Protein
Synthesis
Importance of Proteins
• Much of the “work” done by the cells and tissues of the
body is actually the result of a protein.
• Examples include:
– Carrier proteins, which facilitate many forms of cell
membrane transport, including endocytosis.
– Recognition proteins, which identify the cell as self to the
immune system.
– Antibodies, which bind to and disable infectious viruses and
bacteria.
– Structural proteins, which make up connective tissues
such as ligaments and tendons.
– Hormones, which deliver messages throughout the body.
– Enzymes, which speed up the rate of chemical reactions
within the body.
• Enzymes usually end with –ase, and are a
necessary component of every form of chemical
change in the body, such as the steps of the Krebs
cycle.
• Proteins are
made of one or
more
polypeptides,
or chains of
amino acids.
• Insulin, a
protein
hormone that
helps regulate
blood sugar, is
made of two
polypeptides.
• Proteins form very
complex three-dimensional
structures that are directly
the result of their primary
structure, or sequence of
amino acids in their
polypeptides.
– A change of even a single
amino acid can alter the
entire shape of the protein.
DNA to RNA to Protein
• The nucleus is able to control the cell by
directing the amount and types of
proteins produced by the ribosomes in
the cytoplasm and rough endoplasmic
reticulum.
• This entire process is called protein
synthesis and begins with the DNA that
makes up the chromatin/chromosomes in
the nucleus.
• DNA is copied to RNA which goes into
the cytoplasm to make the protein
RiboNucleic Acid - RNA
DNA vs. RNA
Structure
Location
DNA
Deoxyribose
C=G
A = T
Double helix
Nucleus only
# copies
# types
One
One
Sugar
Bases
RNA
Ribose
C=G
A = U
Single strand
Nucleus &
cytoplasm
Many
Three (mRNA,
tRNA, rRNA)
Transcription - Making RNA
Location = Nucleus
Types of RNA
• Messenger RNA
• Transfer RNA
• Ribosomal RNA
Messenger RNA - mRNA
• carries copy of the DNA into the
cytoplasm
• Three bases make up a CODON
• Made in the nucleus
Transfer RNA - tRNA
transfers an amino
acid to the ribosome
as it is coded by the
messenger RNA
Ribosomal RNA - rRNA
Ribosomes are
made up of
several proteins
and a rRNA
Genetic Code or CODON
Codon = a group of three nucleotides on the
mRNA that specify a particular amino acid.
A three letter “word” that codes for a particular amino
acid.
(Anti-Codon = tRNA = complementary Bases)
UCGCACGGU
This sequence would be read three bases at a time
UCG-CAC-GGU
The codons represent the different amino acids
UCG-CAC-GGU
Serine-Histidine-Glycine
Transcription vs. Translation
Protein synthesis is broken down into two parts
Transcription
• mRNA is made from DNA
• Location = Nucleus
Translation
•
•
•
•
Proteins are synthesized
Location = cytoplasm at the Ribosome (rRNA)
tRNA brings amino acids to ribosome
mRNA is the pattern to follow
Transcription
Making a copy of DNA, called RNA, to go
out into the cytoplasm to make proteins
Starts at the promoters – specific base sequence on DNA
Translation
• Decoding of the mRNA and the
formation a new protein
Translation
Translation (cont.)
Translation (cont.)