DNA- The Molecule of Life

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DNA- THE
MOLECULE OF LIFE
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STRUCTURE OF DNA
DNA
(Deoxyribonucleic
Acid): DNA is a long,
stringy, twisted molecule
made up of nucleotides
that carries genetic
information.
DISCOVERIES

Rosalind Franklin, 1952, was studying the
structure of DNA using X-ray diffraction ; helix
1953, JAMES WATSON &
FRANCIS CRICK
 Saw
Franklin’s image and finalized the
structure of DNA
 Called it a “double-helix”
STRUCTURE OF DNA
 Composition: DNA is composed of
nucleotides. The nucleotide is the monomer.

Three parts of a nucleotide:
 1. 5-Carbon Sugar: Deoxyribose
 2. Phosphate Group
 3. Nitrogen Base

DOUBLE HELIX: WHY?
double
helix because it consists
of two long strands of
nucleotides which are twisted
together and when untwisted
resemble a ladder.
 The
sides of the ladder are made of
alternating deoxyribose sugars and
phosphate groups held together by
covalent bonds.

The “rungs” of the ladder are made
up of pairs of nitrogen bases. They
follow the “base-pairing rule”.
BASE PAIRING
NITROGEN BASES
 There
are four different types of
nitrogen bases:
 Purines: Composed of two rings
 1. Adenine (A)
 2. Guanine (G)
 Pyrimidines:
Composed of one ring
3. Cytosine (C)
 4. Thymine (T)
 NOTE: 5. Uracil (U) is found only in
RNA, NOT in DNA

BASE PAIRING RULE:
A
purine always pairs with a
pyrimidine.
 A = T: Held together with two
hydrogen bonds forming a
double bond.
 C = G: Held together with three
hydrogen bonds forming a triple
bond.
BONDS
The
“rungs” of the ladder are
attached to the sugar part of the
side (NOT the phosphate group).
The nitrogen bases are held
together by weak hydrogen
bonds. These weak bonds break
apart easily.

FUNCTIONS OF DNA:
 DNA
codes for proteins and
hormones to be made.
 Proteins result in genetic traits.
 Hormones result in your body
functioning
 The order or sequence of the 4
different nucleotide base pairs and
the number of them determines what
proteins are made and therefore,
what genetic traits are present.
DNA REPLICATION (11/15)
 Definition:
The process of copying
DNA
 Purpose: Gives new cells produced
in mitosis and meiosis a complete set
of chromosomes.
 Where Does DNA Replication
Occur? Nucleus
 When Does DNA Replication
Occur? The S phase of interphase in
the cell cycle
STEPS OF REPLICATION:
 1.
DNA untwists and enzymes break
the hydrogen bonds between the
nitrogen bases. The DNA “unzips”.
 2.
Free-floating nucleotides pair
with each unzipped strand following
the base pairing rule (A with T and
C with G).
·
Each strand of DNA acts a
template.
·
Hydrogen bonds hold the base
pairs together.
 3.
the two new identical molecules of
DNA are twisted back up by
enzymes.
 Link
to animation of process
 DNA replication song: “Backstreet
Boys”
 Result:
Two identical copies of DNA
each composed of one original and
one new strand.
 Why
is replication so important?
 It occurs during interphase so that
each new daughter cell will have a
complete set of chromosomes at the
end of mitosis.
RNA AND TRANSCRIPTION
 RNA:
Ribonucleic Acid
 A nucleic acid molecule that is
similar to DNA but has different
functions.
 Structure: Composed of RNA
nucleotides and is a helix
 link
WHAT IS THE DIFFERENCE?
 RNA
differs from DNA in four
ways:
 1. RNA is single stranded not
doubled.
 2. Has uracil instead of thymine
(still a pyrimidine).
 3. ribose instead of deoxyribose
 4.
There are 3 types of RNA and
only one type of DNA
TYPES OF RNA: 11/17

1. mRNA (messenger): copies instructions in
DNA and carries these to the ribosome. The
message.
TRANSFER RNA
 tRNA
(transfer): carries amino acids
to the ribosome. Contains the anticodon (group of three complementary
nitrogen bases to the codon on
mRNA).
RIBOSOMAL RNA
 rRNA
(ribosomal): makes up the
ribosome. It “reads” the mRNA by
grouping mRNA together into codons
(groups of 3 nitrogen bases.)
PROTEIN SYNTHESIS:
 the
process where information in
DNA is used to build proteins.
 Consists of two processes
transcription and translation.

Transcription: A strand of DNA is
copied into a complementary strand
of mRNA
WHY DOES THIS HAPPEN?
 Why?
DNA cannot leave the nucleus
because it is too big
 needs a “messenger” to carry the
information for making proteins to the
ribosomes.
 mRNA smaller ,single stranded and only a
portion of the DNA is copied so it can
leave the nucleus.
PROCESS:
 1.
DNA is untwisted in only the
parts that contain the information
needing to be copied.
 2. DNA is unzipped by enzymes
 3. Free floating mRNA nucleotides
pair with one of the unzipped
strands of the DNA following the
base pairing rule.
 4.
Note: Uracil replaces thymine.
 5. Only one strand of DNA acts as a
template. The other just “hangs out”
until the process is over.
 6. mRNA breaks from the DNA
template and the mRNA and goes to
a ribosome.
7.
The two strands of DNA zip back
up, reforming the H- bonds
 RESULT:
A single strand of mRNA
is made with information copied
from DNA for the building a specific
protein. link
 Link
to animation
TRANSLATION 11/21
 The
process of converting or
translating information in a
sequence of nitrogen bases in mRNA
into a sequence of amino acids that
make a protein.
 Before translation can begin,
transcription of the DNA into
mRNA must occur.
TRANSLATION :
 mRNA,
3
CONTINUED
rRNA and tRNA are all involved
steps:
 mRNA attaches to the ribosome
(rRNA). (The rRNA slides along the
mRNA like a bead on a string.)
 rRNA “reads” the mRNA in groups of
three nucleotides called a codon.
 (AUG) called the initiator or start codon.




There are three special “stop” codons: UAA, UAG
and UGA. * this is where the protein ends.
Link
Animation link
AMINO ACIDS
 20
different amino acids and 64
different codons. Each amino acid
may have more than one codon but
each codon specifies for only one
amino acid.
MRNA CODON
CHART
MRNA CODON CHART
– LET’S TRY IT!
MUTATIONS 11/23
Def.
Changes in the genetic
material (DNA)
Mutations can occur in two
different types of cells:
1.
Somatic (body) cells
2. Gamete (sex) cells
 Mutations
that occur in somatic
(body) cells usually result in killing
that body cell only.
 Mutations that occur in gamete (sex)
cells means that every cell of the
developing fetus/baby will have that
mutation.
TYPES OF MUTATIONS IN
GAMETE CELLS
2
Types:
1. Gene Mutations
2. Chromosomal Mutations
2
types of Single Gene
Mutations:
a. Point Mutation: a single point
in the DNA sequence is affected.
POINT MUTATIONS (CONTINUED)
 Can
be a substitution in which one
base is changed into another base.
 DNA:
TAC GCA TGG AAT
 mRNA:
AUG CGU ACC UUA
 Amino Acid:Met - Arg - Thr - Leu
 DNA:
TAC GTA TGG AAT
 mRNA:
AUG CAU ACC UUA
 Amino Acid:Met - His - Thr - Leu
2. FRAMESHIFT MUTATION:
a
single gene or nitrogen base is deleted or
added. from the mRNA sequence causing a
shift in the “reading frame” of the genetic
message.
 Can be an insertion
 Can be a deletion
FRAMESHIFT MUTATIONS
 More
dramatic affect.
 may change every amino acid that
follows the point of the mutation
•can alter a protein so much
that it is unable to perform
its normal functions
2ND TYPE OF MUTATION IN GAMETES

5 types of Chromosomal
1. Deletion
 2. Duplication
 3. Inversion
 4. Translocation
 5. Non-disjunction

Mutations:
DO NOT WRITE: JUST LISTEN!
Deletion: Involves the loss of all or part of a
chromosome.
 Duplication: Involves the production of extra
copies of parts of the chromosome.
 Inversion: Reverses the direction of parts of a
chromosome.
 Translocation: When one part of a chromosome
breaks off and attaches to another chromosome.
 Non-disjunction: Means “not coming apart”.
When homologous chromosomes fail to separate
properly during meiosis.

QUEST ON CH. 12 & 13 IS ON :
November 29th = Blue Classes!
November 30th= Gold Classes!
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