Download DNA.Protein.Synthesis Notes

Chapter 12: Protein Synthesis
What is DNA?
Chapter 13 Protein Synthesis - Overview
– The DNA of the gene is transcribed into RNA
• Which is translated into protein
• The flow of genetic information from DNA to RNA to
Protein is called the CENTRAL DOGMA
DNA
Transcription
RNA
Translation
Protein
Chapter 12 Protein Synthesis (Overview)
Central Dogma - FLOW IS FROM
DNA TO RNA TO PROTEIN
Chapter 13 Protein Synthesis (Overview)
FLOW IS FROM DNA TO RNA TO PROTEIN
• Genes on DNA are expressed through proteins, which provide
the molecular basis for inherited traits
• A particular gene, is a linear sequence of many nucleotides
– Specifies a polypeptide (long protein made of amino acids)
Chapter 12 Protein Synthesis (Overview)
Genes - discrete units of hereditary
information comprised of a nucleotide
sequence found in a DNA molecule.
12.1 RNA
Three Types of RNA
•
•
•
Messenger RNA (mRNA)
– carries copies of genes
(DNA) to the rest of the
cell.
Ribosomal RNA (rRNA) –
make up the ribosomes.
Transfer RNA (tRNA) –
transfers the amino acids to
the ribosomes as specified
by the mRNA
12-1 Messenger (mRNA)
1. Three main differences between mRNA
and DNA
•
•
•
Ribose instead of deoxyribose
mRNA is single stranded
mRNA has uracil in place of thymine (U
instead of T)
12.1 TRANSCRIPTION:
The process of making
mRNA from DNA
DNA
– Why do you need this
process?
• Location of DNA?
Nucleus
• Location of Ribosome?
Cytoplasm
Strand to be transcribed
T
A
C
T
T
C
A
A
A
A
T
C
A
T
G
A
A
G
T
T
T
T
A
G
U
A
G
Transcription
A
U
G
A
A
G
U
U
U
RNA
– mRNA takes code from
DNA in the nucleus to
Polypeptide
the cytoplasm
Start
condon
Stop
condon
Translation
Met
Lys
Phe
Transcription produces genetic messages in the
form of mRNA
12.1 In the nucleus, the DNA helix unzips
• And RNA polymerase lines up nucleotides along one
strand of the DNA, following the base pairing rules
– As the single-stranded messenger RNA (mRNA)
peels away from the gene
• The DNA strands rejoin
RNA nucleotides
RNA
polymerase
T C C A A T
A U C C A
T A G G T T A
Direction of
transcription
Newly made RNA
Template
Strand of DNA
Exon Intron
12.1 Eukaryotic mRNA is
processed before leaving the
nucleus
– Noncoding segments called
introns are spliced out leaving
only the coding exons
Exon
Intron
Exon
DNA
Cap
RNA
transcript
with cap
and tail
Transcription
Addition of cap and tail
Introns removed
Tail
Exons spliced together
mRNA
Coding sequence
• A 5’ cap and a poly A tail are
added to the ends of mRNA
• Cap and tail protect mRNA
Nucleus
Cytoplasm
5’
3’
T
C
C
A
A
U
C
C
A
T
A
G
G
T
Direction of
transcription
A
T
T
A
12-3 Protein Synthesis - Translation
• Translation is defined as going from mRNA
to protein
– tRNA which have amino acids attached are
going to the ribosome in the cytoplasm.
• What are amino acids? monomers of proteins
Amino acid
attachment site • Does the order of amino acids matter? Yes, they
must be in order for the protein to fold correctly.
Transfer RNA (tRNA) molecules serve as
interpreters during translation
– How does the correct tRNA (with amino acid
attached) bind to the mRNA? The tRNA contains
an anticodon which matches up with the mRNA
sequence (codon).
Amino acid
attachment site
Amino acid attachment site
Hydrogen bond
RNA polynucleotide chain
Anticodon
Anticodon
12.3 Translation
Ribosomes build polypeptides (proteins)
– A ribosome consists of two subunits
• Each made up of proteins and a kind of RNA
called ribosomal RNA
• Translation at Ribosome
tRNA
molecules
Growing
polypeptide
Large
subunit
mRNA
Small
subunit
12.3 Translation
– The subunits of a ribosome
• Hold the tRNA and mRNA close together during
translation
Met
Met
Large
ribosomal
subunit
Initiator tRNA
P site
U
A C
A U G
U
A C
A U G
Start
codon
1
mRNA
A site
Small ribosomal
subunit
2
Elongation adds amino acids to the polypeptide
chain until a stop codon terminates translation
– Once initiation is complete amino acids are added
one by one to the first amino acid
– The mRNA moves a codon at a time
• A tRNA with a complementary anticodon pairs with
each codon, adding its amino acid to the peptide chain
Figure out the exact sequence of amino acids needed
1. Take the DNA and transcribe it into mRNA
Example:
mRNA:
TAC ATA CTA GCG ACT
AUG UAUGAU CGC UGA
2. Take the mRNA sequence and decode it using
the codon chart.
AUG = MET
UAU = TYR
GAU = ASP
CGC = ARG
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