Protein Synthesis

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Protein Synthesis

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.

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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)

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VOCABULARY
_____ 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
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Proteins Have 2 Main Functions

1. Structural proteins help make up all structures
   in living things

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2. Functional other proteins help us to keep
our bodies functioning properly and to digest our
food.
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Protein structure is determined by the genetic
code in your DNA. The section of DNA that codes
for one protein is called a
gene
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.
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Central Dogma of Biology
one gene
one type of protein
one function in the cell
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(rRNA)
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How Does Protein Synthesis Work?
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)
mRNA, tRNA, rRNA
Three assistant directors
The cast
Amino acids
The stage
Ribosome
Enzymes
The stage crew
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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
U
A
G
C
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(No Transcript)
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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
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(No Transcript)
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Take a closer look (how the RNA strand forms)
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TRANSCRIPTION
http//www.johnkyrk.com/DNAtranscription.html
TRANSCRIPTION GAME
http//library.thinkquest.org/20465/g_DNATranscrip
tion.html
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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
AUG?
CAU?
CUU?
AAA?
UGA?
GGC?
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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.
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mRNA codon chart
(see text fig. 25.7, p.481)
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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.

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A tRNA molecule is a small piece of RNA that has
a specific amino acid attached to it.
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Please note that there is more than one codon for
each amino acid
mRNA codons U C U G C C
tRNA anti-codons
C G G
A G A
SERINE
ALANINE
Why do you think that is?
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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.  
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1. ELONGATION the ribosomes 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.
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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.
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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 tRNAs attach, the ribosome, protein, and
mRNA detach from each other.
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What does translation look like?
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CRACKING THE GENETIC CODE
Master Strand of DNA
DNA STRAND (one gene)
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
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AMINO ACID SEQUENCE
Methionine---Cysteine---Glycine---Alanine---Stop
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TRANSLATION
http//www.johnkyrk.com/DNAtranslation.html
http//www.brookscole.com/chemistry_d/templates/st
udent_resources/shared_resources/animations/protei
n_synthesis/protein_synthesis.html
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LETS REVIEW

• PROTEIN SYNTHESIS ANIMATION
• http//www.pbs.org/wgbh/aso/tryit/dna/

http//www.wisc-online.com/objects/index_tj.asp?ob
jIDAP1302
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(No Transcript)
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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.

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There are 2 types of MUTATION

• Chromosomal mutations a mutation of all or part
  of a chromosome.
• This usually involves MANY GENES, and therefore,
  MANY PROTEINS.
• Example Downs syndrome.

• 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.