Download Genes and Proteins

Hemophilia1. 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
nuclear pore
chromatin (DNA)
nucleus
nucleolus
nuclear envelope
flagellum
rough endoplasmic
reticulum
cytoplasm
intermediate
filaments
plasma
membrane
ribosome
lysosome
microtubules
smooth endoplasmic
reticulum
Golgi
complex
free ribosome
vesicle
mitochondrion
vesicle
Protein Synthesis
Gene
Expression
DNA, Genes & Proteins
The relationship of Chromosomes,
Genes, DNA & Proteins
 Franklin's Legacy | PBS
 DNA 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)
gene 3
gene 1
DNA
gene 2
(nucleus)
(a) TRANSCRIPTION
messenger RNA
(cytoplasm)
Transcription of
gene 1 produces an
mRNA with a
nucleotide sequence
complementary to
one of the DNA
strands.
protein
(b) TRANSLATION
Translation produces a protein
molecule with an amino acid
sequence determined by the
nucleotide sequence in the mRNA.
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
gene 3
gene 1
DNA
gene 2
(nucleus)
(a) TRANSCRIPTION
messenger RNA
(cytoplasm)
Transcription of
gene 1 produces an
mRNA with a
nucleotide sequence
complementary to
one of the DNA
strands.
protein
(b) TRANSLATION
Translation produces a protein
molecule with an amino acid
sequence determined by the
nucleotide sequence in the mRNA.
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
chromosome
DNA
gene 1
gene 2
(a) initiation
template strand
RNA polymerase
gene 3
(b) elongation
RNA
direction of
transcription
beginning
of gene
DNA
RNA
polymerase
growing
RNA
molecules
(a)
RNA polymerase
termination
signal
(b)
RNA
Initiation, Elongation and Termination
gene 3
gene 1
DNA
gene 2
(nucleus)
(a) TRANSCRIPTION
messenger RNA
(cytoplasm)
Transcription of
gene 1 produces an
mRNA with a
nucleotide sequence
complementary to
one of the DNA
strands.
protein
(b) TRANSLATION
Translation produces a protein
molecule with an amino acid
sequence determined by the
nucleotide sequence in the mRNA.
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
rough endoplasmic reticulum
ribosomes
0.5 micrometers
smooth endoplasmic reticulum
0.5 micrometers
vesicles
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
(b) ribosome (contains
ribosomal RNA)
catalytic site
large
subunit
tRNA/amino acid
binding sites
small
subunit
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
attached
amino acid
anticodon
(a) messenger RNA
(b) ribosome (contains
ribosomal RNA)
catalytic site
large
subunit
tRNA/amino acid
binding sites
small
subunit
(c) transfer RNA
attached
amino acid
anticodon
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
initiation
complex
methionine
tRNA
small
ribosomal
subunit
(a)
A tRNA with an attached methionine
amino acid binds to small
ribosomal subunit, forming
an initiation complex.
tRNA
mRNA
(b)
The initiation complex binds
to the end of an mRNA and
travels along the mRNA until
it encounters an AUG codon.
The anticodon of the tRNA
pairs with the AUG codon.
second binding site
catalytic site
first
binding
site
(c)
The large ribosomal subunit binds
to the small subunit, with the
mRNA between the two subunits.
The methionine tRNA is in the first
binding site on the large subunit.
large
ribosomal
subunit
catalyic site
(d)
A second tRNA enters the
second binding site. Its
anticodon pairs with the codon
in the mRNA. The tRNA
carries an attached amino
acid.
peptide
bond
(e)
The catalytic site catalyzes the formation
of a peptide bond that links the two
amino acids. Both amino acids are now
attached to the tRNA in the second
binding position.
catalytic site
tRNA detaches
ribosome moves one codon to right
(f)
The “empty” tRNA is released and
the ribosome moves one codon to the
right. The tRNA with the two amino
acids is now in the first tRNA binding
site. The second tRNA binding site
is empty.
catalytic site
(g) Another tRNA, with an anticodon
complementary to the next mRNA
codon, enters the second binding
site. This tRNA carries the next
amino acid to be added to the chain.
(h)
The catalytic site forms a peptide
bond that attaches the new amino
acid at the end of the chain. The
chain of three amino acids is now
attached to the tRNA in the second
binding site. The empty tRNA in the
first site will be released and the
ribosome will move one codon to
the right.
completed
peptide
stop codon
(i) Binding of tRNAs and formation of
peptide bonds between amino acids
continues until the ribosomes reaches
a stop codon. No tRNA binds to stop
codons. Instead, protein “release
factors” signal the ribosome to release
the newly made protein. The mRNA is
also released, and the subunits separate.
second binding site
initiation complex
amino acid
methionine
tRNA
(a)
small
ribosomal
subunit
tRNA
mRNA
catalytic
site
first
binding
site
(b)
(c)
catalytic
site
tRNA detaches
catalytic
site
large
ribosomal
subunit
peptide
bond
ribosome moves one
codon to the right
(d)
(f)
(e)
catalytic
site
completed
peptide
(g)
(h)
(i)
stop
condon
gene
(a)
gene in DNA
(template strand)
codon
(b)
mRNA
(codons)
anticodon
(c)
tRNA
(anticodons)
amino acids
(d)
protein
(amino acids)
Review Protein Synthesis
 Two Major Steps of
Protein Synthesis
Transcription &
Translation
 Initiation, Elongation
and Termination