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Chapter 10
Protein Synthesis
DNA has the code to make proteins
• DNA contains the instructions for the cell:
– It tells it how to make copies of cells:
• Body (somatic) cells are copied by mitosis
• Sex cells are copied by meiosis
– It tells it how to make proteins which have many
functions in the cytoplasm of the cell.
Proteins are important
• Proteins make up genes, which determine
your genetic traits (hair color, height, etc.)
• Proteins act as catalysts to speed up chemical
reactions.
• Proteins direct the chemical reactions in your
cells and “tell the cell organelles” what to do.
• IN SUMMARY – Proteins are the instructions
of the DNA in action.
DNA review
• Nucleic acids are made up of monomers of
units called nucleotides:
Sugar, phosphate and base
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•
•
•
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DNA sugar is DEOXYRIBOSE
There are two strands in DNA (the two sides)
The bases in DNA are : A,T,C,G
AG are purines, CG are pyrimidines
DNA NEVER LEAVES THE NUCLEUS
RNA is a little different
• RNA is a single strand
• R stands for RIBOSE which is the sugar.
• There are two kinds of RNA:
– mRNA which is formed in the nucleus
– tRNA which is in the cytoplasm
• The bases of RNA are : C,G and A, U (not T)
• mRNA LEAVES the nucleus and goes to the
ribosome where protein synthesis occurs.
Protein synthesis is a series of STEPS
• 1. mRNA gets instructions from DNA
– This is called TRANSCRIPTION
• 2. mRNA leaves the nucleus and takes the
instructions to the ribosome.
• 3. mRNA gives the message to the t RNA
– This is called TRANSLATION
The tRNA attaches AMINO ACIDS together to FORM
PROTEINS
– This is called Protein Synthesis
• 4. PROTEINS coil up to form shapes that can act
as enzymes and bond with substrates.
STEP 1 – called TRANSCRIPTION
A. DNA uncoils when an enzyme tells the DNA
to unwind. This creates a REPLICATION FORK
B. The RNA POLYMERASE puts the mRNA
nucleotides together along the DNA strands,
adding the complementary bases and
proofreading them.
Step ONE
Step 2
• mRNA leaves the nucleus and takes the
instructions to the ribosome.
Step 2
Step 3
A. mRNA gives the message to the t RNA
This is called TRANSLATION
B. The tRNA carries Amino Acids on it (every 3
bases on tRNA has an amino acid attached these are called CODONS)
C. The tRNA attaches AMINO ACIDS together to
FORM PROTEINS
This is called Protein Synthesis
TRANSLATION
tRNA with amino
acid attached
Protein formed
from amino
acids
mRNA template
Step 4: The Protein then coils up
The protein then can do its job
• Like catalyze (speed up) reactions when acting
as an enzyme:
products
Reactant
Substrate
Enzyme
Catalyst
ACTIVE SITE
THE “CODE”
• The code for the tRNA to use to attach the
amino acids together into the protein strand is
found on the mRNA base sequence.
• Three bases make up the base sequence.
• The three bases are called the CODON.
• Scientists use tables to determine the correct
match of codon to amino acids.
• There are 21 amino acids in the body.
Table found in Ch. 10
Second nucleotide
Another type of codon table