Download DNA

A. DNA— deoxyribonucleic acid; determines
an organism’s traits by controlling when
proteins in the body are made
1. Proteins and enzymes —control
most aspects of cellular function in an
organism
B. Structure of DNA
1. Made of long chains of nucleotides
a. 3 parts of a nucleotide:
- phosphate group
- simple sugar (deoxyribose)
- nitrogen base
b. 4 types of nitrogen bases:
- adenine (A)
- guanine (G)
- cytosine (C)
- thymine (T)
Adenine (A)
Guanine (G)
Cytosine (C)
Thymine (T)
c. Complementary base pairs:
- A pairs with T
- G pairs with C
Adenine (A)
Guanine (G)
Cytosine (C)
Thymine (T)
d. Nucleotides join together in long chains
to form nucleic acids.
2. All organisms are made up of the
same nucleotides, just in different
order
a. Example: All words are made
up of the same letters, just in
different order
A. Discovered by James Watson
and Francis Crick in 1953.
1. Double Helix — double
stranded, twisted ladder
shape of DNA
2. If DNA is a ladder:
a. Sugar and phosphate
groups form the
backbone or the sides
of the ladder
b. Nitrogen bases form
the rungs of the ladder.
James Watson and Francis Crick
3. Individual
nucleotides are
joined by covalent
bonds.
4. Nitrogen bases in
the middle of the
helix are joined by
hydrogen bonds.
B. How does DNA fit in the cell?
1. Think about it! The DNA strand can be
incredibly LONG! Human DNA molecules
contain up to 4,639,221,000 base pairs. That
means there is about 1-2 meters of DNA in
each cell. How can it be kept in such a small
area?
2. The solution:
a. Chromatin is made of DNA packed
around histone proteins.
b. During interphase, these are
dispersed and uncoiled. When cells
enter prophase, they pack tightly to
form chromosomes.
A. DNA Replication - Whenever a cell divides, the
DNA must be copied before it splits
1. DNA helicase, an enzyme, unzips the
double helix (breaks the hydrogen bonds) to
form two single strands still joined at the
replication forks.
Replication Fork
DNA helicase
Replication Fork
DNA helicase
2. DNA polymerase, an enzyme, adds new
nucleotides to each single strand according to their
complementary base pairs
a. DNA polymerase also “proofreads” for
errors
Replication Fork
Replication Fork
DNA polymerase
DNA helicase
DNA helicase
3. DNA Ligase, an enzyme, reseals the gaps
remaining in the sugar/phosphate backbone to
finish.
Replication Fork
Replication Fork
DNA ligase DNA polymerase
DNA helicase
DNA helicase
4. END RESULT: 2 new and identical molecules
of DNA are formed
a. 1 strand made of “old” DNA
b. 1 strand made of “new” DNA
New DNA
molecule
Original
DNA Strand
Free Nucleotides
New DNA
molecule
New DNA
Strand
Original
DNA Strand
Original DNA
DNA
Replication
5. Example Complementary Base Pairing
a. (Find each complementary base pair for
the strand of DNA)
A—C—T—A—G—A—C—C—T—A—G—T
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T G A T C T G G A T C A
6. Example of DNA Replication
a. (Unzip the following molecule of DNA, and write the two
new strands of DNA that would result from the replication)
b. Original DNA Molecule
C—G—T—C—A—T—C—G—C—A—A—T—G
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G—C—A—G—T—A—G—C—G—T—T—A—C
Molecule #1
C—G—T—C—A—T—C—G—C—A—A—T—G
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G—C—A—G—T—A—G—C—G—T—T—A—C
Molecule #2
C—G—T—C—A—T—C—G—C—A—A—T—G
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G—C—A—G—T—A—G—C—G—T—T—A—C
A. DNA- Double stranded nucleic acid that
is stored in the nucleus of the cell.
1. Gene- piece of DNA that controls a specific
trait
B. RNA - a single stranded nucleic acid found all
over the cell (nucleus, cytoplasm, and ribosome)
1. Made of long chains of nucleotides:
a. 3 parts of a nucleotide—
-phosphate group
- simple sugar (ribose)
- nitrogen base
b. 5 types of Nitrogen Bases
- adenine (A)
- guanine (G)
- cytosine (C)
- thymine (T)
- Uracil (U)
c. Complementary base pairs
- A pairs with U
- T pairs with A
- G pairs with C
d. Nucleotides join together in long chains to form
nucleic acids.
2. Three Types of RNA
a. Messenger RNA (mRNA)- carries the
information from the DNA in the nucleus to the
rest of the cell
Codon
b. Transfer RNA (tRNA)helps build proteins by
carrying amino acids to
ribosomes, following
instructions coded for in the
mRNA.
Transfer RNA
molecule
Amino
acid
Chain of RNA
nucleotides
 Each tRNA carries only
ONE type of amino acid
 The code of the tRNA is
complementary to the
mRNA.
Anticodon
c. Ribosomal RNA (rRNA)- the site of protein synthesis;
makes up the ribosome
C. DNA/RNA Comparison
Molecule
DNA
RNA
Sugar
Deoxyribose
Ribose
Structure
Double strand
Single strand
Nucleotides A, T, G, C
A, U, T, G, C
Adenine - thymine Adenine - uracil
Thymine - Adenine)
Location in Stays in the nucleus Leaves nucleus to
cell
ribosomes
D. Protein Synthesis - Using genetic information in
DNA to make proteins
DNA
transcription
RNA
Protein
translation
E. Steps of Protein Synthesis
1. Transcription - Process of
making mRNA from DNA
a. Why? DNA can’t leave nucleus but
RNA can
b. Steps of Transcription
1. RNA polymerase, an enzyme, unzips the double
helix of DNA inside the nucleus and uses it as a
template to create a complementary mRNA strand
2. RNA editing occurs
 Introns - sections of the DNA that don’t code for
proteins are cut from the mRNA
 Exons - sections of the DNA that code for
proteins are left on the mRNA
3. DNA rezips and mRNA leaves nucleus and goes to
the cytoplasm to find a ribosome for protein
synthesis
c. Example: Transcribe the DNA into mRNA.
ACCA TGACCTGAC TTAC
UGGUACUGGACUGAAUG
2. Translation: Making chains of amino acids
(proteins) by reading/translating mRNA codons
(a group of 3 nucleotides) in the ribosome
a. The amino acid sequence determines the
structure and function of proteins
codon
b. Steps of Translation
1. mRNA travels to ribosome with a message
from the DNA and attaches to the rRNA.
3.
2.
2.
1.
2. As each mRNA codon moves over the
ribosome, it is matched with its complementary
tRNA anticodon, which is carrying amino acids.
3.
2.
2.
1.
3. Inside the ribosome, peptidase, an enzyme,
helps form peptide bonds joining amino acids
to make proteins and tRNA is released to go
find another amino acid
3.
2.
2.
1.
c. Example: Translate the mRNA into proteins
(USE CODON CHART!)
 mRNA = A U G C A U G G A A G C U G A
 amino acid chain =
d. There are 20 amino acids created from
a combination of the 4 nitrogen bases
- Each mRNA codon specifies a
different tRNA anticodon to bring
amino acids to join to the protein
- Every different combination
Methionine Alanine
of amino acids forms new
proteins
Peptide
bond

Special Codons some codons
signal start or
stop
 AUG (methoinine) =
start building
protein
 UAA, UAG, and UGA
= stop building
protein
Stop
codon
3. Transcription/Translation Comparison
Process
Transcription
Translation
Location
In Nucleus
At the ribosome
Purpose
Turn DNA into
RNA
Turn RNA into
proteins
Molecules
involved
DNA, mRNA
mRNA, tRNA,
rRNA
A. Mutation - Mistake or change in DNA
sequence
1. The change in the DNA is HUGE since the codon is
changed
a. If the codons are affected, the amino
acids and proteins for the cell are also
affected.
B. Types of Mutations
1. Point Mutation - change in a SINGLE
base pair in DNA
a. Substitution Mutation - one nitrogen base
is replaced with another
- Example:
ACTAGGCAC to
ACTAGTCAC
- Results in a change of one codon
Normal
mRNA
Protein
Point
mutation
mRNA
Protein
b. Frameshift Mutation - ONE base is
added or deleted from DNA, and it
shifts the reading of codons
- Example: Addition Mutation: ACTAGGCAC to
ACTAGGGCAC
Deletion Mutation: ACTAGGCAC to
ACTAGCAC
- Results in EVERY codon after the
mutation to change.
- Original Protein: Meth-Lys-Phenyl-Gly-AlaLeu
- Mutated protein: Meth-Lys-Leu-Ala-HistCys
Without mutation
Frameshift mutation
mRNA
Protein
Deletion of U
Normal
Substitution
(Point)
Addition
(Frameshift)
Deletion
(Frameshift)
2. Which type of mutation is more serious?
a. Frameshift - it affects EVERY amino
acid/protein after the mutation
Frameshift mutation
mRNA
Protein
Deletion of U
3. Chromosomal mutations - Structural
changes in chromosomes
a. Are especially common in plants.
4. Four Types of Chromosomal
Mutations
a. Deletion -part of a
chromosome left out (usually
deadly)
A B C D E
F G H
A
Deletion
B C E
F G H
b. Duplication/Insertion: chromosome part
breaks off and reattaches to its sister
chromatid
Insertion
A B C D E
F G H
A B C B C D E F G H
Insertion
*Genes B and C were inserted into
the chromosome*
c. Inversion - chromosome part
breaks off and reattaches backwards
A B C D E
F G H
A D C B E
Inversion
F G H
d. Translocation - chromosome part breaks
off and adds to a different chromosome
Translocation
Inversion
Insertion
Deletion
Translocation
C. Causes of Mutations
1. Spontaneous/Random mutations–
◦ Some mutations just happen, ( amistake during DNA
replication, transcription, mitosis, meiosis).
 a. These lead to evolution.
2. Mutagen - Any agent that causes a change in
DNA
 a. Include radiation (uv or nuclear radiation) and chemicals
(asbestos or formaldehyde)
 B. Environmental agents