Download DNA, RNA and Protein

PART 1 - DNA REPLICATION
PART 2 - TRANSCRIPTION AND
TRANSLATION
DNA
REPLICATION
THE EUKARYOTIC CELL CYCLE –
DNA REPLICATION HAS TO HAPPEN BEFORE THE CELL
CAN DIVIDE SO BOTH CELLS HAVE DNA.
THINK ABOUT IT
Before a cell divides, its DNA must
first be copied.
How might the double-helix
structure of DNA make that
possible?
If the sequence of one strand is
known, the other strand is known
A T C G G C T A T C G A
T A G C C G A T AG C T
DNA Replication
DNA Replication
The structure of DNA explains how it replicates
DNA “unzips” down the middle
Free floating nucleotides pair up with both sides of the
DNA molecule
A
T
C
G
A
T
A
G
C
T
Original
AT
TA
CG
GC
AT
A
T
C
G
A
T
A
G
C
T
AT
TA
CG
GC
AT
Exactly Copied DNA Strands
DNA Replication
This process produces
two exact DNA
molecules
(Chromosomes) that
are the same
DNA never leaves the
nucleus
The Role of Enzymes
• How does this happen??
• DNA replication is carried out by a series of
enzymes.
• They first “unzip” a molecule of DNA by
breaking the hydrogen bonds between base pairs.
The Role of Enzymes
•
•
- DNA Polymerase
- DNA polymerase is an enzyme that joins
individual nucleotides to produce a new strand of
DNA.
•
- DNA polymerase also “proofreads”
Replication in Living Cells
– How does DNA replication differ in prokaryotic
cells and eukaryotic cells?
– Replication in most prokaryotic cells starts from
a single point and proceeds in two directions until
the entire chromosome is copied.
Replication in Living Cells
– How does DNA replication differ in prokaryotic
cells and eukaryotic cells?
•
In eukaryotic cells, replication may begin at
dozens or even hundreds of places on the
DNA molecule, proceeding in both directions
until each chromosome is completely copied.
Lesson Overview
Identifying the Substance of Genes
Lesson Overview
Identifying the Substance of Genes
Transcription
And
Translation
DNA Works as a Code
Codon- a three nucleotide sequence that
codes for a single amino acid
With 4 different types of nucleotides in triplet
codes, 64 combinations are possible
a) 61 of the codons code for 20 amino acids
b) 3 codons signal a stop- Identifies the end of a
protein
The genetic code is exact. If a sequence of
DNA is known, the resulting amino acid chain
(protein) is known
Amino
Acid
DNA codons
Serine
TCT, TCC, TCA, TCG, AGT,
AGC
ATT, ATC, ATA
Tyrosine
TAT, TAC
Leucine
CTT, CTC, CTA, CTG, TTA,
TTG
Tryptophan
TGG
Valine
GTT, GTC, GTA, GTG
Glutamine
CAA, CAG
Phenylalan
ine
TTT, TTC
Asparagine
AAT, AAC
Methionine
ATG
Histidine
CAT, CAC
Cysteine
TGT, TGC
Glutamic
acid
GAA, GAG
GCT, GCC, GCA, GCG
Aspartic
acid
GAT, GAC
Isoleucine
Alanine
Glycine
Proline
Threonine
GGT, GGC, GGA, GGG
Lysine
AAA, AAG
CCT, CCC, CCA, CCG
Arginine
CGT, CGC, CGA, CGG, AGA,
AGG
ACT, ACC, ACA, ACG
Stop codons
TAA, TAG, TGA
If DNA never leaves the
nucleus, how can the
DNA message get to the
site of protein production,
the ribosome?
Answer:
The
DNA message is copied to
RNA during the process of
Transcription
How do
RNA and
DNA differ?
THE STRUCTURE OF RNA
1. RNA is single stranded
2. The sugar in RNA is Ribose,
not deoxyribose as in DNA
3. The DNA nucleotide thymine is
replaced by the RNA
nucleotide Uracil
Genetic Code with RNA Codons
RNA’S FUNCTIONS: TWO
TYPES, TWO JOBS
1. m-RNA (messenger RNA) delivers
the copied DNA from the nucleus
to the Ribosome- the site of
protein synthesis
2. t-RNA (transfer RNA) picks up
specific amino acids in the
cytoplasm and delivers them to the
ribosome
STEPS IN PROTEIN SYNTHESIS
1.
2.
3.
4.
5.
6.
7.
DNA molecule unzip where the desired gene is located
Free floating RNA nucleotides pair with the DNA
strand forming m-RNA (Transcription)
The m-RNA leaves the nucleus and goes to a ribosome
A specific t-RNA delivers a specific amino acid to the
ribosome (Translation)
The m-RNA codon matches with the t-RNA anticodon
bringing the amino acid into its proper place
When the next amino acid is in place, the two are joined
in a condensation reaction
The process is repeated until a stop code is read and a
complete protein is formed
MUTATION- CHANGE IN THE
GENETIC CODE
1. Gene Mutation or Point Mutation- a
nucleotide base is added, subtracted or
changed to produce a change in the amino
acid sequence of a protein
A change in a single base in the DNA strand will result in
a change in the m-RNA strand and the resulting protein
Normal Hemoglobin
DNA
RNA
GGA CTC CTC CCU GAG GAG
5
Amino Acids
6
7
Proline Glutamic Acid Glutamic Acid
Sickle Cell Hemoglobin
GGA CAC CTC CCU GUG GAG
Proline
Valine
Glutamic Acid
CHROMOSOME MUTATIONINVOLVES A CHANGE IN MANY
GENES
a) Deletion- part of a
chromosome is lost
b) Inversion- part
of a chromosome is
flipped around
c) Translocation- part
of a chromosome is
added to another
chromosome
Somatic & Germ Mutations
a) Somatic mutations: change that
occurs in body cells. Affects only the
individual. Ie. cancer
b) Germ Mutations- changed in the
genetic code of gametes that will affect the
individuals offspring
Mutagens- substances capable of
causing damage to DNA
Most mutations are harmful
FRAME SHIFT
MUTATIONS
A) An insertion or deletion that
results in the reading frame being
shifted.
B) All codons following the mutation
will be changed.
C) Example:
THE RED DOG ATE THE CAT
HER EDD OGA TET HEC AT