Download Nucleic Acids and Protein Synthesis Power Point

Nucleic Acids
and
Protein Synthesis
Nucleic Acids
 DNA

Deoxyribonucleic Acid
 RNA

Ribonucleic Acid
DNA
Double
stranded helix
Never leaves the nucleus
Watson, Crick, Wilkins
won Nobel Prize in 1962
Franklin died in 1958
never recognized
DNA
Nucleotide

Building Blocks of nucleic acids are
NUCLEOTIDES!
 Phospate group
 Sugar molecule (deoxyribose)
 Nitrogenous bases
Nitrogenous Bases of DNA
How do the N-Bases pair up?
A-T (2 bonds)
 G-C (3 bonds)

How Does DNA Replicate?
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1. double helix unwinds
2. Each chain serves as a template for new
nucleoide chain
3. point at which 2 chains separate is called the
REPLICATION FORK.
4. HELICASE = the enzyme that separates the
chains (breaks H bonds)
5. DNA POLYMERASE moves along the chains and
helps assemble new nucleotides forming new chains
(3’ to 5’ ONLY)
DNA LIGASE – ligates 5’ to 3’ (DNA polymerase
brings the nucleotides)
DNA replication continue…
The 3’ sugar has an –OH GROUP
 The 5’ sugar has a PHOSPHATE GROUP

LEADING STRAND – formed from 3’-5’
 LAGGING STRAND – formed from 5’- 3’
with the help of DNA LIGASE!
 OKAZAKI FRAGMENTS – fragments that
will be ligated together
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Can you see how DNA is making
an exact copy of itself!
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This a little more difficult
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Can you figure out the diagram?
Simplest Illustration of DNA
replication…
What is a

mutation??
A CHANGE in the
nucleotide sequence at
even ONE location!!
Protection
 About
1 in a billion nucleotides in
DNA is INCORRECTLY paired.
 DNA polymerase proofreads and
removes nucleotides that base pair
incorrectly.
 DNA polymerase & DNA ligase 
also repair damage caused by
ultraviolet light, xrays, and toxic
chemicals
Archibald Garrod
1909 English Physician
Suggested that genes dictate phenotypes
through enzymes, the proteins that
catalyze chemical processes in the cell
 GENOTYPE  genetic make up
 PHENOTYPE  physical appearance
 DNA –(transcription) RNA –
(translation) protein synthesis
 Genotype ------ phenotype

Garrod 1900’s
Children -> defect in 2 a.a. due to defect in
the enz. That helps make the a.a
 Phenylalanine->PKU
 Tyrosine ->albinism
 Geneenzymeamino acid (can’t be
made)
 Couldn’t prove it due to lack of technology

George Beadle & Edward Tatum
1940’s American Geneticists
ONE GENE ONE ENZYME (polypeptide)
HYPOTHESIS: the function of a gene is
to dictate the production of a specific
enzyme.
 Experimented with bread mold  lacked
an enzyme in a metabolic pathway that
produced some molecules that mold
needed to produce an amino acid called
arginine.

Tatum & Beadle 1958 Nobel Prize
Proved Garrod correct
 Bread mold -> can make all of it’s own a.a.
that it needs
 Gene -> enzyme -> amino acid
 One gene = enzyme
 One gene = one protein!!

RNA
RIBONUCLEIC ACID
 SINGLE
STRANDED
 RESPONSIBLE
FOR BRINGING
THE GENETIC INFO. FROM THE
NUCLEUS TO THE CYTOSOL!
RNA Nucleotide
 Phosphate
 Sugar
group
molecule (ribose)
 Nitrogenous
bases
 Adenine – URACIL
 Cytosine - guanine
3 Kinds of RNA
mRNA – (messenger) brings info from
DNA in nucleus to cytosol in eukaryotic
cells (uncoiled)
 tRNA –(transfer) brings amino acids to
mRNA for translation (hairpin shape)
 rRNA –(ribosomal) most abundant, rRNA
makes up the ribosomes where proteins
are made (globular)
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TRANSCRIPTION!!
DNA  RNA

1.RNA polymerase-initiates transcription by
binding to region on DNA called PROMOTER
(causes DNA to separate)-INITIATION PHASE
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2. only ONE of the DNA chains will be used for
transcription it’s called the TEMPLATE
(promoter dictates which of the two strands will
be used)
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3. RNA POLYMERASE – attached to first DNA
nucleotide of template chain – then begins
adding complementary RNA nucleotidesELONGATION PHASE
Cont. Transcription
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4. transcription continues until RNA
polymerase reaches a TERMINATION
SIGNAL on the DNA-TERMINATION
PHASE
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5. RNA polymerase releases both the
DNA mol. And newly formed RNA mol. Are
transcribed in this way (all three!!!)
RNA
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RNA replications
PROKARYOTES
Transcription
and
translation occur in the
SAME place!
NO
NUCLEUS!
Eukaryotes
1. Before RNA leaves the nucleus:
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G (guanine) cap is attached
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A (adenine) tail is attached “many”
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2. These protect the RNA from attack by
cellular enzymes and help ribosomes to
recognize the mRNA (cap & tail are NOT
translated)
Cont. Eukaryotes
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3. INTRONS (non coding sequence) are
removed
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4. EXONS (part of gene that are
expressed) are joined to produce a mRNA
molecule with a continuous coding
sequence.
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NOW RNA CAN LEAVE THE NUCLEUS!
Protein Synthesis
PROTEINS
CARRY OUT
THE GENETIC
INSTRUCTIONS
ENCODED IN AN
ORGANISM’S DNA!!!!
TRANSLATION
The process of assembling from
info. Encoded in a mRNA!
1. mRNA leaves nucleus
 2. mRNA migrates to ribosome in cytosol
for protein synthesis
 3.amino acids floating in cytosol are
transported to ribosomes by tRNA
molecule
 4. peptide bonds join the amino acids to
make polypeptide chain
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Vocabulary!
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1. GENETIC CODE: correlation between a
nucleotide sequence and an amino acid
sequence
2. CODON
3 mRNA nucleotides, codes for
a specific amino acid (64)
3. START CODON (AUG) & a.a. methionine
4. STOP CODON (UAA, UAG, UGA)
5. ANTICODON – 3 tRNA nucleotides carrying
a specific amino acid!
Protein Synthesis
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Protein Synthesis
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Protein Synthesis
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!
THE SUMMARY!
Ribosome
factory for polypeptides
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Two subunits:
Large subunit (top)
 Small subunit (bottom)
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P site – holds tRNA carrying growing polypeptide
A Site – holds tRNA carrying the next amino acid
to be added
Initiation Codon Marks the Start of
an mRNA message
3
PHASES:
1.
INITIATION
2. ELONGATION
3. TERMINATION
INITIATION ( 2 steps)
A) An mRNA mol. Binds to a small
ribosomal subunit. A special initiator
tRNA binds to the specific codon called
the START CODON (UAC binds to start
codon AUG  methionine)
 B) A large ribosomal subunit binds to
the small one creating a functional
ribosome. The initiator tRNA fits into the P
site of the ribosome.
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Elongation and Termination
 Elongation
adds amino acids
to the polypeptide chain until a
stop codon terminates
translation.
3 Steps of Elongation
1. Codon recognition  anticodon of
incoming tRNA carrying amino acid pairs
with mRNA codon in A site.
 2. Peptide bond formation  polypeptide
separates from tRNA (fr. P site). Peptide
bond forms between amino acid in P & A
site  ribosome catalyzes formation of
bond.
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CONTINUE…..
CONTINUE…
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3. Translation  P site tRNA now leaves
ribosome, the ribosome translocates (moves)
the tRNA in the A site, with its attached
polypeptide to the P site. The codon and
anticodon remain bonded and the mRNA and
tRNA move as a unit . This movement brings
into the A site the next mRNA codon to be
translated and process can start again!
ELONGATION CONTINUES UNTIL A STOP
CODON REACHES A SITE.