Protein Synthesis

Molecular Genetics:

BackgroundThe structure of DNA explains how DNA can be copied but it does not

explain how genes work.Genes are coded DNA instructions that

control the production of proteins within the cell.

What are proteins?•Chains of amino acids

•Amino acids (created based on the sequence of the nitrogen bases)

•Sequence of nitrogen bases => amino acids => proteins

Why are proteins important?1.Control biochemical pathways

2.Direct the formation of lipids, carbohydrates, and nucleotides

3. Responsible for the cell’s structure and movement

Before a protein can be put togetherit all starts with DNA.

ProblemDNA is inside of the nucleus but the

ribosomes that make proteins are in the cytoplasm.

It uses RNA!RNA takes the instructions to make

proteins to the Ribosome

How does DNA pass the instructions to

the ribosome?

DNA(nucleus)

RNA(cytoplasm)

Protein(ribosome)

transcription

translation

The Structure of RNA(Ribonucleic Acid)

•Single chain of nucleotides (1/2 of a ladder)•Sugar (ribose)•Phosphate group•Nitrogen bases (A,U, C, G)•3 types of RNA (mRNA, tRNA, rRNA)

mRNA (messenger)Carries the instructions (MESSAGE)for assembling amino acids into proteins.

mRNA

nucleus

linear

rRNA (ribosomal)• Proteins are assembled on

ribosomes.• Ribosomes made up of several

types of proteins, as well a type of RNA called rRNA (r = RIBOSOMAL).

globular

Pharm201 Lecture 2 2008 11

The Ribosome: Details• Complex of protein

and RNA• Small 30S subunit –

controls interactions between mRNA and tRNA

• Large 50S subunit – peptide transfer and formation of the peptide bond

tRNA (transfer)When a protein is being made,

tRNA molecules TRANSFER each amino acid to the ribosome as told by the specific coded message of

mRNA.

tRNA

Amino Acid

hairpin

Passing of Info from DNA to RNA is called

Process of copying a strand of DNAinto a complementary strand of RNA

Transcription

DNA RNA Proteins

Steps of Transcription1. DNA is copied into a strand of RNA inside of the

nucleus.A bonds with UracilC bonds with G

A

T

C

A

A

U

U

G

DNA RNA

RememberNO “T” in RNA

Draw diagram

2. mRNA leaves the nucleus and goes to the ribosomes

Transcription (continued)

Nucleus

mRNA

• Transcription Animation

• Protein Synthesis Interactive

TranslationTaking the instructions from mRNA and producing proteins

1.The mRNA arrives at the ribosome

2. tRNA (transfer RNA) brings free floating amino acids to the mRNA

3.The mRNA and tRNA match correct bases

4. The amino acids then bond to each other creating a protein chain

Nucleus

Ribosome

Nucleus

mRNACodon

anticodon

Amino acidtRNA

mRNA

tRNA

Protein

Codon

anticodon

Protein

Genetic CodeThe “language” of mRNA instructions iscalled the genetic code. RNA containsfour bases, A,U,G, & C. The code is written using 4 letters only.

There are 4 nitrogen bases, which combineto make 64 different codons, which make

20 different amino acids.

Genetic Code

AUGC= 64 codons = 20 amino acids

Codon = 3 nucleotides = 1 specific amino acid

RNA Strand = UCGCACGGU

This would be read 3 bases at a time

UCG – CAC - GGUThese codons represent amino acids

Serine – Histidine - Glycine

GCU

AAA

UCC

DNA vs. RNA

Transcription (elongation) (2)

/antisense strand