Download DNA Replication

UNIT 6: DNA
BIG IDEA: DNA contains the genetic
information to produce proteins but
must first be converted to RNA to do
so
http://evolution.berkeley.edu/evolibr
ary/article/mutations_02
Why do cells need DNA?
• DNA contains the information
cells need to function and live.
• Two main roles for DNA are
1. Storing genetic info and to
2. “Read” and translated to make
proteins
DNA Replication
“It has not escaped our notice
that the specific pairing we have
postulated immediately suggests
a possible copying mechanism for
the genetic material”
~Watson and Crick
Why do cells need to replicate
(copy) their DNA?
• To make new cells and
make sure all new cells
have a complete set of the
genetic info
How do cells replicate their DNA?
1. The DNA double
helix is
unwound by an
enzyme.
2. Another enzyme
moves down the
2 original DNA
strands and
adds
complementary
nucleotides.
3. Two separate
DNA molecules
are formed,
each with
one new strand
and one old
strand.
Replication Stats
• 6 billion base pairs per cell.
• All are replicated in a few hours.
• Mistake happens one per billion
nucleotides.
Mistakes = Mutations
• Mutations are changes in the base
sequence of the DNA molecules.
• This can have serious affects on
genes and the functions of cells.
• Cancer is caused by mutations in
DNA.
Mutagens
• Physical or chemical factor that
increases the frequency of
mutations.
• Examples: UV rays, X-rays,
smoking
3 Types of Mutations
• Insertion
• Deletion
• Substitution
MUTATIONS
DO NOW:
• What words do you think of
when you hear the term
mutations?
Three Types
1. Substitute: one
nitrogen base is
substituted for
another in the
DNA strand
• Normal DNA:
TAGCGCTA
ATCGCGAT
Mutated DNA:
TAGCGCTA
ATCTCGAT
Three Types
• Insertion: One
nitrogen base is
inserted or
added to a DNA
strand
• Normal DNA:
TAGCGCTA
ATCGCGAT
• Mutated DNA:
TAGCGCTA
ATTCGCGAT
Three Types
3. Deletion: one
nitrogen base
is deleted
from the DNA
strand
• Normal DNA:
TAGCGCTA
ATCGCGAT
Mutated DNA:
TAGCGCTA
ATCGCAT
Substitution Examples
Normal DNA:
AAA ATG CTT
DNA with Mutation:
AAA ATG TTT
mRNA:
UUU UAC GAA
mRNA:
UUU UAC AAA
Amino Acid:
Phe-Tyr-Glu
Amino Acid:
Phe-Tyr-Lys
Create:
1. DNA strand with one base
inserted
2. DNA strand with one base deleted
How does this effect amino acid
sequence?
Chromosomal Mutations
• Deletion: loss of a piece of chromosome
Mutation Type 2 & 3
• Inversion: chromosomal segment breaks off,
flips around backward, and reattaches
• Translocation: piece of one chromosome
breaks off and reattaches to a
nonhomologous chromosome
Mutation Type #4
• Nondisjunction- chromosome fails to
separate from it homologue
Protein Synthesis
Transcription
DNA
• Double
stranded
• Deoxyribose
sugar
• Thymine
• Nucleus
vs. RNA
• Single
stranded
• Ribose sugar
• Uracil
• Anywhere
3 Types of RNA
• Messenger RNA (mRNA): Carries
information from DNA to
ribosome for________________.
protein synthesis
• Transfer RNA (tRNA): Transport
_________________.
amino acids
• Ribosomal RNA (rRNA): makes
up the _____________.
ribosomes
Part 1:Steps of Transcription
1. An enzyme
_________ attaches to a section of
DNA, separating the two strands.
2. The enzyme moves down the DNA,
building a strand of RNA that is
complementary to the DNA.
__________________
STOP code
3. The enzyme reads a ________
and the new strand of RNA is
completed and moves into the
cytoplasm
_______________.
Protein Synthesis
Translation
The genetic code
• The base sequence is read in
groups of ____________________________.
three adjacent nucleotides
• Each 3-nucleotide sequence is
codon
called a _________.
• Each codon encodes for a specific
stop
amino
acid a ______or
start ______signal.
____________or
Amino Acid
Anti-codon
Steps of Translation
ribosome
1. mRNA attaches to a ____________.
Amino acids floating in the
cytoplasm are transported to
tRNA
the ribosome by _______.
2. The first tRNA binds to the
start codon: AUG.
______
3. Another tRNA binds to the next
codon and carries the appropriate
peptide bond forms
amino acid. A __________________
between the two amino acids.
4. The first tRNA leaves and the
ribsome moves across the next
codon
__________.
5. Another tRNA binds to the codon
and attaches the corresponding
polypeptide
amino acid. The __________________
chain continues to grow.
6. Finally, the ribosome reads the
___________________,
and the
STOP codon
polypeptide falls off the ribosome.
http://www.wellesley.edu/Chemistry/chem227/nucleicfunction/translation/prtsynth.mov
Amino
acid
polypeptide
tRNA
ribosome
mRNA
The final step of protein
synthesis:
The polypeptide made at
the end of translation,
folds into the proper
shape
________, becoming a
protein
functional ________.
The central dogma of biology
DNA  RNA  protein