Download Molecular Genetics Notes

Molecular Genetics
Question???????
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What IS a gene or trait? In the case
above, what are freckles?
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Freckles are PROTEINS!!!!
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One gene = One protein!!!!!
Let’s Review
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Protein:
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Made up of amino acids
Made in the ribosomes
Examples of Proteins:
Hormones
Antibodies
Enzymes
A. Structure of DNA
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DNA – Deoxyribonucleic Acid
* discovered in 1953 by Watson and Crick
* Double Stranded molecule that forms a
double helix
* Basic Unit of DNA is a nucleotide
A Nucleotide
The nucleotide symbols for DNA
are:
= Phosphate Group
= Deoxyribose (5 carbon sugar)
= Nitrogenous Base
The bases in DNA always pair
according to the following rules:
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A with T: the purine adenine (A) always
pairs with the pyrimidine thymine (T)
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C with G: the pyrimidine cytosine (C)
always pairs with the purine guanine (G)
Function of DNA
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Instructs the cell to
make new proteins
Passed down to
offspring
B. DNA Replication
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Replication – Process in which DNA makes
an exact copy of itself
This occurs prior to mitosis (cell division)
for growth or repair
Steps:
1. Occurs in the nucleus
2. DNA must “untwist and unzip”
3. Free nucleotides pair up to the 2 new
single stranded DNA (complementary
pairing A-T, C-G)
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http://www.youtube.com/watch?v=hfZ8o9
D1tus
http://www.youtube.com/watch?v=dIZpb
93NYlw&feature=related
http://www.youtube.com/watch?v=d1UPf
7lXeO8&feature=related
DNA Replication Review…..
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What is it?
Making an exact of itself
Where does it occur?
Nucleus
Why?
Mitosis and Meiosis
When?
Growth, Repair and Reproduction
Steps of Replication
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DNA untwists and unzips
- Bases are held together by
HYDROGEN BONDS
- Each single strand becomes a
template, or pattern, for a new strand of
DNA
A–T
T–A
G–C
G–C
C–G
T–A
Original DNA
A-T
T-A
G-C
G-C
C-G
T-A
A
T
G
G
C
T
-
T
A
C
C
G
A
2 Replicated DNA
Nucleotides are brought to the “unzipped”
section and attach following the base pairing rules

http://www.pbs.org/wgbh/aso/tryit/dna/s
hockwave.html
How does DNA direct the
production of proteins???
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The function of DNA is to tell the cells
what proteins to make
Where are the proteins made?
at the ribosomes in the cytoplasm
Dilemma!!! DNA IS TRAPPED INSIDE OF
THE NUCLEUS
SOLUTION – RNA (Ribonucleic Acid)
RNA - Ribonucleic Acid
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A Nucleic Acid made up of a long chain of
nucleotides
contains the sugar RIBOSE (NOT deoxyribose)
Bases – Cytosine pairs with Guanine
Adenine pairs with URACIL (NOT Thymine)
RNA is capable of copying the DNA and bringing
the genetic message to the ribosome where
proteins are produced
RNA Structure
Ribose
Sugar
Phosphate
Group
Nitrogenous
Base
Comparison of DNA and RNA
Structure
Bases
Location in the
cell
Sugar
DNA
RNA
Double
Single
stranded
A-T, C-G
stranded
A-U, G-C
Nucleus
Nucleus and
cytoplasm
Deoxyribose
Ribose
3 Types of RNA
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mRNA – Messenger RNA – brings genetic
code from DNA to ribosomes to synthesize
protein (from nucleus to cytoplasm)
tRNA – Transfer RNA - carries amino acids
to ribosome
rRNA – Ribosomal RNA – makes up
ribosomes
Protein synthesis begins in the
nucleus by…..
1.
The DNA must untwist and unzip. One strand
will serve as a TEMPLATE or pattern
T-A
T
A-T
A
THIS SINGLE
T-A
T
STRAND IS
T-A
T
USED AS A
C-G
C
TEMPLATE
G-C
G
2. Transcription of the gene (DNA to
RNA) - how the DNA code gets to the
ribosomes
Messenger RNA (mRNA) is formed. RNA nucleotides
attach to DNA strand
Ex. T - A
A-U
Codon - group of 3 nucleotides
T-A
on mRNA. Codes for a
T-A
specific amino acid
C-G
Transcription - “to make a copy of”
G-C
how the DNA code gets to the
ribosomes
3.
4.
The mRNA strand is now a copy of the
DNA strand
Strand of mRNA detaches from DNA and
travels to the ribosome in the cytoplasm
AUA
AGC
.
RIBOSOME
REVIEW OF TRANSCRIPTION
Transcribe means to make a copy of
 Steps:
1. DNA untwists and unzips
2. Free nucleotides are brought to the
unzipped DNA following the base pair
ruling
3. mRNA strand is formed to be carried out
of the nucleus
DNA Base
A
T
C
G
G
T
A
T
C
G
A
RNA Complimentary
Pair
U
A
G
C
C
A
U
A
G
C
U
Now that we have the genetic code at the
ribosome, we are ready to synthesize (make)
proteins (enzymes, hemoglobin, etc.)
5. Translation of the Gene.
Transfer RNA (tRNA) - shuttles the correct
amino acid to the ribosome and the
correct protein begins to be assembled
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Anticodon - 3 nucleotides on the tRNA that
match the codon.
If the codon is CUA the anticodon must be..
GAU
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Translation - message from mRNA is
translated to tRNA to bring the specific
amino acid to the ribosome
Practice Protein Synthesis
DNA:
mRNA
tRNA
Amino
Acid
TAG
AUC
UAG
Ile
GCA
CGU
GCA
Arg
TTA
AAU
UUA
Asn
Amino Acids are based on the
codon NOT the anticodon
Review
1.
2.
3.
4.
5.
Steps
Transcription occurs in nucleus (DNA to mRNA)
Single stranded mRNA moves OUTSIDE the
nucleus to the ribosome
mRNA attaches to the RIBOSOME, which reads
the codon
tRNA’s anticodon matches to the codon and
brings Amino Acids to the ribosomes
(translation)
Amino acids bond together to make a protein
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Every 3 bases code for an amino acid
This code is “universal” = same for all
organisms
Codon - group of 3 bases (nucleotides)
Total # of amino acids known = 20
Protein Synthesis
DNA Code
AAA
ATC
GAC
CTG
AGT
TTA
GGA
CCA
mRNA
tRNA
Amino Acid
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http://www.pbs.org/wgbh/aso/tryit/dna/s
hockwave.html
E. Nature vs. Nurture
The environment and Heredity
There is an interaction with the environment
and certain genes are expressed while
others are hidden