Download DNA and Genes

DNA Structure
1
DNA
I DNA is often called the
blueprint of life.
I In simple terms, DNA
contains the
instructions for making
proteins within the cell.
I DNA is universal.
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DNA… codes for proteins
Proteins are important:
• Your skin, muscles &
bones are made of
protein
• All chemical reactions
needed for life (such as
eating, running, thinking,
etc) depends on
enzymes which are
proteins.
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Watson & Crick’s Model
Watson and Crick first
discovered the double
helix structure of DNA in
1953.
They walked into the
office of a scientific
publication and
announced, “We have
found the secret of life”.
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Why do we study DNA?
DNA
Its central importance to all
life on Earth
I Medical benefits such as
cures for diseases and
understanding cancer and
birth defects
I Better food crops- genetic
engineering
I CSI – criminal investigations
I
Chromosomes and DNA
Where is DNA found?
I DNA is the material the makes up our genes
which code for certain traits and proteins.
I Our genes are on our chromosomes.
I Simply…Chromosomes are made up of a
chemical called DNA.
DNA – The Double Helix Molecule
I DNA is a very long
polymer.
I The basic shape is
like a twisted ladder
or zipper.
I The DNA double
helix has two
strands twisted
together.
One Strand of DNA
phosphate
I The backbone of the
molecule is alternating
Phosphate
deoxyribose
I and
Deoxyribose sugar
I The teeth are
Nitrogenous bases
bases
One Strand of DNA
IOne strand of DNA
is a polymer of
nucleotides.
IOne strand of DNA
has many
millions of
nucleotides.
nucleotide
Nucleotides
One deoxyribose together with its
phosphate and base make a nucleotide.
O
O -P O
O
C
C
C
Phosphate
O
C
C
O Deoxyribose
Nitrogenous
base
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Four Nitrogenous Bases
DNA has four different bases:
I
Cytosine C
T
I Adenine A
I Guanine G
I Thymine
Two Kinds of Bases in DNA
IPyrimidines are
single ring bases.
IPurines are double
ring bases.
N
N C
O C
C
N C
N
N C
C
C
N
N C
N C
Purines:
Adenine & Guanine
I
Adenine and guanine each have two rings of
carbon and nitrogen atoms.
I All Grandmas are Pure (purines)
N
C
Adenine
N
C
C
N
O
N
C
N
N
C
N
C
C
C
N
Guanine
C
N
N
C
Pyrminidines:
Thymine & Cytosine
I Thymine and cytosine each have one ring
of carbon and nitrogen atoms.
I King Tut and Cleopatra lived in Pyramids
(pyrimidines)
N
O
C
C
O
C C
N
C
Thymine
N
O
C
C
N
C
N
C
Cytosine
Two Stranded DNA
I Remember, DNA has
two strands that fit
together something
like a zipper.
I The teeth are the
nitrogenous bases
but why do they
stick together?
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I
N
N
C
C
guanine
C
C
N
cytosine
C
C
N
N
N
C
I
The bases attract each
other because of
hydrogen bonds.
Hydrogen bonds are weak
but there are millions and
millions of them in a
single molecule of DNA.
The bonds between
cytosine and guanine are
shown here with dotted
lines
O
I
C
N
Hydrogen Bonds
N
C
O
Hydrogen Bonds, cont.
When making
hydrogen bonds,
cytosine always
pairs up with
guanine
I Adenine always pairs
up with thymine
I Adenine is bonded to
thymine here
I
N
N
N
C
adenine
C
N
O C
thymine
N
C
C
N
N
C
O
C
C
C C
Chargraff’s Rule:
I Adenine and Thymine always
join together
A
T
I Cytosine and Guanine always
join together
C
G
DNA by the Numbers
Each cell has about
2m of DNA.
I The average human
has 75 trillion cells.
I The average human
has enough DNA to go
from the earth to the
sun more than 400
times.
I DNA has a diameter of
only 0.000000002 m.
I
The earth is 150 billion m
or 93 million miles from
the sun.
DNA Replication
DNA Replication
I DNA replication produces two
molecules from one
I Each strand serves as a pattern to
make a new DNA molecule.
I Begins as an enzyme that breaks the
hydrogen bonds between the nitrogen
bases and unzips the strand.
Replication Continued
I Nucleotides that are floating free in the
nucleus bond to the single stands by base
pairing.
I Another enzyme bonds these new
nucleotides into a chain.
I Each new strand formed is a complement of
one of the original
I DNA Replication Animation
DNA Replication
Let’s Practice:
Write the complimentary strand for DNA…
TGACCGAT
ACTGGCTA
TGGCCAATATA
ACCGGTTATAT
Protein Synthesis
I Proteins form key cell structures and
regulate cell functions (enzymes)
I The protein’s “code” is supplied by the
DNA in the nucleus.
I But proteins are “manufactured” in the
ribosomes in the cytoplasm.
I So how does protein synthesis occur?
Protein Synthesis
I Step 1: Transcription (to re-write)
• DNA is too large to go from the nucleus to the
cytoplasm, so only pieces of DNA are copied
into RNA. This RNA then travels from the
nucleus to the cytoplasm.
I Step 2: Translation (to make useful)
• The RNA is then made into something useful,
like assembling amino acids into proteins in
the ribosome
RNA
I RNA is a single strand
I The simple sugar in RNA is
ribose
I Nitrogen bases in RNA:
• Adenine
• Guanine
• Cytosine
• Uracil (replaces thymine bonds with adenine)
Types of RNA
I Messenger RNA (mRNA) = brings
information from the DNA in the nucleus to
the cell’s cytoplasm
I Ribosomal RNA (rRNA) = part of the
ribosome that clamps onto the mRNA and
helps to assemble the amino acids in the
correct order.
I Transfer RNA (tRNA) = transports amino
acids to the ribosome to be assembled
into a protein.
Protein Synthesis - Transcription
I Similar to DNA replication, but the result is
the formation of one single-stranded RNA
molecule (mRNA)
I Process:
• Enzyme unzips the DNA molecule
• Free RNA nucleotides pair with complementary
DNA nucleotides
• When pairing is complete, mRNA molecule breaks
away. The DNA rejoins the original strand. The
mRNA leaves the nucleus and enters the
cytoplasm to join with the ribosome.
Protein Synthesis - Transcription
Let’s Practice:
Write the complimentary strand for mRNA…
TGACCGAT
ACUGGCUA
TGGCCAATATA
ACCGGUUAUAU
Protein Synthesis
Protein Synthesis - Translation
1. Once the newly made
mRNA leaves the
nucleus, it attaches to
the ribosome.
2. Ribosomes will “read” 3
nucleotides called
codons in the mRNA
code at a time.
• Each codon codes for:
– an amino acid
– a START signal ( AUG )
– a STOP signal ( UAA, UAG, and
UGA )
Codon
Protein Synthesis - Translation
3. When the ribosome
reads the start
sequence ( AUG ), a
tRNA molecule comes
along with the
anticodon ( UAC ) and
the amino acid ( MET ).
• The anticodon is the
complementary
sequence.
anticodon
Protein Synthesis - Translation
4. The ribosome
then reads the
next codons on
the mRNA and
tRNA transfers
the amino
acids to build
the protein
until a “stop”
codon is read.
Codon Chart for mRNA
Let’s Break the Genetic Code
1. Start with DNA:
TACTAGCTAACC
2. Write the complimentary strand for mRNA
AUGAUCGAUUGG
3. Identify the codons on the mRNA
AUG-AUC-GAU-UGG
4. Identify the anticodons on the tRNA
UAC-UAG-CUA-ACC
5. Identify the amino acid sequence from the mRNA
Met - Iso - Asp - stop
Genetic Mutations
I Any change in the DNA sequence is called a
mutation.
• Mutations can effect reproductive cells
– Will be passed on to offspring
• Mutations can effect body cells
– Example = CANCER
Genetic Mutations
Everyone acquires some changes to their DNA
during the course of their lives.
I These changes occur in a number of ways.
Sometimes there are simple copying errors that
are introduced when DNA replicates itself. (Every
time a cell divides, all of its DNA is duplicated so
that the each of the two resulting cells have a full
set of DNA.)
I Other changes are introduced as a result of DNA
damage through environmental agents including
sunlight, cigarette smoke, and radiation.
I
Genetic Mutations
I
I
I
Our cells have built in mechanisms that catch and repair
most of the changes that occur during DNA replication or from
environmental damage.
Some of these changes occur in cells of the body — such as
in skin cells as a result of sun exposure — but are not passed
on to children.
But other errors can occur in the DNA of cells that produce the
eggs and sperm.
• These are called germline mutations and can be passed from parent
to child.
• If a child inherits a germline mutation from their parents, every cell in
their body will have this error in their DNA.
• Germline mutations are what cause diseases to run in families
Genetic Mutations
I Types of DNA Mutations:
• Point mutation
• Frameshift mutation
• Inversion
Not All Mutations are BAD!
I Some result in characteristics that give the
organism a greater chance of survival.
I Example: Sickle cell anemia (deflated look
of red blood cells) is caused by a mutation,
however it is beneficial to people in Africa
who often contract malaria – the parasite
can no longer attach to their red blood
cells, therefore they aren't affected
Point Mutation
I A change in a single base pair in DNA
I Example:
• THE DOG BIT THE CAT.
• THE DOG BIT THE CAR.
I Can change the entire structure of a
protein, and effect the shape of the protein.
Frameshift Mutation
A single base pair in DNA is deleted or added.
I Every codon after the deleted base would be
different.
I This type of mutation can make the DNA
meaningless and often results in a shortened
protein.
I Example:
I
• THE DOG BIT THE CAT.
• THE DOB ITT HEC AT.
Inversion
In an inversion mutation, an entire section of DNA
is reversed.
I A small inversion may involve only a few bases
within a gene, while longer inversions involve
large regions of a chromosome containing
several genes.
I
Original: The fat cat ate the wee rat.
I Inversion: The fat tar eew eht eta tac.
I
Causes of Mutations
I Spontaneous:
• Mistake in base pairing during DNA replication
I Mutagen – agent that causes DNA change
• High energy radiation
– X rays
• Chemicals
– Dioxins, asbestos, benzene, cyanide, formaldehyde
• High temperatures
Mutation Video
4 Types of Chromosomal Mutations
• Deletions occur when part of a chromosome is left
out. video
• Insertions occur when a part of a chromatid
breaks off and attaches to its sister chromatid.
• Inversion occur when part of a chromosome
breaks off and is reinserted backwards.
• Translocation occur when part of one
chromosome breaks off and is added to a different
chromosome video