Download DNA Structure Notes

Ch. 9 &10
DNA, RNA & Protein Synthesis
I. DNA-Deoxyribonucleic Acid
A. In 1953 James Watson and Francis Crick built a model
of DNA based on x-rays taken by Rosalind Franklin
B. DNA Structure
1. Shape- Double Helix
(winding staircase)
2. Made of Repeating
Nucleotides: 3 parts
a) Phosphate group
b) Deoxyribose Sugar
c) Nitrogen base
C. Nitrogen Bases- 2 types
1. Purines- 2 carbon rings in structure,
Adenine & Guanine
2. Pyrimidines- 1 carbon ring in structure,
Thymine & Cytosine
D. A Purine is always paired with a pyrimidine, held
together by weak H bonds
A=T
G C
2 stars
3 stars
E. Bases are always attached to deoxyribose sugars
DNA drawing
P
S -C =
P
S -G =
P
S -T =
P
S -A
P
S -C
P
S -G
Right-hand rule= nitrogen
bases only bond on R sideresults in 2 opposite running
strands
http://www.ted.com/talks/james_watson_o
n_how_he_discovered_dna.html
QUIZ
1.
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Name the people who made the first model of DNA.
What are the 4 nitrogen bases (words not letters)?
What are the three parts that make up a nucleotide?
What is DNA’s shape?
Which bases are pyrimidines?
Which are doubled-ringed, purines or pyrimidines?
What type of bonds hold the nitrogen bases together in the
middle of the DNA strand?
How many bonds form between A and T?
How many bonds form between G and C?
Why is a DNA molecule said to be complementary?
What is the complementary strand of DNA for ACATGG?
Answers-18 pts total
1.
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2-Watson and Crick
4-Adenine, Guanine, Cytosine, Thymine
3-Phosphate, Sugar, Base
1-Double helix/winding staircase
2-Thymine, cytosine
1-Purines
1- Hydrogen Bonds
1- 2 hydrogen bonds
1- 3 hydrogen bonds
1- by knowing the nitrogen bases on one side of the
DNA we can determine the sequence of bases for the
other side of the DNA
1-TGTACC
II. DNA Replication
A.
B.
Replication- the process of copying DNA to
get ready for cell division, occurs in the
nucleus
Steps
1.
Helix unwinds and an enzyme (DNA helicase)
breaks the Hydrogen bonds between the bases
2.
Enzyme (DNA Polymerase) moves along each
strand and adds the complementary base to each ½
strand; Polymerase also proofreads its work
3. Strands Detach and 2 new identical
strands are formed
4. Process is considered a semi-conservative
process because the strands are ½ original, ½
new DNA
III. Protein Synthesis
A. The process of producing proteins made of
amino acids from the instructions provided
by the DNA
B. RNA-(ribonucleic Acid) gets instructions to
ribosome to make proteins
1.
2.
3.
4.
Single Strand
Ribose instead of
Deoxyribose Sugar
No Thymine, Uracil
replaces Thymine
3 Types of RNA
a) Messenger RNA- (mRNA)- copy of
information from DNA
- every 3 nitrogen bases make a codon,
these code for a specific amino acid
b)Transfer RNA- (tRNA)- transports
amino acids, has a matching anti-codon
-3 nitrogen bases make an anticodon
c) Ribosomal RNA- (rRNA)- makes up
ribosomes
***2 steps for Protein Synthesis
C. Transcription-unwinds DNA and makes a
copy called mRNA, occurs in the nucleus
D. Translation- mRNA and tRNA build a
protein out of amino acids.
Occurs in the cytoplasm at a ribosome
Animations

http://www.stolaf.edu/people/giannini/flashan
imat/molgenetics/dna-rna2.swf

http://www.stolaf.edu/people/giannini/flashan
imat/molgenetics/transcription.swf
http://www.stolaf.edu/people/giannini/flashanim
at/molgenetics/translation.swf
IV. Mutations- a change in the DNA
of a gene, occurs during replication
3 types:
1. Substitution- one nucleotide is replaced with a
different nucleotide
2. Insertion- one or more nucleotides are added
3. Deletion- one or more nucleotides are deleted
Humans inherit 3 billion base pairs of DNA
from each parent. That means that each
cell has 6 billion pairs that can be a target
of a mutation. It is estimated that mutations occur in
about 1 in every 50 million
nucleotides. That means that each
new cell could have some 120
Mutations can:
mutations
-have no effect (occur in the “junk DNA”, about 97% of DNA
does not encode for anything- that we know of)
-be silent-mutations that code for the same amino acid
-cause disease such as Cystic Fibrosis, Retinoblastoma,
Sickle Cell anemia
-occur in gametes (egg & sperm)- can result in Fragile X
syndrome and Huntington’s disease