Download DNA - Jordan High School

UNIT 6 – DNA
Chapters 12 & 13
12.1: The Role of DNA
The Role of DNA
• Storing
information—genes found within
DNA control cell functions
• Copying
information—all genetic
information copied before cell division
• Transmitting
information—new cells get
copies of DNA
12.2: The Structure of DNA
The Components of DNA
• DNA
•
is composed of chains of nucleotides
Each nucleotide consists of a sugar
(deoxyribose), a phosphate group, and a
nitrogenous base
• DNA
•
has 4 kinds of nitrogenous bases:
Adenine (A), Guanine (G), Cytosine (C),
Thymine (T)
• Nucleotides
bond between sugar of one
nucleotide and phosphate of another
•
Nitrogenous bases stick out sideways
Solving the Structure of DNA
• Rosalind
Franklin used X-rays to show DNA
was twisted into a helix shape
• James
Watson & Francis Crick used
Franklin’s work to show DNA as a double
helix
The Double-Helix Model
• DNA
consists of 2 strands twisted around
each other
• Nitrogenous
bases joined by hydrogen
bonds in the center of the double helix
• Base
pairing—nitrogenous bases only pair
with certain bases
•
•
Adenine (A) with Thymine (T)
Guanine (G) with Cytosine (C)
12.3: DNA Replication
Copying the Code
• Each
strand of DNA has the information to
make copies of the other strand
• Replication—the
process that duplicates
DNA
•
•
DNA separates into 2 strands
Each strand acts as a model for a new strand
• Process
1.
2.
of replication
Two strands of DNA “unzip” in nucleus
New strand forms by adding base pairs to
“parent strand” of DNA
•
If A is on parent strand, a new T pairs
with strand; C with G; etc.
• Replication
produces 2 DNA molecules
identical to each other
•
Half of DNA is old strand, half is new strand
• Enzymes
•
•
are used to help replication
Enzymes “unzip” DNA to begin replication
DNA polymerase joins individual nucleotides
to produce a new DNA strand and proofreads
DNA strand
13.1: RNA
The Role of RNA
• RNA
(ribonucleic acid)—nucleic acid that
produces proteins from DNA’s genetic
code
• Differences
•
•
•
between RNA & DNA:
RNA has ribose (not deoxyribose)
RNA is single-stranded (not double-stranded)
RNA contains Uracil (U) (instead of thymine)
• Functions
•
•
•
of RNA:
Messenger RNA (mRNA)—carry information
from DNA to other parts of the cell
Ribosomal RNA (rRNA)—compose ribosomes
Transfer RNA (tRNA)—transfers amino acids
to ribosome to build proteins
RNA Synthesis
• Transcription—production
of RNA
molecules using segments of DNA
• Uses
the enzyme RNA polymerase
• Process
1.
2.
3.
4.
of transcription
DNA strands separated in nucleus
One strand of DNA used as a template for
RNA strand
Uracil (U) pairs with A instead of T
•
G and C pair normally
Messenger RNA (mRNA) strand leaves
nucleus
Transcription Animation
13.2: Ribosomes & Protein Synthesis
The Genetic Code
• RNA
contains code from DNA for making
proteins
• Genetic
code—series of three letters (A, C,
G, or U) that forms an amino acid
•
Codon—three-letter series in mRNA
• Codons
form a code for different amino
acids
• AUG
= start codon (starts protein
synthesis)
Translation
• Translation—decodes
an mRNA message
into a protein
•
Uses ribosomes & tRNA molecules
• tRNA
•
•
molecules join with mRNA molecules
Carries one amino acid
tRNA has an anticodon—three letters
complementary to codon
• Process
1.
2.
3.
4.
5.
of translation
mRNA strand attaches to ribosome
tRNA anticodon binds to “start” codon
(AUG) on mRNA
Another tRNA binds to mRNA strand
Amino acid on first tRNA transferred to
second tRNA, forming a protein chain
Process continues until “stop” codon is
reached
Translation Animation
13.3: Mutations
Types of Mutations
• Mutations—changes
in genetic
information
•
Result from changes in single gene or
changes in whole chromosomes
• Point
mutations—changes in one or a few
nucleotides
•
•
•
Substitutions—one base changed to another
(may have no effect)
Insertions—one base added (major effect)
Deletions—one base deleted (major effect)
• Insertions
& deletions also called
frameshift mutations—change the entire
genetic message after the mutation
Effects of Mutations
• Mutagens—chemical
or physical agents
that cause mutations
•
Ex: pesticides, tobacco smoke, radiation
• Harmful
effects of mutations: genetic
disorders, cancers, lack of cell function
• Helpful
effects of mutations: resistance to
chemicals, larger & stronger crops