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DNA & Genes
Chapter 12
DNA, RNA, &
Protein Synthesis
I.
DNA Molecule of Heredity
A. Structure
• DNA (polymer) is a long molecule made up
of Nucleotides (monomers)
• A Nucleotide consists of:
– Deoxyribose (a 5-carbon sugar)
– a phosphate group
– One of 4 Nitrogenous bases (contain nitrogen)
• Adenine (A)
PURINES
• Guanine (G)
• Cytosine (C)
PYRIMIDINES
• Thymine (T)
•The nitrogenous bases of DNA (purines –
double ring / pyrimidines single ring)
DNA
• Deoxyribonucleic acid
• Deoxyribose is sugar
• Nitrogenous bases:
Adenine binds with Thymine
Cytosine binds with Guanine
One nucleotide of
Structure of DNA (cont.)
• DNA is like a twisted ladder:
– Rungs: complementary base pairs (A=T, G=C)
– Uprights: deoxyribose and phosphate groups
• Your Turn: Match this DNA base sequence with its correct
complementary DNA bases:
• T-C-G-A-A-C-T
• A-G-C-T-T-G-A
DNA….who cares
Is used to determine
Is used to catch
criminals
the paternity of
Children on shows such as:
Is used to make
genetically modified food Is used to compare
similarities between
species
Is used to make
antibiotics and
vaccines
History: Griffith and Transformation
• Year: 1928
• Examined 2 strains of
pneumonia bacteria
– Rough
– Smooth
• Injected mice with bacteria to
see if they would develop
pneumonia
• Discovered transformation
– Took the heat killed bacteria
and combined it with the
harmless bacteria, and mice
developed pneumonia
History: Avery & DNA
• 1944
• Used Griffith’s
experiment. He wanted to
know which molecule in
the heat-killed bacteria
was important in
transformation
• Avery used enzymes to
discover that DNA was
the molecule that allowed
transformation to happen
History: Hershey-Chase
• 1952
• The Hershey-Chase experiment
used viruses known as
bacteriophages.
• Question: Wanted to know
which part of the virus, protein
or DNA, entered the infected
core of bacterium. Preformed
the experiment by using
radioactive markers
• Concluded, that the genetic
material was DNA
B. History
. CHARGAFF (1949):
discovered that the % of
Cytosine and Guanine
were about the same in
DNA; the same was
true about Adenine and
Thymine
– This suggests BASE
PAIRING………..
that C bonds with G
and A bonds with T!
Source of
DNA
A
T
G
C
Streptococcus
29.8
31.6
20.5
18.0
Yeast
31.3
32.9
18.7
17.1
Herring
27.8
27.5
22.2
22.6
Human
30.9
29.4
19.9
19.8
Purines
Phosphate group
Pyrimidines
Deoxyribose
History (cont.)
2. Wilkins and
Franklin(1952): took
X-Ray photographs of DNA
which suggested a twisted,
helical structure, 2 strands, and
bases in the center
3. Watson and Crick
(1953): using all the research
to date, discovered the structure
for DNA: A DOUBLE HELIX
(with sugar-phosphate backbones
and bases on the inside held
together by H bonds)
More DNA info
• DNA contains information that
determines an organism’s
function and appearance
• Some DNA codes for proteins
• DNA is located within genes
(sections of a chromosome)
inside of the nucleus of every
cell
Wait a minute…
Does that shape remind you
of any other shape you may
have seen before?
How about this portion of an
apple?
DNA Flo Rider Featuring – TPain-less
Shawty got them apple bottom genes with the DNA (NA)
Nucleotides twisted that way
They start to fold (they start to fold)
Next thing you know
Shawty got chro mo so o o o o omes
The A’s bond with the T’s and the C’s bond with the G’s (with the G’s)
Hydrogen bonds in the double helix
They start to fold (they start to fold)
Next thing you know
Shawty got chro mo so o o o o omes
DNA Replication
• DNA opens up and makes a complete copy
of itself – necessary during mitosis and
meiosis
• New nucleotides float in and pair in a
complementary fashion – A to T, C to G
and vice versa…
Figure 16.7 A model for DNA replication: the basic concept (Layer 1)
Figure 16.7 A model for DNA replication: the basic concept (Layer 2)
Figure 16.7 A model for DNA replication: the basic concept (Layer 3)
Figure 16.7 A model for DNA replication: the basic concept (Layer 4)
Semi-conservative process…
C. DNA Replication:
making more DNA during the S Phase of the Cell Cycle
(in the nucleus)
1. The enzyme helicase unwinds DNA double helix
(breaks hydrogen bonds btwn. bases) & a
replication fork is created.
(Each old DNA strand will act as a template for 2
new strands to be added on)
2. Enzyme called DNA Polymerase binds to
replication fork and adds free nucleotides to each
old strand of DNA
3. DNA Polymerase remains attached until 2 new
DNA strands are created; it “proofreads” the
strands to minimize error in the process.
Chromosome Structure
Chromosome
Nucleosome
DNA
double
helix
Coils
Supercoils
Histones
Go to
Section:
DNA
Animation
DNA Replication (cont.)
• Diagram of DNA Replication:
II.
DNA  Protein
A. RNA
• RNA: Ribonucleic Acid; used to make proteins / Single-stranded
-RNA (polymer) made of nucleotides (monomer):
-Ribose = 5 C sugar + Phosphate group + N Base
4 bases:
•
•
•
•
Cytosine (C)
Guanine (G)
Adenine (A)
Uracil (U) – NO THYMINE in RNA!
– 3 types of RNA:
1. messenger RNA (mRNA) – single stranded
transmits info from DNA to protein syn.
2. transfer RNA (tRNA) - single stranded/
20 or more varieties ea. w/ ability to bond to only
1 specific AA
3. ribosomal RNA (rRNA) – globular / major
component of ribosome
B. Protein Synthesis (overview)
• 2 Stages in making proteins:
1) Transcription – using DNA template to
make mRNA strand
2) Translation – using mRNA strand to
create polypeptides
DNA
Transcription
RNA
Translation
Protein
1. Transcription
• The Goal of Transcription is to produce a singlestranded mRNA helix that contains information
from DNA to make proteins
• How it’s done: (This happens in the Nucleus!)
1. DNA strand unwinds/unzips complementary DNA strands
2. Enzyme called RNA Polymerase binds to DNA “promoter”
regions and “plugs in” complementary RNA nucleotides to the
DNA template.
– Example = DNA Template: ATTGGCAGT
new RNA Strand: UAACCGUCA
Transcription (cont.)
Transcription (cont.)
3. Once produced, this pre-mRNA
strand breaks away when RNA
polymerase reaches a sequence of
bases on DNA that act as a stop
sign.
• The finished product (mRNA)
moves out of the Nucleus through a
nuclear pore into the cytoplasm.
4. 2 DNA complementary strands
rejoin
2. The Genetic Code
• How do we get proteins from mRNA
strands?
• The mRNA strand must be read in groups
of 3 nucleotides, called a CODON.
• Different Codons translate for different
Amino acids.
Codons in mRNA
Codons in mRNA
• “Start” codon = AUG (Methionine)
• “Stop” codons = UAA, UAG, and UGA
• Example:
• mRNA Strand:
• U-C-A-U-G-G-G-C-A-C-A-U-G-C-U-U-U-U-G-A-G
methionine
glycine
threonine cysteine phenylalanine STOP
3. Translation
• The Goal of Translation is to “translate” these
mRNA codons into their amino acids to form a
polypeptide.
• How it’s done:
1. mRNA strand attaches to a ribosome (rRNA)
2. Each mRNA codon passes through ribosome
3. Free-floating Amino Acids from cytosol are brought to
ribosome by tRNA
4. Each tRNA has an anticodon to match up to mRNA
codons
5. Amino Acids are joined as tRNA keeps bringing them
6. Polypeptide chain grows until “stop” codon is reached
Translation (cont.)
• Translation
1st. mRNA strand attaches to a ribosome (rRNA)
Translation (cont.)
• Translation
2nd, Each mRNA codon passes through ribosome
Translation (cont.)
3rd, Free-floating Amino Acids from cytosol are brought to ribosome
by tRNA
• Translation
Translation (cont.)
• Translation
4th, Each tRNA has an anticodon to match up to mRNA codons
Translation (cont.)
• Translation
5th, Amino Acids are joined as tRNA keeps bringing them
Translation (cont.)
• Translation
. Polypeptide chain grows until “stop” codon is reached
III. Genetic Changes: Mutations
A. Types of Mutations
1. Gene Mutations: changes in nucleotides
– Point Mutations
– Frameshift mutations
2. Chromosome Mutations: changes in # or structure
of chromosome
–
–
–
–
Deletion
Insertion/Duplication
Inversion
Translocation
1. Gene Mutations
a. Point Mutation: the
substitution, addition or
removal of a single
nucleotide
b. Frameshift Mutations:
types of point mutations
that shift the “reading
frame” of the genetic
message
Example of Point Mutation
Induced Point mutation in
growth hormone gene
causes semi-dominant
dwarfism & obesity
*image borrowed from www.science.ngfn.de/6_164.htm
B. Chromosome Mutations
1. Deletion……………………………
2. Insertion/Duplication…………
3. Inversion…………………………
4. Translocation…………………….
• A chromosomal mutation involves changes in the number
or structure of chromosomes. Chromosomal mutations
may change the locations of genes on chromosomes and
even the number of copies of some genes.
• Deletion involves the loss of all or part of a
chromosome.
• The opposite of a deletion is a
• Duplication, in which a segment of a chromosome is
repeated.
• When part of a chromosome becomes oriented in the
reverse of its usual direction, the result is an Inversion.
• A Translocation occurs when part of one
chromosome breaks off and attaches to another, nonhomologous, chromosome. In most cases, nonhomologous
chromosomes exchange segments so that two
translocations occur at the same time.
• A chromosomal mutation involves changes in the number
or structure of chromosomes. Chromosomal mutations
may change the locations of genes on chromosomes and
even the number of copies of some genes.
• Deletion involves the loss of all or part of a
chromosome.
• The opposite of a deletion is a
• Duplication, in which a segment of a chromosome is
repeated.
• When part of a chromosome becomes oriented in the
reverse of its usual direction, the result is an Inversion.
• A Translocation occurs when part of one
chromosome breaks off and attaches to another, nonhomologous, chromosome. In most cases, nonhomologous
chromosomes exchange segments so that two
translocations occur at the same time.
Gene Regulation in Prokaryotes
The lac operon enables the production of lactose-processing enzymes in E.
coli, but only when needed.
• In the presence of lactose, the
• In the absence of lactose, the
repressor is inhibited from
repressor protein binds to the
binding with the operator; this
operator on DNA and inhibits
all ows transcription to take
transcription of lactoseplace to produce lactoseprocessing enzymes.
processing enzymes.