Protein Synthesis

Yes, it is still chapter 3!

It is the DNA in the nucleus that stores instructions for protein synthesis and this DNA is contained in chromosomes.

Human body cells contain 23 pairs of chromosomes.

Each chromosome contains DNA strands wrapped around special proteins called histones.

GeneThe functional unit of

heredity.Consists of all the triplets (3

bases that specify an amino acid) needed to produce a specific protein.

Protein SynthesisDivided into transcription and

translation.Transcription is the production

of RNA from a single strand of DNA.

Translation is the assembling of a protein by ribosomes, using information carried by RNA molecule.

Transcription

TranscriptionTakes place inside of the nucleus.A codon is 3 bases on the new RNA

strand. DNA RNA

G CC GA UT A

Step 1Begins when the enzyme RNA polymerase binds to the promoter of a gene.

Step 2Enzymes promote the synthesis of a mRNA strand using nucleotides complementary to those in the gene.

Step 3Continues until DNA stop signal is reached. The enzyme and mRNA detach and the complementary DNA strand reattaches.

TranslationOccurs in the ribosomes.Process of assembling

proteins from information carried by the mRNA molecule.

Step 1 Begins at the “start” codon of the

mRNA. Ribosome binds to the mRNA molecule

near the codon at the beginning of the messenger strand.

Joined by the first tRNA which carries the amino acid methionine (UAC).

Step 2Small and large ribosomal

subunits interlock around mRNA strand.

Second tRNA arrives at the next binding site of the ribosome.

Step 3Anticodon of second tRNA binds

to the next mRNA codon.

Step 4First amino acid is detached

from tRNA and joined to the next amino acid by a peptide bond.

First tRNA detaches as next arrives and attaches to mRNA.

Step 5Amino acid chain continues to

elongate until the stop codon is reached.

Components separate.As the chain of amino acids

develops, it folds into the unique shape of a functional protein molecule.

DNA mRNA –codon tRNA-anticodon

Amino acid

AAA

TAT

CCT

GGT

AGA

ATT

ATG

Anticodon Amino acid

AAA Lysine

AAU Asparagine

ACU Threonine

AGA Arginine

AUG Methionine

AUU Isoluecine

CAA Glutamine

CAU Histidine

CCU Proline

GAA Glutamic acid

GAU Aspartic acid

GCU Alanine

GGU Glycine

GUU Valine

UAA Stop codon

UAU Tyrosine

UCU Serine

UGG Tryptophane

UGU Cysteine

UUA Leucine

UUU Phenylalanine

1. Summarize in your own words the process of transcription.

2. Summarize in your own words the process of translation.

1. What is the function of DNA?2. Suppose that a DNA segment has

the following nucleotide sequence: CTC ATA CGA TTC AAG TTA. What is the nucleotide sequence that would be found in a complementary mRNA strand?

3. Summarize in your own words the process of transcription.