAUG

GUUGUCGUAGUG

UCUUCCUCAUCG

CCUCCCCCACCG

ACUACCACAACG

GCUGCCGCAGCG

UAUUACUAAUAG

CAUCACCAACAG

AAUAACAAAAAG

GAUGACGAAGAG

UGUUGCUGAUGG

CGUCGCCGACGG

AGUAGCAGAAGG

GGUGGCGGAGGG

Phenylalanine

Leucine

Leucine

Valine

Isoleucine

Methionine

Serine

Proline

Threonine

Alanine

Tyrosine

Stop

Histidine

Glutamine

Asparagine

Lysine

Asparagine

GlutamicAcid

Cysteine

Arginine

Serine

Arginine

Glycine

StopTryptophan

Note that 3rd Base Position is Variable

Eukaryotic Cell Protein SynthesisEukaryotic Cell Protein Synthesis

Protein Synthesis occurs on Ribosomes

A U G G G C U U A A A G C A G U G C A C G U U

A ribosome on the rough endoplasmic reticulum attaches to the mRNA

molecule.

ribosome

Protein Synthesis occurs on Ribosomes

Along comes a Transfer RNA Molecule…

amino acidattachment site

U A C

anticodon

methionine amino acid

A U G G G C U U A A A G C A G U G C A C G U U

The tRNA brings an amino acid to the first three bases (codon) on the mRNA.

Amino acid

tRNA molecule

anticodon

U A C

The three unpaired bases (anticodon) on the tRNA link up with the codon.

A U G G G C U U A A A G C A G U G C A C G U U

Another tRNA molecule comes into place, bringing a second amino acid.

U A C

C C G

Its anticodon links up with the second codon on the mRNA.

A U G G G C U U A A A G C A G U G C A C G U U

A peptide bond forms between the two amino acids.

Peptide bond

C C G

U A C

A U G G G C U U A A A G C A G U G C A C G U U

The first tRNA molecule releases its amino acid and moves off into the cytoplasm.

C C G

U A

C

A U G G G C U U A A A G C A G U G C A C G U U

C C G

The ribosome moves along the mRNA to the next codon.

A U G G G C U U A A A G C A G U G C A C G U U

Another tRNA molecule brings the next amino acid into place.

C C G

A A U

A U G G G C U U A A A G C A G U G C A C G U U

A peptide bond joins the second and third amino acids to form a polypeptide chain.

C C G

C C G

• The process continues.

• The polypeptide chain gets longer.

• This continues until a termination (stop) codon is reached.

• The polypeptide is then complete.A U G G G C U U A A A G C A G U G C A C G

U U

G U C

A C G

There is a tunnel through the large subunit of the ribosome that allows the growing polypeptide chain to pass out of the ribosome

• Termination of translation is triggered by stop codons

• A release factor enters the A site and triggers hydrolysis of the peptidyl-tRNA bond leading to the release of the protein.

Release of the protein causes the disassociation of the ribosome into its constituent subunits.

3’

5’

5’

3’

Transcription And Translation In Prokaryotes

Ribosome

Ribosome5’

mRNA

RNAPol.

Everything happens in the nucleus

DNA

Cytoplasm

Nucleus

Eukaryotic Transcription

ExportG AAAAAA

RNA

Transcription

Nuclear pores

G AAAAAA

RNAProcessing

mRNA

Eukaryotic Translation

Transcription/Translation Quiz

What is transcription? Production of RNA molecules by copying part of DNA into a complementary sequence of RNA

Why is transcription necessary?Transcription makes messenger RNA (mRNA) to carry the code for proteins out of the nucleus to the ribosomes in the cytoplasm.

Describe transcription.RNA polymerase binds to DNA, separates the strands, then uses one strand as a template to assemble mRNA. It uses the nucleotide bases except it replaces Thymine with Uracil

Transcription/Translation QuizWhat is translation?

The genetic message encoded in RNA is used to create a polypeptide with a specific amino acid sequence

Describe translation.The cell uses information from mRNA and tRNA to produce proteins.

Why is translation necessary?Translation assures that the right amino acids are joined together by peptides to form the correct protein.What are the main differences between

DNA and RNA?DNA has deoxyribose, RNA has ribose; DNA has 2 strands, RNA has one strand; DNA has thymine, RNA has uracil.