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Honors
Biology
Ch. 12
Molecular Genetics
CH. 11 Molecular Genetics
I. DNA: The Chemical
Basis of Heredity
- forms the universal
genetic code of cells
- contains instructions
for making all of a
cell’s proteins
James Watson & Francis Crick
- discovered the structure of DNA in 1953
X-ray Diffraction of DNA
A.DNA Structure
1. Components of DNA
(3 Main Parts)
a. Sugar
(Deoxyribose)
b. Phosphate
c. Bases
c. Bases
1) Adenine (A)
Guanine (G)
2) Cytosine (C)
Thymine (T)
2. Nucleotide:
- a subunit of
a nucleic acid
containing
a sugar,
a phosphate,
and a base
3. DNA Shape:
- double helix
a. backbone - sugars
and phosphates
b. paired bases form
on the inside
c. Base Pairing Rule:
A:T, C:G
The Watson-Crick Model
of DNA Structure
B.Replication:
- process by which DNA makes an
exact copy of itself
Free
Nucleotides
DNA
Replication
New
double
helix with
1 old &
1 new
strand
Parental
DNA
double
helix
II. From DNA to Protein
A. Genes and Protein
1.Gene
- a specific sequence of
bases in DNA that
determines the sequence
of amino acids in a protein
2. Proteins
- very complex structure
- 3 basic shapes: helix, pleated
sheet, globular
- proteins contain between 50 2000 amino acids
Illustration of Protein Structure
Primary
(Amino Acid
Sequence)
Tertiary
(Bending)
Quaternary
(Layering)
Secondary
(Helix)
Pleated Sheets
Hydrogen
Bonds
Structural Proteins
Horn
Hair
Spiderweb
Hair
Structure
Hair
Cell
Single hair
Microfibril
Protofibril
|
S
|
Hydrogen bonds
S
|
|
S
|
S
|
disulfide
bridges
Curling of Hair
S
|
|
|
S
|
|
S
S
|
|
|
S
|
S
S
|
|
|
S
|
Permanent
Wave
S
|
Naturally
Curly
Hair
|
S
|
S
|
|
S
Straight
Hair
B. RNA Structure:
- Nucleic acid
that makes
protein
B.RNA Structure:
Shape
Sugar
Base
Size
Location
Function
DNA
double helix
deoxyribose
thymine
very large
nucleus
- stores genetic
info
- replication
- makes RNA
RNA
single helix
ribose
uracil
smaller
cytoplasm
- makes
protein
C.Transcription:
- the copying
of a genetic
message
from DNA
to RNA
Original DNA
C.Transcription:
- the copying
of a genetic
message
from DNA
to RNA
DNA base
pairs separate
C.Transcription:
- the copying
of a genetic
message
from DNA
to RNA
DNA half
‘transcribes’ RNA
C.Transcription:
- the copying
of a genetic
message
from DNA
to RNA
RNA released to
make protein
Transcription: First Two Steps
Transcription: Last Step
Information Flow:
DNA
RNA
Protein
RNA Transcription in Action
Three Types of RNA
mRNA
A G A U G C G A G U U A U G G
codons
Ribosome
contains rRNA
Met Amino
acid
tRNA
anticodon
Large
subunit
1 2
Small
subunit
tRNA
docking
sites
UGA
D.Messenger RNA (mRNA):
- carries the information for
making a protein from DNA
to the ribosomes
- acts as a template (pattern)
- contains codons:
triplets of bases that code
for a particular amino acid
- Start Codon:
(AUG) - marks the start of a
polypeptide
- Stop Codon:
(UAA, UAG, UGA) - marks
the end
E. Transfer RNA (tRNA):
- carries amino acid to specific
place on mRNA
- contains Anticodon:
triplet of bases complimentary
to mRNA codon
F. Ribosomal RNA (rRNA):
- transcribed in nucleus and
combined with protein into
ribosomes (site of protein
synthesis)
III.Translation:
- protein synthesis
- decoding the "message" of
mRNA into a protein
Information Flow:
DNA
RNA
Protein
Translation: Initiation
Translation: Elongation 1
Translation: Elongation 2
Translation: Elongation 3
Translation: Elongation 4
Translation: Elongation 5
Translation: Termination
IV. Genetic Mutations
IV. Genetic Mutations
- any change in the nucleotide
sequence of DNA
- can occur in any cell
* Somatic Mutations:
- may be harmful but not inherited
* Gamete Mutations:
- can be inherited
IV. Genetic Mutations
-
usually recessive
most are harmful
some harmless
few beneficial
(leads to evolution)
A. Causes:
- Mutagens:
- UV, X-rays, other
radiation, chemicals
(asbestos, etc.)
B. Types of Mutations:
1. Point Mutation
- change of a single base
- ex: sickle-cell anemia
AUG GGG CUU CUU AAU
AUG GGG CAU CUU AAU
Normal Red Blood Cells
Sickled Cells
2. Frameshift Mutation
- addition or deletion of a
single base
AUG GGG CUU CUU AAU
AUG GGG CAU UCU UAA U
3. Chromosomal Mutation
- change in an entire chromosome
or in chromosome number within
a cell
a) Translocation:
- transfer of a chromosome
segment to a nonhomologous
chromosome
Normal
Translocation
b) Inversion:
- rotation of a chromosome
segment
Normal
Inversion
c) Insertion:
- breaking off of a chromosome
segment and attaching to its
homologue
Normal
Insertion
d) Deletion :
- chromosome segment left out
Normal
Deletion
e) Nondisjunction :
- failure of homologous
chromosomes to segregate
during meiosis
Human Chromosomes
(23 homologous pairs)
Down syndrome
(Trisomy 21)
Number per 1000 Births
Incidence of Down Syndrome
400
300
200
100
0
10
20
30
40
Age of Mother (years)
50
Klinefelter’s syndrome
(XXY)
f) Polyploidy :
- having a multiple set(s) of
chromosomes
Speciation by Autopolyploidy
in Plants
Failure of cell division
in a cell of a growing
diploid plant after
chromosome duplication
gives rise to a tetraploid
branch or other tissue.
Gametes produced
by flowers on this
branch will be diploid.
Offspring with tetraploid
karyotypes may be viable
and fertile—a new
biological species.
2n
2n = 6
4n = 12
4n
The Evolution of
Wheat
A Tetraploid Mammal
Turner’s Syndrome (Monosomy X)
XYY Syndrome
Trisomy X (XXX)
Klinefelter’s Syndrome (XXY)
Down Syndrome (Trisomy 21)
Normal Female
Edward’s Syndrome (Trisomy 18)
Cri du Chat (deletion in chromosome 5)
The
End
of Ch. 11
(Cytoplasm)
DNA
(Nucleus)
rRNA mRNA
+ Proteins
Overview
of
1 Transcription
Information Flow
tRNA
tRNA
Ribosomes
mRNA
tRNA-AA
2 Translation
Inactive
Protein
Active
Protein
3 Modification
4 Degradation
Substrate
Product
Amino
Acids
Complementary Base Pairing
gene
(a) complementary
DNA strand
G
C
A
T
G
G
G
A
G
T
T
template
DNA strand
C
G
T
A
C
C
C
T
C
A
A
G
U
U
codons
(b) mRNA
G
C
A
U
G
G
G
A
anticodons
(c) tRNA
U
A
C
C
C
U
C
A
A
amino acids
(d) protein
Methionine
Glycine
Valine