Making Proteins

Protein Synthesis

Cell Structure(80% of cell membrane is proteins)Transport Channels

Cell ProcessingHormones (signals)Enzymes

What else?

Why do we need protein synthesis?

1. DNA• Is the template for making mRNA during

transcription

2. RNA mRNA =messenger RNA

Makes and takes copy DNA to cytoplasm

What do we need for Protein Synthesis?

tRNA = transfer RNA Matches with mRNA on ribosomes Carries Amino Acids

rRNA = ribosomal RNA Part of ribosome Reads mRNA Directs tRNA

3. RibosomeReads mRNADirects tRNACreates peptide bonds between AA’s

4. Amino Acids (AA’s)Building blocks of proteins (20 AAs essential)Protein = AA chain = polypeptide chain

ORDER MATTERS!

AA order determines f(x) of protein

Protein Synthesis Overview

http://www.columbia.edu/cu/biology/courses/c2005/images/animtransln.gif

TRANSCRIPTION: writing the message

DNAmRNA

STEPS:1. unwind DNA in nucleus with help of

enzyme2. DNA polymerase pairs RNA

nucleotides with DNA nucleotides =mRNA

* U replaces T in RNA *

2 main steps of Protein Synthesis

3 DNA nucleotides (triplet)

m RNA CODON

Codons

Start Codon

2 main steps of Protein Synthesis

TRANSLATION: mRNA tRNA Protein (AA chain)

Steps:1. mRNA leaves nucleus and binds

to ribosome 2. tRNA (anticodon) brings the

amino acid to the mRNA (codon) on ribosomes

3. Ribosomes move down mRNA to next codon

4. tRNA anticodon brings and attaches next AA with peptide bond

5. tRNA leaves ribosome once AA attached

6. Repeat above steps to add AA until STOP CODON to signal end of protein

UAG, UAA, or UGA7. Polypeptide chain releases from

ribosomes

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

This is a molecule of messenger RNA.

It was made in the nucleus by transcription from a DNA

molecule.

mRNA molecule

codon

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

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

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

Amino acid

tRNA molecule

anticodon

U A C

A transfer RNA molecule arrives.

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

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

The polypeptide chain gets longer.

G U C

A C G

The process continues.

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

The polypeptide is then complete.

Synthesis PracticeDNA : A=T and C=GRNA: A=U and C=G *So, when transcribing DNA into

RNA “T” is replaced with “U”

Example:Original DNA: ATCGComplementary DNA: TACG

Transcription example:Original DNA: ATCGMessenger RNA: UACG

(CODON)

Translation Example: Messenger RNA: UACG

(CODON)Transfer RNA: AUGC

(ANTICODON)

tRNA brings the AA so they can bond to make protein

Practice Continued

DNA(triplet)

mRNA (codon)

tRNA(anti-codon)

TAC

GGA

CCT

TAT

ACT

Synthesis Practice

AUG (start)

CCU

GGA

AUA

UGA (stop)

UAC

GGA

CCU

UAU

ACU

Use mRNA codon and use the Universal Genetic Code Chart.AUG (codon)

A = 1st base U = 2nd baseG = 3rd base

To determine the AA