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DNA AND PROTEIN
SYNTHESIS
DNA (DEOXYRIBONUCLEIC ACID)
• Nucleic acid that is found in
chromosomes and carries genetic
information.
Watson and Crick
• Chargaff
• Rosalind Franklin & Maurice Wilkins
(crystalline x-ray diffraction patterns)
CHROMOSOME ORGANIZATION
1. A chromosome is an enormous strand of
super coiled DNA.
2. Sections of DNA on the chromosome that
code for proteins are called genes.
3. Noncoding sections of DNA are called
“junk DNA”
http://www.allaboutscience.org/junk-dna.htm
BUILDING BLOCKS OF DNA
Composed of nucleotides
• Nucleotides contain three parts:
1. 5-Carbon Sugar (deoxyribose)
2. Phosphate Group
3. Nitrogen Base (four types, adenine,
guanine, thymine and cytosine)
• Adenine and Guanine are purines
(composed of two rings of nitrogen atoms)
• Thymine and Cytosine are pyrimidines
(composed of one ring of nitrogen atoms)
STRUCTURE OF DNA
• Consists of two strands of nucleotides that
form a twisted ladder (double helix)
• Sugar and phosphate alternate along the
sides of the ladder (linked by strong
covalent bonds)
• Pairs of nitrogen bases form the rungs of
the ladder (linked by weak hydrogen
bonds).
• Specific base pairing arrangement
(Chargaff’s Rule)
A-T : 2 hydrogen bonds
C-G : 3 hydrogen bonds
• Nitrogen bases attach to the sugar portion
of the side (NOT the phosphate)
• Strands run in opposite directions
FUNCTION OF DNA
• DNA codes for proteins (structural
proteins, enzymes, and hormones)
• information for building proteins is carried
in the sequence of nitrogen bases
• proteins determine physical and metabolic
traits and regulate growth and
development.
Packaged
• DNA and protein is packed together to
form chromatin.
• Chromatin is DNA that is coiled around
circular proteins called histones.
DNA REPLICATION
Process in which DNA is copied
PURPOSE OF DNA REPLICATION
Gives daughter cells produced by cell
division a complete set of genetic
information identical to the parent cell.
WHERE REPLICATION OCCURS
Nucleus
WHEN DURING THE CELL CYCLE
REPLICATION OCCURS
Interphase (S)
HOW REPLICATION OCCURS
1. Helicase enzymes unzip the parent
strand by separating the nitrogen base
pairs.
2. DNA polymerase pairs free DNA
nucleotides with the exposed bases on
both strands following the base pair rules.
• each strand from the parent molecule
serve as a template
3. Hydrogen bonds reform spontaneously
sealing the two strands of each DNA
molecule together.
DNA polymerase also proofreads each new
DNA strand to make sure there are no
mistakes.
RESULTS OF REPLICATION
• Two molecules of DNA that are identical
• Each is half old (strand from parent) and
half new (strand synthesized by DNA
polymerase)
RNA (RIBONUCLEIC ACID)
Nucleic acid involved in the synthesis
of proteins
RNA STRUCTURE
Composed of nucleotides, but differs from
DNA in three ways.
1. Single strand of nucleotides instead of
double stranded
2. Has uracil instead of thymine
3. Contains ribose instead of deoxyribose
RNA FUNCTION
Three forms of RNA involved in protein
synthesis
1. mRNA (messenger): copies instructions
in DNA and carries these to the
ribosome.
2. tRNA (transfer): carries amino acids to
the ribosome.
3. rRNA (ribosomal): composes the
ribosome.
PROTEIN SYNTHESIS
Cells build proteins following instructions
coded in genes (DNA).
• Consists of two parts, transcription and
translation
TRANSCRIPTION
DNA is copied into a complementary strand
of mRNA.
WHY?
• DNA cannot leave the nucleus. Proteins
are made in the cytoplasm. mRNA serves
as a “messenger” and carries the protein
building instructions to the ribosomes in
the cytoplasm.
LOCATION OF TRANSCRIPTION
Nucleus
HOW TRANSCRIPTION OCCURS
1. RNA polymerase untwists and unzips a
section of DNA (usually a single gene)
from a chromosome.
2. RNA polymerase pairs free RNA
nucleotides to the exposed bases of one
of the DNA strands following base pair
rules.
• Uracil replaces thymine
• Only 1 strand of DNA serves as a
template, the other “hangs out”
3. Newly synthesized mRNA separates
from template DNA and DNA zips back up.
RESULT OF TRANSCRIPTION
mRNA strand with instructions for building a
protein that leaves the nucleus and goes
to the cytoplasm.
TRANSCRIPTION EXAMPLE
• Transcribe the following DNA Sequence in
mRNA pg. 303
TAC CGG ATC CTA GGA TCA
AUG GCC UAG GAU CCU AGU
PROTEINS
Structural and functional components of
organisms.
• Composed of amino acids
• order of nucleotides in DNA determines
order of amino acids in a protein
• One gene codes for one protein
GENETIC CODE
The “language” that translates the sequence
of nitrogen bases in DNA (mRNA) into the
amino acids of a protein.
• Codon = three nucleotides on DNA or
mRNA
• One codon specifies one amino acid
• Some codons are redundant (code for the
same amino acid)
• The genetic code is universal to all
organisms
DNA: TAC CTT GTG CAT GGG ATC
mRNA AUG GAA CAC GUA CCC UAG
A.A
MET G.A HIS VAL PRO STOP
IMPORTANT CODONS
• AUG = start translation (Met)
• UAA, UAG, UGA= stop translation
TRANSLATION
Instructions in mRNA are used to build a
protein
LOCATION OF TRANSLATION
ribosome (in the cytoplasm)
PROCESS OF TRANSLATION
1. mRNA binds to the ribosome.
2. Ribosome searches for start codon
(AUG)
3. tRNA brings correct amino acid
(methionine) to the ribosome.
• Each tRNA carries one type of amino acid.
• The anticodon (three nitrogen bases on
tRNA) must complement codon for amino
acid to be added to protein chain
4. ribosome reads next codon
5. tRNA’s continue lining up amino acids
according to codons
6. peptide bonds link amino acids together
7. ribosome reaches STOP codon
• Amino acid chain is released
http://www.pbs.org/wgbh/aso/tryit/dna/shock
wave.html
RESULT OF TRANSLATION
A Protein
http://www.courses.fas.harvard.edu/~biotext/
animations/TRANSLATE20b.swf
http://highered.mcgrawhill.com/sites/0072437316/student_view0/
chapter15/animations.html#
End of sec. 1-3
Chapter 12
Electrophoresis
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Technique for molecular separation.
Molecules are separated in a gel.
The gel is placed in an electrical field.
Like charges repel, unlike charges attract.
What is DNA Profiling?
A technique used by scientists to
distinguish between individuals of the
same species using only samples of their
DNA
Who Invented it?
• The process of DNA
fingerprinting was
invented by Alec
Jeffreys at the
University of Leicester
in 1985.
• He was knighted in
1994.
Stages of DNA Profiling
• Stage 1:
Cells are broken down
to release DNA
If only a small amount of
DNA is available it can be
amplified using the
polymerase chain
reaction (PCR)
Stages of DNA Profiling
• Step 2:
The DNA is cut into fragments using restriction enzymes.
Each restriction enzyme cuts DNA at a specific base
sequence.
Stages of DNA Profiling
• The sections of DNA that are cut out are
called restriction fragments.
• This yields thousands of restriction
fragments of all different sizes because
the base sequences being cut may be far
apart (long fragment) or close together
(short fragment).
Stages of DNA Profiling
Stage 3:
• Fragments are
separated on the
basis of size using a
process called gel
electrophoresis.
• DNA fragments are
injected into wells and
an electric current is
applied along the gel.
Stages of DNA Profiling
DNA is negatively
charged so it is
attracted to the
positive end of the
gel.
The shorter DNA
fragments move
faster than the longer
fragments.
DNA is separated on
basis of size.
Stages of DNA Profiling
• A radioactive material
is added which
combines with the
DNA fragments to
produce a fluorescent
image.
• A photographic copy
of the DNA bands is
obtained.
Stages of DNA Profiling
Stage 4:
• The pattern of fragment distribution is then
analysed.
Uses of DNA Profiling
• DNA profiling is
used to solve
crimes and
medical problems
Crime
• Forensic science is the use of scientific
knowledge in legal situations.
• The DNA profile of each individual is
highly specific.
• The chances of two people having exactly
the same DNA profile is 30,000 million to 1
(except for identical twins).
Biological materials used for DNA
profiling
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Blood
Hair
Saliva
Semen
Body tissue cells
DNA samples have been
obtained from vaginal
cells transferred to the
outside of a condom
during sexual intercourse.
DNA Profiling can solve crimes
• The pattern of the DNA profile is then compared
with those of the victim and the suspect.
• If the profile matches the suspect it provides
strong evidence that the suspect was present at
the crime scene (NB:it does not prove they
committed the crime).
• If the profile doesn’t match the suspect then that
suspect may be eliminated from the enquiry.
Example
• A violent murder occurred.
• The forensics team retrieved a blood
sample from the crime scene.
• They prepared DNA profiles of the blood
sample, the victim and a suspect as
follows:
Was the suspect at the crime
scene?
Suspects
Profile
Blood sample from
crime scene
Victims
profile
Solving Medical Problems
DNA profiles can be used to determine whether a
particular person is the parent of a child.
A childs paternity (father) and maternity(mother)
can be determined.
This information can be used in
• Paternity suits
• Inheritance cases
• Immigration cases
Example: A Paternity Test
• By comparing the DNA profile of a
mother and her child it is possible to
identify DNA fragments in the child
which are absent from the mother and
must therefore have been inherited
from the biological father.
Is this man the father of the child?
Mother
Child
Man
Famous Cases
• Colin Pitchfork was
the first criminal
caught based on DNA
fingerprinting
evidence.
• He was arrested in
1986 for the rape and
murder of two girls
and was sentenced in
1988.
• Electrophoresis Virtual Lab