Download DNA Protein Synthesis Notes

DNA
Replication &
Protein
Synthesis
Rosalind Franklin
Rosalind Franklin
made a crucial
contribution to the
discovery of the
double helix
structure of DNA,
but some would
say she got a raw
deal.
In 1953, Watson and Crick were the
scientists that proposed and built a
model of DNA that we still use
today!
Erwin Chargaff
• Discovered a relationship between the
nitrogen bases.
–A=T
–C=G
Nucleic Acids- large molecule that
contain information for the cell
•DNA- Deoxyribonucleic acid
•RNA- Ribonucleic acid
Characteristics of DNA
•DNA is located in the nucleus
•Makes up genes in our chromosome
•Double stranded (like a twisted ladder)
called a double helix
Nitrogen
base
phosphate
Deoxyribose
Structure of DNA- the basic unit of DNA is a
nucleotide
Consisting of THREE parts:
1. Phosphate
2. Five carbon sugar- deoxyribose
3. Nitrogen base
The nitrogen bases occur in pairs:
A & T- Adenine & Thymine
G & C- Guanine & Cytosine
How does the DNA form a double helix?
•The nucleotides ( phosphate,
deoxyribose sugar, nitrogenous base)
join together
•The backbone or “sides of the ladder”
are made of phosphate and sugar
•The middle or “steps of the ladder”
are made of nitrogenous bases
•The nitrogen bases are held together
by hydrogen bonds
The order of the bases
along a strand of DNA
determines or “spells
out” the traits of an
organism. Each group of
3 nitrogen bases are
called a triplet. It spells
out a specific amino
acid.
Checkpoint
• Name 3 parts of a nucleotide.
– Phosphate, Sugar, Nitrogenous base
• What kind of sugar is in DNA?
– Deoxyribose
• Name the 4 base pairs in DNA; Which ones
bind together?
– Adenine & Thymine
– Cytosine & Guanine
DNA Replication- the process
by which DNA makes an EXACT
COPY of itself for the purpose
of Mitosis (cell division).
•Replication takes place in
the nucleus.
How DNA Replicates:
5 steps
1.Helicase unwinds and unzips the DNA
strand.
2.Primase primes the DNA for
replication.
3.DNA Polymerase adds nucleotides
DNA Nucleotides floating around the
nucleus line up along the separated DNA
strands.
How DNA Replicates:
5 steps
4. Ligase reforms the Hydrogen bonds
between the nucleotides.
5. The 2 strands are proofread
Two new DNA molecules are formed. They twist
to form two separate double helixes (one for each
nucleus!)
Leading strand 5’ to 3’ only – Follows helicase Continuous
Lagging strand – 3’ to 5’ - Okazaki fragments
created and later linked together by Ligase Discontinuous
Checkpoint
• What is Helicase’s job?
– Unzip DNA
• What is the difference between Leading and Lagging
strands?
– Leading is continuous
– Lagging has gaps and fills backwards
• What is an Okazaki Fragment?
– Fragments of DNA in Lagging strand
• What are the jobs of Primase and Ligase?
– Primase preps DNA for replication
– Ligase forms Hydrogen bonds between strands
Protein Synthesis
From DNA to Protein
Characteristics of RNA
*RNA is made of nucleotides with three parts
•Phosphate
•RIBOSE sugar
•Nitrogenous base
•RNA can leave the nucleus
•Single stranded
*Four nitrogen bases: Adenine, URACIL,
Guanine, and Cytosine
*The complementary base pairs:
•A & U- adenine & uracil
•G & C- guanine & cytosine
RNA
DNA
1. Ribose sugar
1. Deoxyribose sugar
2. Uracil (instead of thymine)
2. Thymine
3. Single stranded
3. Double stranded
4. Move in and out of nucleus
4. Does not leave the nucleus
3 types of RNA
• mRNA – Messenger RNA – takes message
from DNA out of the nucleus
• tRNA – Transfer RNA – Transfers the amino
acid to the Ribosome
• rRNA – Ribosomal RNA – helps to form
ribosome
Protein Synthesis
•Proteins are long chains of amino acids made
in cells. 20 amino acids make up all Proteins
•Proteins carry out the instructions that are
found in the genetic code.
Protein synthesis is
a two step process:
1.Transcription
2.Translation
Transcription- messenger RNA (mRNA) codons
are made from DNA template pattern. The mRNA
leaves the nucleus and enters the cytoplasm. (3
steps)
1. Initiation - Transcription begins when RNA
polymerases binds to the DNA, and
separates it into two strands. (TATA box)
2. Elongation - nucleotides are added to the 3’
end of the growing RNA molecule.
3. Termination -Transcription proceeds until
the RNA polymerase reaches a termination
site on the DNA (the most common stop
sequence is AATAAA). At this point, the
mRNA is released.
TATA Box
TATA box is a DNA
promoter sequence that
indicates where a
genetic sequence can
be read and decoded. It
specifies to other
molecules where
transcription begins. The
TATA box is named for
its conserved DNA
sequence, which is most
commonly TATAAA.
A
Intron - is any nucleotide sequence within
a gene that is removed by RNA splicing.
Remains in the nucleus
Exon - is any nucleotide sequence that
remains after introns have been removed
by RNA splicing. May exit the nucleus.
Codon- a 3 base sequence in
messenger RNA (mRNA) which is
code for a specific amino acid
using the mRNA Codon Chart.
This codon pairs with an
anticodon (mirror image) found in
transfer RNA (tRNA) at the
Ribosome.
Checkpoint
• Name the 3 types of RNA
– mRNA, tRNA, and rRNA
• Name the 3 steps in Transcription
– Initiation, elongation, and termination
• Name the 4 bases in RNA
– Adenine, Cytosine, Guanine, and Urasil
• In what type of RNA would find a codon?
– mRNA
• In what type of RNA would find an anticodon?
– tRNA
Translation- amino acids
which make up proteins are
assembled through the
direction of the mRNA and
the tRNA.
1.A tRNA anticodon pairs
with the mRNA codon.
The tRNA is carrying (or
transferring) an amino
acid.
2.A peptide bond forms
between each amino
acid and forms a protein.
Checkpoint
• Draw steps from DNA to Protein
– DNA
mRNA
Transcription
Protein
Translation
• Name the bond formed between the amino
acids.
– Peptide Bond
MUTATIONS
Genetic Changes
Mutations- mistakes…they happen! : (
• Repair enzymes travel up and
down the DNA looking for
problems. Sometimes they can be
repaired.
• If the mistake is not repaired, a
MUTATION occurs.
• Some mutations are helpful
(evolution), some are harmful
(cancer), and some make no
difference in the organism.
Point Mutations- a change in a single base pair of
DNA.
The cat ate the rat.
The car ate the rat.
The t was changed for r
Frameshift Mutations- a mutation that shifts the reading of codons
*Deletion- a single base is DELETED
The cat ate the rat
The ata tet her at.
The c was deleted
*Duplication- a single base is DUPLICATED
The cat ate the rat.
The eca tat eth era.
The e was duplicated
*Insertion- a single base INSERTED for another base
The cat ate the rat.
The cat aat eth era.
The a was inserted
Translocation
Mutations
Chromosome
mutations in which
chromosome
segments, and the
genes they contain,
change positions.
Translocations can
occur within a
chromosome
(intrachromosomal)
or between
chromosomes
(interchromosomal).
An inversion is
a chromosome rearra
ngement in which a
segment of a
chromosome is
reversed end to end.
An inversion occurs
when a single
chromosome
undergoes breakage
and rearrangement
within itself.
Silent mutations are DNA mutations that
do not significantly alter the phenotype of
the organism in which they occur. Silent
mutations can occur in non-coding
regions (outside of genes within introns), or
they may occur within exons. When they
occur within exons they either do not result
in a change to the amino acid sequence of
a protein, or result in the insertion of an
alternative amino acid with similar
properties to that of the original amino acid,
and in either case there is no significant
change in phenotype
A missense mutation is a
point mutation in which a single nucleotide
change results in a codon that codes for a
different amino acid.
A nonsense mutation is a
point mutation in a sequence of DNA that
results in a premature stop codon, or
a nonsense codon in the transcribed
mRNA, and in a truncated, incomplete, and
usually nonfunctional protein product.
A mutagen is a physical or chemical
agent that changes the genetic
material, usually DNA, of an organism
and thus increases the frequency of
mutations. As many mutations cause
cancer, mutagens are therefore also
likely to be carcinogens.
Checkpoint
• Type of mutation that has no effect on the
organism.
– Silent mutation
• Name the mutation that is a change in a single
base pair.
– Point mutation
• True or False: All mutations are harmful?
– False
• Name the 3 types of frameshift mutations
– Insertion, Deletion, Duplication