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Protein Synthesis

Consists of 2 main steps

Step 1: Transcription

Step 2: Translation

DNA

Central Dogma

Proteins

RNA

Occurs in the Nucleus

Translation

Occurs at the Ribosome

Transcription

Step 1

Step 2

DNA

RNA

Occurs in the Nucleus

Transcription

Step 1

What is RNA?

RNA is different from DNA in 3 ways

The sugar is

Ribose instead of deoxyribose

RNA is

Single stranded instead of double stranded

Thymine is replaced by

Uracil

Adenine

Uracil

In RNA

There is no Thymine

Adanine

bonds to

Uracil

A – U How to code DNA into mRNA

CGAUG

C

T

A

Let’s make an RNA strand

DNA

A

T

G

C

A

C

mRNA

U

A

G

G

C

U

Types of RNAMessenger

RNA (mRNA)Carry copies of instructions for the assembly of amino acids into proteinsServe as “messengers” from DNA to the rest of the cellRibosomal RNA (rRNA)Helps build ribosomesTransfer RNA (tRNA)Transfers the amino acid to the ribosome

There are 3 types of RNA

:

C10L10C12

Step 2

of protein synthesisTRANSLATION

During translation, the nitrogen bases of mRNA tell the cell which amino acids (building blocks of proteins) are needed to build a protein (polypeptide).

mRNA bases are read in groups of

3 called codons. Each codon codes for an amino acid.

Example:

RNA Strand: U C G C A C G

G

U

Reads as: UCG – CAC – GGU (3 codons)

Represents the amino acids:

Serine –

Histidine – Glycine

amINO

aCIDSThere are only 20 different amino acids, but

64

different codon possibilities, so several codons might represent

1

amino acid.

example:

UCU

,

UCC, UCA, and UCG all code for the amino acidSERINEThere is also one codon AUG that is called the START

codon because it starts protein synthesis.There are 3 stop codons that stop protein synthesis.

Lets practice

mRNA

AUG

UGA

CCU

Amino Acid

mRNA

GCG

GAU

UGC

Amino Acid

Second Base of Codon

First Base of Codon

U

C

A

G

Third Base of Codon

U

UUU

Phenylalanine

phe

UCU

Serine

ser

UAU

Tyrosine

tyr

UGU

Cysteine

cys

U

UUC

UCC

UAC

UGC

C

UUA

Leucine

leu

UCA

UAA

STOP

UGA

STOP

A

UUG

UCG

UAG

UGG

Tryptophan

trp

G

C

CUU

Leucine

leu

CCU

Proline

pro

CAU

Histadine

his

CGU

Arginine

arg

U

CUC

CCC

CAC

CGC

C

CUA

CCA

CAA

Glutamine

gln

CGA

A

CUG

CCG

CAG

CGG

G

A

AUU

Isoleucine

ile

ACU

Threonine

thr

AAU

Asparagine

asn

AGU

Serine

ser

U

AUC

ACC

AAC

AGC

C

AUA

ACA

AAA

Lysine

lys

AGA

Arginine

argAAUGMethionineMet (start)ACGAAGAGGGGGUUValinevalGCUAlaninealaGAUAspartic AcidaspGGUGlycineglyUGUCGCCGACGGCCGUAGCAGAAGlutamic AcidgluGGAAGUGGCGGAGGGGG

C10L10C12

AUG

START

Methionine

Lets practice

C10L10C12mRNA

AUG

UGA

CCU

Amino Acid

mRNA

GCG

GAU

UGC

Amino Acid

Met

(Start)

Stop

Pro

Cys

Asp

Ala

Translation

During translation the mRNA strand synthesized during transcription will be used to make a protein.

How is a protein (polypeptide) made?

The mRNA leaves the nucleus and attaches to a

ribosome

C10L10C12

Translation begins at the

START codon (AUG) on the mRNA.

The codons in mRNA match

anticodons

in

tRNA

.

TRNA transfers amino acids to the ribosome when they are called for by the codons in mRNA.

C10L10C12

How is a protein (polypeptide) made?

The ribosome moves down the mRNA strand, codon by codon, and each

tRNA brings an amino acid that is added to the growing protein (polypeptide).

C10L10C12

How is a protein (polypeptide) made?

C10L10C12