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WARM-UP:
What does DNA stand for?
What is the purpose of DNA?
What is the structure of DNA and
who figured it out?
DNA
CA Biology Standard- Genetics
4. Genes are a set of instructions encoded in the DNA sequence of
each organism that specify the sequence of amino acids in proteins
characteristic of that organism. As a basis for understanding this
concept:
• a. Students know the general pathway by which ribosomes
synthesize proteins, using tRNAs to translate genetic information in
mRNA.
• b. Students know how to apply the genetic coding rules to predict
the sequence of amino acids from a sequence of codons in RNA.
• c. Students know how mutations in the DNA sequence of a gene
may or may not affect the expression of the gene or the sequence
of amino acids in an encoded protein.
What is DNA?
• DNA (Deoxyribonucleic
acid) is the molecule that
contains the genes of living
things.
• It is in chromosomes inside
the nucleus of eukaryotic
cells. (In prokaryotes, it is
free-floating in the
cytoplasm.)
Animation: Human to DNA
• http://www.pbs.org/wgbh/nova/genome/dna
.html#
Rosalind Franklin
• In the 1950’s she used
X-Ray Diffraction to
take a picture of the
DNA molecule (longways).
What does Rosalind Franklin’s
picture of DNA show?
• There are 2 strands.
• The strands are
twisted around each
other in a double
helix.
• Nitrogenous bases
are at the center of
the molecule.
James Watson and
Francis Crick
• They were working on
figuring out the
structure of DNA but
couldn’t figure it out…
• When they saw Rosalind
Franklin’s Picture of
DNA, they figured out
that it was a…..
• DOUBLE HELIX!
What is the structure
of DNA?
• DNA is a double helix.
• The double helix is wound
around proteins called
histones.
• This forms a beadlike
structure called a
nucleosome.
• All packed together, this is
chromatin.
• Chromatin winds together to
form chromosomes.
Where is the ….
•
•
•
•
•
Double helix?
Histone?
Nucleosome?
Chromatin?
Chromosome?
DNA Structure
• http://www.sumanasinc.com/webcontent/ani
mations/content/DNA_structure.html
What is the
structure of DNA?
• Double helical ladder
• ‘Backbone’ of ladder
is made of the
sugar….
• Deoxyribose
• And…
• Phosphate!
What is the
structure of DNA?
The ‘rungs’ of the ladder
are made of
nitrogenous bases …
Pyrimidines (single ring):
• Thymine [T] and…
• Cytosine [C]
Purines (double ring):
• Adenine [A]
The purines and pyrimidines are held together by
• Guanine [G]
hydrogen bonds.
What is the
structure of DNA?
• A deoxyribose sugar,
a phosphate and a
base all together
make up a…
• NUCLEOTIDE!
Build a DNA Model
in Your Notebook
10 points
Cut out the
nucleotides and
match them up.
Paste the pieces of
DNA into your
notebook.
Answer the
questions.
“Row, Row, Row DNA”
• We love DNA
Made of nucleotides.
Sugar, phosphate and a base
Bonded down one side.
• Adenine and thymine
Make a lovely pair.
Cytosine without guanine
Would feel very bare.
http://www.wtvzone.com/REMEMBERTH
EN/kidsmidi1/rowrow.mid
Chargoff’s Rules
• He found that the percentage of thymine was
about equal to the percentage of adenine.
• And the percentage of guanine was about
equal to the percentage of cytosine.
• Thus, they always pair with each other!
CHARGOFF’s RULE =
BASE PAIRING RULE!
• Thymine always pairs with Adenine
T-A
A-T
• Cytosine always pairs with Guanine
C-G
G-C
Build a DNA Molecule
• http://learn.genetics.utah.edu/content/begin/
dna/builddna/
Why would DNA need to replicate
itself?
Why would DNA need to replicate
itself?
• When a cell divides and replicates itself during
mitosis, it needs to also replicate its DNA.
• During meiosis, the process of gamete
formation, DNA needs to be replicated to pass
genes onto offspring.
DNA Replication Overview
The DNA molecule
separates into 2
strands and then
produces 2 new
complementary
daughter strands
using the base-pair
rule. Each strand of
the double helix is a
template for the new
strand.
DNA Replication
1. The enzyme Helicase ‘unzips’ the double helix by
breaking the hydrogen bonds.
2. The enzyme DNA Polymerase joins individual
nucleotides together, making the new strand of DNA.
DNA Replication Animation
• http://highered.mcgrawhill.com/olc/dl/120076/micro04.swf
Paste the DNA strand into your
notebook and write the
complementary strand.
ATGGGCCTTAAACATTA
What is the difference between
DNA and RNA?
DNA
Structure
Function/Pr
ocesses
Nitrogenous
Bases
Type of
Sugar
Location in
Cell
Types
RNA
DNA
Structure
2-stranded double helix
Function/Pr
ocesses
Contains
genes/instructions for cell
Nitrogenous
Bases
Adenine, thymine,
cytosine, guanine
Type of
Sugar
Deoxyribose
Location in
Cell
Nucleus
Types
n/a
RNA
What is RNA?
• Ribonucleic acid
• Contains sugar ribose
(rather than
deoxyribose)
• Is single-stranded
rather than a double
helix
• Contains adenine,
cytosine, guanine and
the base uracil rather
than thymine
What is the function of RNA?
• RNA is involved in
protein synthesis 
making a gene into a
trait!
• It takes a copy of DNA
out of the nucleus
(because DNA is too big
to leave the nuclear
pores) and functions as a
‘working copy’ of DNA.
Types of RNA
• Messenger RNA [mRNA]:
RNA that makes a copy of
DNA and leaves the
nucleus
• Ribosomal RNA [rRNA]:
part of a ribosome, where
protein synthesis occurs
• Transfer RNA [tRNA]:
transfers amino acid to the
ribosome as it is needed in
the construction of a
protein
Types of RNA
DNA
RNA
Structure
2-stranded double helix
Single stranded
Function/Pr
ocesses
Contains
Involved in protein
genes/instructions for cell synthesis
Nitrogenous
Bases
Adenine, thymine,
cytosine, guanine
Adenine, uracil, cytosine,
guanine
Type of
Sugar
Deoxyribose
Ribose
Location in
Cell
Nucleus
Nucleus (mRNA),
ribosome and cytoplasm
(tRNA & rRNA)
Types
n/a
tRNA, mRNA, rRNA
HOW DO GENES BECOME TRAITS?
PROTEIN SYNTHESIS
(GENE EXPRESSION)
1. TRANSCRIPTION
2. TRANSLATION
Transcription
• The process where mRNA molecules are
produced by copying part of the DNA
molecule into a complementary sequence
How does transcription work?
• RNA polymerase binds to DNA and separates
the strands. It then uses one strand of DNA as
a template to assemble an RNA strand.
– RNA polymerase only binds to regions of DNA
called promoters, areas with specific DNA base
sequences.
RNA Editing
• Introns: sequences of DNA that do not code
for a gene
• Exons: sequences of DNA that DO code for a
gene
• When mRNA is created, the introns are cut
out of it and only the exons are kept!
Translation
• The process where the cell uses mRNA to
produce proteins. tRNA brings amino acids to
the ribosome to match up with the mRNA.
The Genetic Code
Codon: 3 nucleotide
bases that code for a
particular amino acid
(1 codon = 1 amino acid).
AUG is the start codon.
3 stop codons: UGA,
UAA, UAG.
Only 4 bases, but they
code for 20 different
amino acids (protein subunits)
HOW?
4x4x4= 64 possibilities
How does translation work?
1. After transcription, mRNA attaches to the
ribosome.
How does translation work?
2. Starting with the start
codon, AUG, in the mRNA
the proper amino acid is
brought to the ribosome
by tRNA. That amino acid
is attached to the
polypeptide chain. Each
tRNA molecule is specific
to an amino acid. It has an
anticodon that is
complementary to the
mRNA codon.
How does translation work?
3. Polypeptide bonds are
created between amino
acids, while bonds between
tRNA and the amino acid are
broken.
4. The process continues until
tRNA hits a stop codon and
the protein is assembled!
Protein Synthesis Wksht
15 points
REMEMBER:
mRNA codes for amino acids using codons.
tRNA brings the amino acids to mRNA using
anti-codons
Central Dogma Sing Along!
What is a mutation?
Mutations = changes in genetic material
• Mutations can be:
– Advantageous
– Deleterious
– Have no effect
• Mutations are usually random and spontaneous,
but they are sometimes caused by mutagens,
chemical or physical agents that cause mutations.
Types of Mutagens
• Chemical Mutagens
– Example: nicotine, smoke, pesticides, methane,
pollution
• Physical Mutagens
– Ultraviolet rays, radiation, extreme heat
• Biological Mutagens
– Bacteria, viruses
Mutagens
Mutagens that cause cancer are called carcinogens
because they cause unregulated cell growth.
Examples of carcinogens:
– Poisons
– Smoke in your lungs
– Pollution
– Radiation
Types of Mutations
What is the difference between these two
statements?
• My dog bit the cat.
• My dog bit the car.
This is a point mutation- a mutation involving
changes in one or a few nucleotides.
Types of Point Mutations:
• Insertion
• Deletion
• Substitution
Frameshift mutations are…
• When nucleotides are added or deleted,
causing the whole reading frame to be
shifted so that every amino acid is altered.
Gene Action/Mutations
15 points
Staple into notebook when finished.
Translating a DNA Message
Make a DNA Keychain
• Write a Key in your notebook.
– Phosphate = big gold bead
– Sugar = big green bead
– Adenine = silver tube bead
– Thymine = red tube bead
– Guanine = dark blue tube bead
– Cytosine = green tube bead
Instructions for DNA Keychains
• http://www.indiana.edu/~ensiweb/connectio
ns/genetics/beadproject/tpage.html