Download DNA

Take out a blank sheet of paper
On the paper write :
1. your name (first and last)
2. The date today 5/7)
3. The letter of the correct answer to the following question
1. A parent homozygous for Type B blood
marries a person with Type AB blood. What is
the probability they will have a child with type
A blood?
A. 0%
C. 50%
B. 25%.
D. 100%.
Multiple Alleles
Often each allele has its own effect and the
alleles are considered codominant.
Human ABO Blood type
Type
Type
Type
Type
A individuals only galactosamine
B individuals add only galactose
AB individuals add both sugars
O individuals add neither sugar
Rh Blood Group
Rh cell surface marker
Epistasis
Epistasis - Interaction between products of
two genes where one gene modifies the
other gene’s phenotypic expression.
Emerson - To produce pigment, a Zea mays
plant must possess at least one functional copy
of each enzyme gene.
Epistasis
Sex Linkage

A trait determined by a gene on the sex
chromosome is said to be sex-linked.
– In Drosophila, sex is determined by the number
of copies of the x chromosome.
Eye color gene is carried on
the X chromosome
What alleles will the
sperm have?
What alleles will the
eggs have?
XR
XR
Y
X RX R
X RY
Xr
X RX r
X rY
Heterozygous for
red eye color
Offspring
phenotypes
All females
have red eyes
½ of the males
have white
eyes and ½ the
males have
red eyes
Mutations in Human
Heredity
Mutations are accidental changes in genes.
– Rare, random, and usually result in recessive
alleles.
Pedigrees used to study heredity.
– Hemophilia - Inherited condition where blood is
slow to clot or does not clot at all.
 Only expressed when individual has no copies of the
normal allele.
 Royal Hempohilia - Sex-linked
Sickle-Cell Anemia

Sickle-Cell Anemia is a recessive
inherited disorder in which afflicted
individuals have defective hemoglobin,
and thus are unable to properly
transport oxygen to tissues.
Heterozygotes usually appear normal.
 Homozygotes have Sickle-Cell, but are
resistant to malaria.

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Other Disorders

Tay-Sachs
– Incurable heredity disorder which causes brain
to deteriorates.


Nonfunctional form of hexosaminidas A enzyme.
Huntington’s Disease
– Inherited condition caused by dominant allele
causing progressive brain deterioration.

Symptoms usually develop late in life.
Genetic Counseling and
Therapy

Process of identifying parents at risk of
producing children with genetic
defects and assessing genetic state of
early embryos.
– Amniocentesis
– Ultrasound
– Chorionic Villi Sampling
Pedigree Analysis
 Mendel’s laws allow us to analyze the genetic information
in family records (pedigrees)
 From this we can determine the nature of alleles that
control traits. From this we can:
deduce whether the trait is dominant or recessive
deduce whether the trait is sex linked
deduce the genotypes of members of the family
predict the phenotypes of future offspring
deduce the genotypes of parents from their offspring
phenotypes


In a pedigree, each
individual is represented
by a symbol
The shape, color, and
location of the symbol
carry information about
the sex and phenotype
of the individual

A dominant allele has a different pattern of
inheritance:
Aa
Aa
Trait A
dominant
Only a a for recessive trait
expression so both
parents have to have a
recessive allele
Enzymes serve as a catalyst for chemical reactions by
lowering the activation energy.
Enzymes also function to control the rate of a reaction.
Products: less energy content
Products: more energy content
The laws of thermodynamics dictate that a reaction will not
proceed spontaneously unless the molecules that result from the
reaction, the products, have lower energy than the molecules
that began the reaction, the reactants.
An Energy Diagram of a Reaction:
a Plot of State Versus Energy
A plot of the free energy of the reaction vs
the course of the reaction:
A reaction is a change
A~B
C~D of state of matter
Original energy state
of the reactants
Energy
Final energy state of the
products (exergonic)
A-B
C-D
EA activation energy
DG
A-C
B-D
Course of the reaction
Spontaneous: Clarification
Spontaneous reactions do NOT just go forward
immediately to produce products.
This is because the reactants must overcome an
activation energy, EA.
Enzymes
Enzymes are protein catalysts that
enormously speed up reactions. They often
have an “-ase” ending to their name.
e.g., hexokinase, catalase, peptidase, mutase
They are not themselves changed (except for
a brief period of time) and are the same
before and after a reaction.
Enzymes:
1. Lower the activation energy: this is the MOST
important characteristic
2. Do not add or remove energy from a reaction
3. Do not change the equilibrium for a reaction
4. Are reused over and over
Enzyme Function
DNA – the heredity material

Very early it was discovered
chromosomes are composed of
proteins and DNA. But it took several
experiments to conclusively determine
specifically which substance made up
genes.
Griffith Experiment
Documented movement of genes from
one organism to another
(transformation 1928).
– Avery Experiment (1944)
 Removed
almost all protein from
bacteria, and found no reduction in
transforming activity.
– Hershey-Chase (1952)
 Used
radioactive isotopes to label DNA
and protein. Found genes used to
specify new generations of viruses
were made of DNA.
DNA - genetic material

Eukaryotes
– DNA located in the
nucleus
membrane bound
organelle

Prokaryotes
– DNA located in the
nucleoid. No membrane
surrounded organelle
Discovering DNA Structure

DNA made up of nucleotides.
– Central sugar, phosphate group, and an
organic base.

Purines - Large bases
– Adenine and Guanine

Pyrimidines - Small bases
– Cytosine and Thymine
Nucleotide Base
DNA – 4 nucleotide bases
4 base nucleotides
Chargaff’s Rule
A =T and G=C
Discovering DNA Structure
Watson
and Crick
1953
&( Wilkins)
deduced
structure
of DNA
as a
double
helix.

Base pairs
linked
5‘
end
3‘
end
3‘
end
5‘
end
Double Helix structure



two stands of
nucleotides
Outer part of the
ladder is the sugarphosphate backbone
Anti-parallel allows
for H-bonds between
complementary base
pairs
H- bonds between base pairs
3 H-bonds
Packaging
DNA in the
nucleus
DNA Replication


Weak hydrogen bonds between base
pairs hold DNA strands together.
Each chain in the helix is a
complimentary mirror image of the
other.
– Double helix unzips and undergoes semiconservative replication.

Confirmed by Meselson-Stahl Experiment.
Bi-directional replication
Proofreading by DNA
polymerase III
Genes to Proteins

Producing proteins from genes is
known as gene expression
– DNA -
RNA -
Protein
 Gene
Expression - Use of information in
DNA to direct production of particular
proteins.
– Transcription - mRNA molecule is
synthesized from gene within DNA.
– Translation - mRNA used to direct protein
production.
DNA vs RNA
Transcription

The RNA copy of a gene used to produce a
protein is called messenger RNA (mRNA).

Essence of gene expression is reading
information encoded within DNA and
directing protein production.
– Each gene is read from a fixed promoter site
where RNA polymerase binds to DNA.
– RNA polymerase moves down DNA in threenucleotide steps (Codons).
– Each codon corresponds to a particular amino
acid.

64 possible codons
Transcription
Uracil replaces thymine
Production of mRNA (messenger RNA)
Is all of the DNA expressed?
Codons – triplet code
Translation – mRNA
>> polypeptide
Translation – the ribosome
Translation – the ribosome
Overview of translation