Transcript C H E M I S T R Y

Chapter 2
An Introduction to
Genes and Genomes
Introduction to Molecular Biology
Prokaryotic Cell Structure
Prokaryotic Cell
Eukaryotic Cell
Eukaryotic Cell Structure
Eukaryotic Cell Structure
Animal Cell
Plant Cell
Let’s
in on a cell!
DNA Zoom Interactive
DNA Discovery
(visit DNAi.org)
 Miescher – identified a nuclear substance he called nuclein
 Griffith – performed the first transformation
 Avery, McCarty, and Macleod – identified Griffith’s transforming
factor as DNA
 Chargaff – proved that the percentage of the DNA bases adenine
always equaled thymine and guanine always equaled cytosine
 Wilkins, Franklin, Watson & Crick – demonstrated the structure of
DNA
Structure of DNA
• Deoxyribose Sugar
• Phosphate
• Nitrogen Base
Structure of DNA
Purines – double ring
Pyrimidines – single ring
Structure of DNA
Nucleic Acid Overview
Structure of DNA
DNA Replication
When DNA makes an exact copy of itself
DNA Replication
DNA Replication
The first step in DNA
replication is for
the enzyme,
helicase, to unzip
the double
stranded DNA
molucule.
DNA Replication
Proteins hold the two strands apart.
An RNA primer lays down on each strand of
DNA.
DNA Replication
 DNA polymerase extends the primer by adding
complementary nucleotides.
 DNA polymerase can only extend in the 5’ → 3’ direction
DNA Replication
 Leading strand follows helicase.
 Lagging strand must wait for replication fork to open and
therefore forms discontinous Okazaki fragments.
 Ligase seals the nicks in the DNA backbone between the
Okazaki fragments.
helicase
Let’s put it all together
Click on the animation below.
Select the button for the “whole picture”.
DNA Replication Animation
Transcription
Making an RNA copy from a DNA template
RNA polymerase
RNA Structure
Uracil instead of thymine
Ribose sugar instead of
deoxyribose sugar
Single stranded
Can leave the nucleus
RNA Structure
mRNA – RNA copy of DNA that carries genetic
information from the nucleus to the ribosomes
rRNA – makes up the ribosomes
tRNA – carries amino acids to ribosomes for
protein synthesis
Transcription
RNA polymerase binds to a promoter
region on double stranded DNA and
unzips the double helix.
Transcription
Free RNA nucleotides pair with the
complementary DNA of the template strand
Transcription
RNA is processed
 Introns are spliced out
 7 methyl guanosine cap
 Poly-A tail
Transcription
mRNA leaves the nucleus and travels to
the ribosomes in the cytoplasm
ribosome
nucleus
Let’s put it all together
Transcription Animation
Practice
Central Dogma of Molecular Biology
Animation
Click to see Video
Translation
Making protein from mRNA
Translation
Important Definitions
 A codon is composed of 3
RNA nucleotides
 Each codon codes for one
amino acid
 Protein does the work in a
cell
Translation
Translation
First Base
U
C
A
G
Third Base
Second Base
U
C
A
G
U
C
A
G
phenylalanine
serine
tyrosine
cysteine
phenylalanine
serine
tyrosine
cysteine
Leucine
serine
(stop)
(stop)
Leucine
serine
(stop)
tryptophan
U
C
A
G
leucine
proline
histidine
arginine
leucine
proline
histidine
arginine
leucine
proline
glutamine
arginine
leucine
proline
glutamine
arginine
U
C
A
G
isoleucine
threonine
asparagine
serine
isoleucine
threonine
asparagine
serine
isoleucine
threonine
lysine
arginine
met (start)
threonine
lysine
arginine
U
C
A
G
valine
alanine
apartic acid
glycine
valine
alanine
apartic acid
glycine
valine
alanine
glutamic acid
glycine
valine
alanine
glutamic acid
glycine
Translation
Translation
Translation
Translation
• Asparagine, Serine, Methionine
• Tryptophan, Glycine, Lysine
• Proline, Leucine, Serine
• Aspartic acid, Histidine, Threonine
Translation
Always begins at a start codon and ends at a
stop codon.
The region between the start and stop codons is
called the open reading frame (ORF)
Practice
Click on the animation to transcribe and
translate a gene.
Click to see animation
Translation Initiation
 mRNA attaches to the
small subunit of a
ribosome
 tRNA anticodon pairs
with mRNA start
codon
 Large ribosomal
subunit binds and
translation is initiated
amino acid
tRNA anticodon
Translation Elongation
 Anticodon of tRNA carrying next amino acid binds to
codon on mRNA
 A peptide bond joins the amino acids and the first tRNA
is released.
Translation Termination
 Amino acid chain continues until a stop codon is read.
The amino acid chain is released and all of the
translation machinery is recycled to translate another
protein.
Let’s put it all together
Click on the animation below
Translation Animation
Translation Video
Let’s put it all together
5’-GATCTGAATCGCTATGGC-3’
Coding:
Template: 3’-CTAGACTTAGCGATACCG-5’
mRNA:
mRNA 5’-GAUCUGAAUCGCUAUGGC-3’
tRNA:
CUAGACUUAGCGAUACCG
amino acid:
Asp,
Leu,
Asn,
Arg,
Tyr,
Gly
Control of Gene Expression
Control of Gene Expression
Control of Gene Expression
Prokaryotes cluster genes into operons that are
transcribed together to give a single mRNA
molecule.
Control of Gene Expression
Lac Operon
 Promoter region allows RNA polymerase to attach
and begin transcription.
 Operator region is in the middle of the promoter.
Control of Gene Expression
If a repressor protein is bound to the operator,
RNA polymerase cannot pass to transcribe the
genes.
Control of Gene Expression
When the inducer
(lactose) binds to the
repressor protein, it
changes shape and falls
off of the operator
region.
Now RNA polymerase
can pass and transcribe
the genes into mRNA.
Let’s put it all together
Click on the animation below.
Animation of lac operon
Video of lac operon
Mutations
Mutations are changes in the DNA
sequence.
Mutations can be inherited or acquired.
Mutations
Mutagens are agents that interact with
DNA to cause mutations.
Examples are chemicals and radiation.
Mutations
 Point mutation changes a single base
 Point mutations can be silent, meaning they code for the
same amino acid.
Mutations
Point mutations can also code for a structurally
similar amino acid.
Mutations
 Point mutations are not always harmless.
 If the mutation occurs on a critical amino acid in the active site of
the protein, it can be detrimental, as in the case of sickle cell
anemia.
Mutations
Frameshift mutations cause a shift in the
reading frame by adding or deleting nucleotides.
Mutations
An example of a deletion causing a premature
stop codon.