Download DNA Deoxyribonucleic Acid

DNA STRUCTURE &
REPLICATION
WHAT IS DNA?


Organic
molecule
Nucleic acid
WHERE IS IT LOCATED?


In the Nucleus
Organized as chromosomes
DNA
STRUCTURE OF DNA



Made of nucleotides
Shaped like a
twisted ladder
“Double helix” =
two twisted strands
DNA STRUCTURE
 Nucleotides
have 3
parts:



Deoxyribose sugar
Phosphate group
Nitrogen base
 Two
types of bases
 Purines
Adenine
 Guanine


Pyrimidines
Thymine
 Cytosine

BASE PAIRING RULES:
cytosine-guanine (C-G)
adenine- thymine (A-T)
LADDER SHAPE (SIDES & RUNGS)
Sides:
 Phosphoric
Acid
 Deoxyribose Sugar
 Phosphoric Acid
Rungs:
 A-T
 T-A
 G-C
 C-G
WATSON & CRICK’S DOUBLE HELIX:
In 1953, James
Watson and Francis
Crick suggested the
model for the
structure of DNA.
This shape is called
a double helix.
WHAT IS DNA’S FUNCTION
?
 Provide
Hereditary
Instructions
 Provides
the
chemical code for
every trait
 Is
a “blueprint” for
making Proteins
DNA REPLICATION
Copying
DNA
 The
number of
chromosomes doubles
 It occurs during
Interphase (S)
 2n to 4n
2N
2N
STEPS FOR DNA REPLICATION:
DNA unzips
1.

Corresponding bases
pair with the existing
DNA strand
2.
DNA reforms
3.

4.
Enzyme = helicase
enzyme = polymerase
2 new strands twist
into helix
Identical
Strands
Where do these
new nucleotides
come from?
The cell
makes them
(from DNA
instructions).
PROTEIN
SYNTHESIS
DNA to Protein
Ch 11.2
14
REVIEW OF DNA REPLICATION
DNA unwinds & unzips (helicase)
 Free nucleotides match with DNA nucleotides & bond
together (polymerase)
 Replicated DNA contains 1 original strand + 1 new
strand.

15
GENES & PROTEINS


Regulate cell functions
 Form cell structures like muscle
filaments, walls of blood vessels, and
transport proteins
 Enzymes control chemical reactions
16
DNA provides the instructions to
make proteins
Different proteins have different
functions:



Proteins are made of amino acids
Sequences of DNA nucleotides
contain information for assembling a
chain of amino acids that make up a
protein.
RNA

1.
2.
3.

Single stranded
Ribose sugar
Bases:
Adenine (A) – Uracil (U)
Guanine (G) – Cytosine (C)
Analogy: In a factory, DNA = instructions for
building a car (proteins) and RNA = the
workers who build it.
17

A nucleic acid like DNA
Different from DNA:
18
TYPES OF RNA

Messenger RNA (mRNA)
Brings information from the DNA in the
nucleus to the cytoplasm
 Found in the nucleus & cytoplasm

Robosomal RNA (rRNA)
Makes up ribosomes, which clamp onto the
mRNA and build protein
 Found only in cytoplasm


Transfer RNA (tRNA)
Transports amino acids to the ribosome to build
a protein
 Found only in cytoplasm

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
TRANSCRIPTION
20
The process of making RNA from DNA:
1.
Enzymes untwist & unzip the DNA
(just like replication)
2.
RNA nucleotides pair with complementary DNA
nucleotides on one of the DNA strands
(Making mRNA)
3.
Once base pairing is complete, mRNA breaks away and
leaves the nucleus
TRANSCRIPTION
A
C
G
U
A
G
C
DNA Code
21
T
mRNA
22
PROCESS OF TRANSCRIPTION
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31
32
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34
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THE GENETIC CODE
(like letters in the English
alphabet)

Proteins are written in the
language of amino acids
(like characters in the Chinese
language)
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Think of the genetic code as a
language:
 DNA and RNA are written in
the language of nucleotides
THE GENETIC CODE



AUG = start
 UAA, UAG, & UGA = stop


The genetic code is universal – all organisms use
the same code.
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
Codon = each set of 3 nucleotides of mRNA that
code for a specific amino acid
64 combinations of nucleotide codons are possible
The order of nucleotides determines the order of
amino acids in a protein
Some codons give instructions
USING A CODON CHART
Examples:
What amino acids are coded for by each of these:
AUG
1.

Methionine
(START)
CCG
2.

Proline (pro)
UAA
3.

STOP
GAC
4.

Aspartic acid
(asp)
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TRANSLATION
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The process of converting the information of mRNA
into a sequence of amino acids
 Takes place in the ribosomes in the cytoplasm
 When mRNA leaves the nucleus and enters the
cytoplasm, ribosomes attach to it like clothespins on a
clothesline.


More than one ribosome at a time
THE IMPORTANCE OF TRNA
In order for proteins to be built, amino
acids need to be carried to the
ribosomes.
 Each tRNA molecule attaches to only
ONE type of amino acid.
 tRNA molecules contain anticodons
that are complementary to mRNA
codons

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tRNA has the
same
nucleotides but
is has a different
shape for its
function
THE PROCESS OF TRANSLATION
1.
2.
○
4.
5.
6.
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3.
A ribosome attaches to mRNA
tRNA molecules carry amino acids to the ribosome and
attach to the mRNA
The ribosome slides down the mRNA to the next codon
The first tRNA leaves the ribosome
A new tRNA molecule carries another amino acid to the
ribosome & enzymes join the two amino acids
The process continues and a chain of amino acids forms
When the ribosome reaches the stop codon, it detaches
from the mRNA and the amino acid chain is released.
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50
We have a
Protein !!!
MUTATIONS
WHAT ARE MUTATIONS?
 Changes
in the
nucleotide sequence of
DNA
 May occur in somatic
cells (aren’t passed to
offspring)
 May occur in gametes
(eggs & sperm) and be
passed to offspring
ARE MUTATIONS HELPFUL OR
HARMFUL?
 Mutations
happen
regularly
 Almost all mutations are
neutral
 Chemicals & UV radiation
cause mutations
 Many mutations are
repaired by enzymes
ARE MUTATIONS HELPFUL OR
HARMFUL?
Some
types of skin
cancers result from
somatic mutations
Some mutations may
improve an organism’s
survival (beneficial)
TYPES OF
MUTATIONS
CHROMOSOME
MUTATIONS
Five
types exist:
 Deletion
 Inversion
 Translocation
 Nondisjunction
 Duplication
CHROMOSOME MUTATIONS
 May
Involve:
 Changing the
structure of a
chromosome
 The loss or
gain of part of
a chromosome
DELETION
Due
to breakage
A piece of a
chromosome is lost
INVERSION
Chromosome
segment
breaks off
Segment flips around
backwards
Segment reattaches
DUPLICATION
Occurs
when a
gene sequence is
repeated
TRANSLOCATION
Involves
two
chromosomes that
aren’t homologous
Part of one
chromosome is
transferred to
another
chromosomes
TRANSLOCATION
NONDISJUNCTION
Failure
of chromosomes to
separate during meiosis
Causes gamete to have too many
or too few chromosomes
Disorders:
CHROMOSOME MUTATIONS

Down Syndrome



Chromosome 21 does
not separate correctly.
They have 47
chromosomes in stead
of 46.
Children with Down
Syndrome develop
slower, may have heart
and stomach illnesses
and vary greatly in
their degree of
inteligence.
CHROMOSOME MUTATIONS

Cri-du-chat
Deletion of material on 5th
chromosome
 Characterized by the cat-like cry
made by cri-du-chat babies
 Varied levels of mental handicaps

SEX CHROMOSOME ABNORMALITIES
 Klinefelter’s
Syndrome
XXY, XXYY, XXXY
 Male
 Sterility
 Small testicles
 Breast enlargement

SEX CHROMOSOME ABNORMALITIES
 XYY



Syndrome
Normal male traits
Often tall and thin
Associated with antisocial and behavioral
problems
SEX CHROMOSOME MUTATIONS
 Turner’s
Syndrome
X
 Female
 sex organs don't
mature at
adolescence
 sterility
 short stature

SEX CHROMOSOME MUTATIONS

XXX






Trisomy X
Female
Little or no visible differences
tall stature
learning disabilities
limited fertility
CHROMOSOME MUTATION
ANIMATION
GENE MUTATIONS
Change
in the
nucleotide
sequence of a gene
May only involve a
single nucleotide
May be due to
copying errors,
chemicals, viruses,
etc.
TYPES OF GENE MUTATIONS
Include:
 Point Mutations
 Substitutions
 Insertions
 Deletions
 Frameshift
POINT MUTATION
Change
of a single
nucleotide
Includes the deletion,
insertion, or
substitution of ONE
nucleotide in a gene
POINT MUTATION
Sickle
Cell
disease is the
result of one
nucleotide
substitution
Occurs in the
hemoglobin
gene
FRAMESHIFT MUTATION
Inserting
or deleting
one or more
nucleotides
Changes the “reading
frame” like changing a
sentence
Proteins built
incorrectly
FRAMESHIFT MUTATION
Original:
 The
fat cat ate the wee
rat.
Frame Shift (“a” added):
 The fat caa tet hew
eer at.
AMINO ACID SEQUENCE
CHANGED
GENE MUTATION
ANIMATION
REVIEW QUESTIONS
1.
2.
3.
4.
5.
Where can mutations take place?
What are the five types of mutations?
What is nondisjunction?
Name and summarize a genetic disorder.
Explain how mutations are harmful and
beneficial to humans.