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Chp 12: DNA & Gene Expression
1865 - Mendel
1900 - Morgan - Fruit flies reveal Mendel’s principles
1900 - Garrod - human alkaptonuria follows Mendel’s principle
Million $ question, What holds the hereditary information?
Morgan proposed chromosomes (colored bodies that occur
in pairs)
1928 - Griffith Transformation experiments
1944 - Oswald Avery’s analysis &
manipulation of transformation extract
(denaturing different organics using
enzymes - only extract exposed to DNA
destroying enzymes loses ability to
transform)
1952 Hershey & Chase
Experiments with viruses composed of DNA & protein grown in Sulfur isotopes &
Phophorus isotopes - Phosphorus
isotopes found in host cell
Million $ question - How does DNA carry hereditary info
What would scientists likely need to know in order to
answer this question?
Chemical Composition - Chargaff
Nucleotides with nitrogenous bases
4 types of bases
Rosalind Franklin - 1952 - X-ray diffraction studies
Two stranded
chemical
Equal distance
between two
strands
1953 - Watson & Crick Proposal
Double Helix - bound at the bases
complimentary base pairing
maintains width, holds strands
together and ultimately establishes
a code
Nucleotide
Phosphate
5 Carbon Sugar
Deoxyribose
Nitrogenous Base
•Adenine
•Guanine
•Cytosine
•Thymine
Twist this structure to get a double helix
Bases must be readily available to make the nucleotides. Plants
assemble the bases from nutrients in the soil. Animals get their
nucleotides ready made in what they eat. Inadequate supplies will
lead to stunted growth or malnutrition diseases.
DNA Replication
•
•
•
•
Occurs during the S-Phase
Involves the action of
special enzymes
Semi Conservative
Makes mitosis possible
Enzymes initiate the
process
•Helicase - breaks bonds
between bases
•Primase - lays down a short
sequence of RNA nucleotides
that enables DNA Polymerase
to begin replication
•DNA Polymerase - organizes
complimentary nucleotides in
order to assemble a new DNA
strand
•Ligase - glues open ends of
DNA where primers are
removed
•Binding Proteins maintain
single strands
Animation
Many Replication bubbles can be seen on a Single DNA at once
Even at the rate of hundreds of base pairs per second it takes hours
to replicate the human genome. (base pairs in the billions)
DNA holds code which determines cell function
Cell Function determines cell/tissue characteristics
Tissue function determines organism characteristics
How is the DNA code translated into specific cell function?
DNA controls the production of proteins, the types of
proteins present or not present determines cell / tissue
function (lactose intolerance, hemophilia, sickle cell
anemia……)
Proteins are composed of long chains of amino acids
There are 20 different amino acids. The number, type and
Amino Acids
sequence in which they are linked together determines the proteins
function. Change the sequence, type, or number of amino acids in
a protein you change the function.
Amino Acids without water sensitive R-groups
Interactions between adjacent amino acids produces spiral or pleating
Interactions between R-groups forms bends & folds
Two or more amino acids chains may hook up to form functional protein
Computer modeling enables scientists better understand
protein structure
The production of protein by DNA involves a two step
process and requires the presence of three different types
of RNA (all of which are assembled by DNA)
The DNA functions as the boss and the RNA as the
workers. The code for a particular protein is held by the
DNA. RNA converts the code into specific proteins
Plants assemble their amino acids from nutrients acquired from the
soil. How do animals acquire their amino acids?
Biologists believe that RNA was the first information storing
chemical used by primitive life forms and that it quickly was
replaced by DNA. Why is DNA better at storing information?
DNA & RNA are chemically and physically different. It is their
difference in chemical and physical properties that enable them to
have different functions.
DNA
Only in the nucleus
Double stranded
A-T & G-C base pairing
Deoxyribose Ribose Sugar
RNA
Nucleus & cytoplasm
Single stranded
A-U & G-C base pairing
Ribose Sugar
Transcription Animation
M-RNA
T-RNA
R-RNA
Translation Animation
Transcription
Complimentary
base pairing insures
an accurate writing
of the code.
The use of RNA
nucleotides insures
that the nucleic acid
is to function in the
cytoplasm
The order of the
nucleotides defines
its function (m-RNA,
t-RNA, r-RNA)
Animation
Translation:
The M-RNA that was made by the DNA leaves the
nucleus and associates with R-RNA, T-RNA, and initiator
proteins to start the production of protein
Animation
The M-RNA can have many ribosomes be attached at
once (poly ribosomes)
Which ribosome has is the most recent to have attached to the M-RNA?
M-rna codon calls for a complimentary t-rna
anticodon
Biologists have deciphered the code of life- m-RNA codon chart
To Conserve energy and raw materials, there are several levels of
control that insure that gene expression only occurs when needed.
1- DNA Structure
can Regulate gene expression
2- Activation or Blocking Promoter Sites
3- M-RNA Processing
can regulate gene expression - processing may not begin until key
chemical conditions have been established
4- Protein Processing
Proteins that are
asembled may require
specific conditions to
be establishjed before
they take on their
active form. This also
helps to regulate gene
expression
Web Links For DNA/RNA Review