1. Humans share most of the same protein families with worms, flies, and
plants
2. Hair grows by forming new cells at the base of the root. As they move
upward through the skin they are cut off from their nutrient supply and
start to form a hard protein called keratin in a process called
keratinization. As this occurs, the hair cells die. The dead cells and
keratin form the shaft of the hair.
3. Fingernails grow about three or four times as quickly as toenails
4. Each hair grows about 1/4 inch/month and grows for up to 6 years.
5. The most expressive muscles are the facial muscles. We need 17
muscles to smile and 43 muscles to frown.
6. The most numerous are the skeletal muscles. When we walk for
instance, we use 200 muscles.
Unit E Protein Synthesis
It is expected that students will…
•Demonstrate knowledge of the basic steps of protein synthesis,
identifying the roles of DNA, mRNA, and ribosomes in the processes
of transcription and translation. (p. 481-486)
•Determine the sequence of amino acids coded for by a specific DNA
sequence, given a table of mRNA codons. (p. 481)
•Give examples of two environmental mutagens that can cause
mutations in humans. (p. 490)
•Use examples to explain how mutations in DNA affect protein
synthesis and may lead to genetic disorders (p. 490)
_____ Adenine
_____ Anti-codons
_____ Central Dogma
_____ Code
_____ Codon
_____ Complementary Base
_____ Cytosine
_____ Elongation
_____ Endoplasmic reticulum
_____ Exocytosis
_____ Gene
_____ Gene mutation
_____ Genetic code
_____ Golgi body/Apparatus
_____ Guanine
_____ Helicase
_____ Histones
_____ Hydrolytic enzymes
_____ Initiation
_____ Initiation codon
_____ Messenger RNA (mRNA)
_____ Mutagen
_____ Mutation
_____ Peptide bonds
_____ Peptidyl Transferase
_____ Point mutation
_____ Polypeptide
_____ Polysome
_____ Protein
_____ Protein synthesis
_____ Ribosomes
_____ RNA Polymerase
_____ Template
_____ Terminator codon
_____ Thymine
_____ Transcription
_____ Transfer RNA (tRNA)
_____ Translation
_____ Triplets
_____ Uracil
_____ Vesicle
1. Structural: proteins help make up all structures in living things
Actin & Myosin: muscle proteins
Keratin: nails, hair,
horns, feathers
Collagen: bones, teeth, cartilage, tendon,
ligament, blood vessels, skin matrix
2. Functional: other proteins help us to keep our bodies
functioning properly and to digest our food.
Enzymes: lower the
energy of activation to
digest our food and to
assist in cellular
metabolism.
Hemoglobin
Protein structure is determined by the genetic code in
your DNA. The section of DNA that codes for one
gene
protein is called a
A gene is a section of
DNA that determines
the 10 sequence of amino
acids in a protein.
Therefore, the gene
determines the shape
and therefore, the
function of the
protein it codes for.
(rRNA)
If the process of protein synthesis were a play, these
would be the roles of all of the people involved
The director who has the master plan DNA (genes)
Three assistant directors mRNA, tRNA, rRNA
The cast Amino acids
The stage Ribosome
The stage crew Enzymes
Act One: Transcription
(Trans = across, cription = to write)
The coded message of a gene on DNA has specific instructions
on how to make each particular protein that our bodies need
The instructions from a gene are copied
from DNA to messenger RNA (mRNA)
in the nucleus
Then, the mRNA moves through the
nuclear pores and into the cytoplasm
where the proteins are made.
DNA
mRNA
A
U
T
A
C
G
G
C
The process of making mRNA is called TRANSCRIPTION
Watch the General Process
Step 1: Helicase unwinds the DNA (starting at the promoter).
Step 2: Complementary RNA base pairs attach to form the mRNA
strand
Step 3: RNA polymerase forms the RNA sugar-phosphate backbone
and checks for mistakes
Step 4: The RNA detaches & leaves the nucleus, & the DNA winds
back up
Take a closer look (how the RNA strand forms)
Act Two: Translation
 The mRNA code is made up of groups of three nucleotide
bases known as codons. Each codon codes for a specific
amino acid.
Eg. AGC = Serine
(see text fig. 25.7, p.481)
Eg. UGC = Cysteine
CAU?
AUG?
CUU?
GGC?
UGA?
AAA?
Why a Triplet Code?
It takes 3 nucleotides on the mRNA to code for 1 a.a.
Why? We must code for 20 different amino acids and there
are only 4 letters (nucleotides) in the alphabet.
With a single nucleotide, there are only 4 possible codes (41).
For two nucleotides, there are only 16 possible codes (42).
However, for three nucleotides there are 64 possible codes
(43), and that is enough to code for the 20 amino acids.
mRNA codon chart
(see text fig. 25.7, p.481)
Translation
•The written code (codons) on mRNA is ‘translated’ into a
specific amino acid sequence by ribosomes in the
cytoplasm.
•This is carried out with
the help of relatively
small transfer RNA
(tRNA) molecules.
A tRNA molecule is a small piece of RNA that has a
specific amino acid attached to it.
The tRNA also has a
special sequence of 3
nucleotide bases known
as an anticodon.
There is at least one type of tRNA for each of the 20 amino
acids.
As the correct amino acids are brought to the ribosome by the
tRNAs, they are joined together via dehydration synthesis to
form the protein that the original DNA coded for.
Please note that there is more than one codon for each
amino acid:
mRNA codons:
U C U
G C C
tRNA anti-codons:
A G A
C G G
SERINE
ALANINE
Why do you think that is?
The Steps of Translation:
1. The mRNA molecule moves through a pore in the nuclear
envelope and in to the cytoplasm. It joins with a ribosome
and is translated one amino acid at a time.
2. ‘INITIATION’: the first codon on any mRNA molecule is
called the ‘INITIATOR’. This codon is always AUG, which
codes for the amino acid methionine. This is a message to
START translation.
3. ‘ELONGATION’: the ribosome’s job is to position the
tRNA molecule onto the matching mRNA molecule.
This makes it possible for a peptide bond to be formed between
the amino acids attached to the tRNA molecules. These amino
acids chains make up the protein.
The enzyme that catalyzes this reaction is called PEPTIDYL
TRANSFERASE.
The 1st tRNA leaves, the ribosome moves over one codon, and
another tRNA brings the next amino acid.
Another peptide bond is formed, and the process continues for
the length of the mRNA strand.
4. TERMINATION: The last codon on any mRNA molecule
is called the ‘TERMINATOR’ codon, which is a message to
STOP translation.
This codon will be either UAA, UAG, or UGA. None of
these have a matching tRNA anticodon, so when no more
tRNA’s attach, the ribosome, protein, and mRNA detach from
each other.
What does translation look like?
CRACKING THE GENETIC CODE
DNA STRAND (one gene)
* Master Strand of DNA
A T G/T G C/G G C/G C T/T G A
T A C/A C G/C C G/C G A /A C T
codons
mRNA STRAND
A U G/U G C/G G C/G C U / U G A
tRNA STRAND
U A C/A C G/C C G/C G A/ A C U
anticodon
AMINO ACID SEQUENCE
Methionine---Cysteine---Glycine---Alanine---Stop
LET’S REVIEW…
•PROTEIN SYNTHESIS ANIMATION
http://www.pbs.org/wgbh/aso/tryit/dna/#
http://www.wisconline.com/objects/index_tj.asp?objID=AP1302
A BAD NIGHT AT THE THEATRE
Question: What if something goes wrong during translation?
Answer: MUTATION
•
A change in the
nucleotide
sequence of DNA
•
When the bases (‘letters’)
change, the wrong amino
acids are used to make
the protein.
•
The protein will NOT be
able to do its job.
There are 2 types of MUTATION:
1. Chromosomal mutations: a mutation of all or part of a
chromosome.
This usually involves MANY GENES, and therefore, MANY
PROTEINS.
Example: Down’s syndrome.
2. Gene mutations: a mutation that occurs within a gene at
some point along a chromosome. This mutation is only a
change of 1 or a few ‘letters’ (nitrogenous bases).
It usually only affects ONE GENE, and therefore, ONE
PROTEIN.
Example: Sickle cell anemia.