Hemophilia-

1. Caused by a defect in a single gene cannot produce all the proteins necessary for blood clotting

2. Depend on expensive injections of clotting proteins to prevent uncontrolled bleeding

flagellum

cytoplasmrough endoplasmicreticulum

ribosome

microtubules

lysosome

mitochondrion

Golgi complex

plasmamembrane

intermediatefilaments

vesicle

smooth endoplasmicreticulum

free ribosomevesicle

nuclear porechromatin (DNA)

nucleolusnuclear envelope

nucleus

Protein Synthesis

Gene

Expression

DNA, Genes & Proteins

The relationship of Chromosomes,

Genes, DNA & Proteins

Franklin's Legacy | PBSDNA to Protein

Genes and Proteins

Genes provide information to make proteins

Genetic information for protein synthesis is carried by RNA (ribonucleic acid) intermediates

The genetic code and codons

A sequence of nucleotide bases in DNA is translated into a sequence of amino acids in a protein.

Protein Synthesis Two-step process

Transcription and Translation 1. Transcription—nucleotide message sent from

nucleus to cytoplasm

a. DNA nucleotide sequence "copied" (using complementary base pairing) as a "messenger" nucleotide sequence of RNA (mRNA)

Transcription ofgene 1 produces an mRNA with a nucleotide sequence complementary to one of the DNA strands.

Translation produces a protein molecule with an amino acid sequence determined by the nucleotide sequence in the mRNA.

(a) TRANSCRIPTION

(b) TRANSLATION

messenger RNA

gene 1gene 3

gene 2

DNA

(nucleus)

protein

(cytoplasm)

Protein Synthesis

1. Transcription…b. RNA polymerase catalyzes synthesis of

mRNA; similar to DNA replication and DNA polymerase

• Promoter sequence binds RNA polymerase

• Termination signal is a sequence of nucleotides at end of genes that tell RNA polymerase to stop transcription

Transcription ofgene 1 produces an mRNA with a nucleotide sequence complementary to one of the DNA strands.

Translation produces a protein molecule with an amino acid sequence determined by the nucleotide sequence in the mRNA.

(a) TRANSCRIPTION

(b) TRANSLATION

messenger RNA

gene 1gene 3

gene 2

DNA

(nucleus)

protein

(cytoplasm)

Protein Synthesis

1. Transcription…c. The entire DNA molecule in a chromosome is

not transcribed, only a specific gene or family of genes is transcribed

(a) initiation

RNA polymerase

gene 1 gene 3gene 2

DNA

template strand

chromosome

(b) elongation

RNA

direction of transcription

RNA polymerase

DNA

beginningof gene

growingRNA

molecules

(a)

RNA polymerase

terminationsignal

RNA

(b)

Initiation, Elongation and Termination

Transcription ofgene 1 produces an mRNA with a nucleotide sequence complementary to one of the DNA strands.

Translation produces a protein molecule with an amino acid sequence determined by the nucleotide sequence in the mRNA.

(a) TRANSCRIPTION

(b) TRANSLATION

messenger RNA

gene 1gene 3

gene 2

DNA

(nucleus)

protein

(cytoplasm)

Protein Synthesis

2. Translation—nucleotide sequence of mRNA used to synthesize a sequence of amino acids (polypeptide or protein)

a. Occurs on the endoplasmic reticulum using ribosomes

0.5 micrometers

smooth endoplasmic reticulum

vesicles

ribosomes

rough endoplasmic reticulum

0.5 micrometers

Protein Synthesis

2. Translation…b. mRNA codons are used to specify amino acids

c. Ribosomes "read" mRNA codons to synthesize a specific amino acid sequence

(a) messenger RNA

A Codon = three nucleotide bases

tRNA/amino acid binding sites

(b)catalytic site

smallsubunit

largesubunit

ribosome (containsribosomal RNA)

Protein Synthesis

2. Translation…d. Each of the 20 amino acids has a specific

"carrier" transfer RNA (tRNA) that brings the amino acid to the ribosome

e. Complementary base pairing between the mRNA and tRNAs determines the amino acid sequence

(c) transfer RNA

attachedamino acid

anticodon

(c) transfer RNA

tRNA/amino acid binding sites

(b)

(a) messenger RNA

catalytic site

attachedamino acid

smallsubunit

largesubunit

anticodon

ribosome (containsribosomal RNA)

Protein Synthesis

2. Translation…f. Ribosomes need to recognize the beginning and

end of the mRNA message • 1) Initiation (start) codon: AUG (methionine)

• 2) Stop codons: UAA, UAG, UGA

amino acid

methioninetRNA

smallribosomalsubunit

initiationcomplex

A tRNA with an attached methionineamino acid binds to smallribosomal subunit, formingan initiation complex.

(a)

tRNA

mRNA

(b) The initiation complex bindsto the end of an mRNA andtravels along the mRNA untilit encounters an AUG codon.The anticodon of the tRNApairs with the AUG codon.

second binding sitecatalytic site

firstbindingsite

largeribosomalsubunit

The large ribosomal subunit bindsto the small subunit, with themRNA between the two subunits.The methionine tRNA is in the firstbinding site on the large subunit.

(c)

catalyic site

A second tRNA enters thesecond binding site. Itsanticodon pairs with the codonin the mRNA. The tRNAcarries an attached aminoacid.

(d)

peptidebond

(e) The catalytic site catalyzes the formationof a peptide bond that links the twoamino acids. Both amino acids are nowattached to the tRNA in the secondbinding position.

ribosome moves one codon to right

The “empty” tRNA is released andthe ribosome moves one codon to the right. The tRNA with the two amino acids is now in the first tRNA bindingsite. The second tRNA binding site is empty.

(f)

tRNA detaches

catalytic site

Another tRNA, with an anticodoncomplementary to the next mRNAcodon, enters the second bindingsite. This tRNA carries the nextamino acid to be added to the chain.

(g)

catalytic site

The catalytic site forms a peptidebond that attaches the new aminoacid at the end of the chain. Thechain of three amino acids is now attached to the tRNA in the secondbinding site. The empty tRNA in the first site will be released and the ribosome will move one codon to the right.

(h)

completed peptide

(i) Binding of tRNAs and formation ofpeptide bonds between amino acidscontinues until the ribosomes reachesa stop codon. No tRNA binds to stopcodons. Instead, protein “releasefactors” signal the ribosome to releasethe newly made protein. The mRNA isalso released, and the subunits separate.

stop codon

amino acid

init

iati

on

co

mp

lex

methionine tRNA

tRNA

mRNA

first binding site

large ribosomal subunit

second binding site

catalytic site

catalytic site

catalytic site

catalytic site

peptide bond

ribosome moves one codon to the right

tRNA detaches

completedpeptide

stop condon

smallribosomalsubunit

(a) (b) (c)

(d)

(g) (h)

(e) (f)

(i)

amino acids

anticodon

codon

gene in DNA(template strand)

(a)

(b)

(c)

(d)

mRNA(codons)

tRNA(anticodons)

protein(amino acids)

gene

Review Protein Synthesis

Two Major Steps of Protein Synthesis Transcription & Translation

Initiation, Elongation and Termination