Transcript Protein Synthesis - OpotikiCollegeBiology

Protein Synthesis
Making proteins – one of the jobs
of genes.
Ribosomes
• Cell organelle that is the site of protein
synthesis.
• In the cytoplasm
• Linked by endoplasmic reticulum
• to vesicles that release/secrete the protein
the ribosome made.
Two problems –
location and structure
• The code for the protein is in the
chromosomes.
• The chromosomes are in the nucleus.
• How does the info get from the
chromosomes in the nucleus to the
ribosomes in the cytoplasm?
Two problems
location and structure
• The code is written in nucleotide bases
and proteins are built out of amino acids.
• How does the chromosome alphabet get
changed into structures that join up to
make proteins?
• Each group of 3 nucleotide bases in the
DNA is called a triplet.
• The triplet can’t leave the nucleus, so
another nucleic acid comes to the nucleus
to read it.
Transcription (using the same
code)
• This messenger is called mRNA.
• The three bases that match the DNA triplet are
called a codon.
• E.g DNA
•
mRNA
TGC GGA CCG GAG
ACG CCU GGC CUC
• Manual pg 85.
Translation
(changing to a new code)
• At the ribosome• The codon comes in and brings the code.
• The tRNA reads the codon and goes off to
get the right Amino Acid.
• The Amino Acids are linked together inside
the ribosome to form the protein.
• Manual pg 86, 87.
DNA is transcripted to
make messenger RNA
(mRNA)
mRNA is translated to
make a polypeptide
• How does the mRNA know when to start
and when to stop reading?
• Special codons that tell them
• Manual pg 71. The genetic code.
Polypeptides and proteins
• A long chain of amino acids is called a
polypeptide (many peptide bonds!).
• Sometimes a protein is made of several
polypeptides joined together. This will
require information from the same number
of genes.
• One chromosome has many genes in the
exon sections.
• Each gene codes for one polypeptide
chain.
• The group of genes that code for the
protein are called a transcription unit.
• Michael pg 84 introns and exons.
Whole picture
Manual pg 78.
Protein synthesis and Replication together
Manual pg 79.