11.1 Genes are made of DNA
Griffith Experiment
Avery
Experiment
-Destroyed
proteins
-Mice still
died with
mix
Hershey Chase Experiement
• Virus- nucleic acid wrapped in
protein; needs host to reproduce
• Bacteriophage- virus that infects
bacteria
Hershey Chase Experiment
Question 1 & 2
1. Explain how experiments done by
Griffith, Avery & Hershey and
Chase supported that genes are made
of DNA? [4 points]
2. Identify the parts of DNA and how the
double helix is put together (bases)?
[4 points]
11.2 Nucleic acids store
information in their sequences of
chemical units
DNA into chromosomes
Nitrogenous Bases
DNA- structures
DNA Nucleotide
Rosalind Franklin
& Maurice Wilkins
1950’s photographs of the DNA
molecule using X-ray crystallography
which showed the shape to be a helix
Erwin Chargaff
• 1951, proved that the % of A = T
and % of G = C
Watson &Crick
• 1953, used data from
the other scientists and
built models to finally
figure out the exact
structure of DNA
• 1962 won the nobel
prize in Medicine
11.3 DNA replication is the
molecular mechanism of
inheritance
DNA
Replication
DNA Replication
• Enzymes are protein molecules that
catalyze chemical reactions in a cell –
usually any protein ending in “ase” is
an enzyme
• Helicase- unwinds DNA
• DNA Polymerase 3 () - Adds
complementary nucleotide
• DNA Polymerase 1 ()- Checks for
error
• Single strand bind proteins- help hold
open DNA
DNA Replication
• DNA primase- makes an initiation
(starting) site for replication
• RNA primer- short segment of
RNA where DNA replication starts
• DNA ligase- binds two nucleotides
together
• Topoisomerase (gyrase)- relaxes
and recoils helix
DNA Replication
11.4 A gene provides the
information for making a specific
protein
DNA
• Deoxyribose
sugar
• A,T,C,G
• Double strand
• Stays in Nucleus
• DNA
&
RNA
• Ribose sugar
• A,U,C,G
• Uracil pairs with
adenine
• Single strand
• Nucleus to cytoplasm
• Messenger (mRNA),
transfer (tRNA),
ribosomal (rRNA)
Types of RNA
• mRNA - Messenger RNA: Encodes amino
acid sequence of a polypeptide.
• tRNA - Transfer RNA: Brings amino acids
to ribosomes during translation.
• rRNA - Ribosomal RNA: With ribosomal
proteins, makes up the ribosomes, the
organelles that translate the mRNA.
DNA & RNA
Beadle and Tatum
• Beadle and Tatum discovered when
looking at mutant Neurospora crassa
(bread mold)
• Individual gene produces a specific
enzyme
• One gene - one polypeptide
(combinaiton of amino acids)
DNA to Protein
Table of
Codons
11.5 There are two main steps
from genes to proteins
Transcription: Base Pairing of
mRNA with DNA
RNA Transcription
Steps of Transcription
1. DNA double helix unwound and
separated by RNA polymerase
2. RNA polymerase adds RNA
nucleotides together, making a
single strand of mRNA which is
complementary to 1 strand of the
DNA
Steps of Transcription
3. mRNA is processed (modified) before
leaving the nucleus
a. introns (non coding regions) are cut
out of the mRNA
b. exons (coding regions) are “spliced”
together to form the
final mRNA product
4. Introns are cut out and exons are
spliced together to form the final
copy of messenger RNA (mRNA)
RNA editing
•
Most eukaryotic protein-coding genes contain segments called introns, which break up
the amino acid coding sequence into segments called exons.
The transcript of these genes is the pre-mRNA (precursor-mRNA).
The pre-mRNA is processed in the nucleus to remove the introns and splice the exons
together into a translatable mRNA. That mRNA exits the nucleus and is translated in the
cytoplasm.
Transfer RNA (tRNA)
Adding Amino
Acids to a
Polypeptide Chain
Initiation
Translation
Elongation
Translation
Termination
Translation
Steps of Translation
1. mRNA leaves the nucleus and is
transported to the ribosome where
translation takes place
2. Ribosome holds onto the mRNA, the
mRNA codon AUG is located in the P site
of the ribosome
3. tRNA carries an amino acid to the P site of
the ribosome
4. Another tRNA carries the next amino acid
to the A site of the ribosome
Steps of Translation
5. Two amino acids are joined together with a
peptide bond
6. tRNA in the P site leaves
7. Ribosome moves along the mRNA until the
next codon is located in the A site
(the tRNA which was located in the A site
is now in the P site and is holding the
peptide chain)
8. tRNA carries the next amino acid to the A
site
Steps of Translation
9. New amino acid is joined to the
peptide chain (the polypeptide is
made of 3 amino acids)
10. tRNA in the P site leaves
11. Process continues until a stop codon
appears in the A site of the ribosome
12. Polypeptide is now complete
Rules for translation
1. Codon is a three-base “word” that
codes for one amino acid
2. Determine the amino acid coded for
by an mRNA codon use the genetic
code
3. Genetic code is universal – all species
use the same genetic code, the same
20 amino acids are used in all living
organisms
Summary of Translation Process
11.6 Mutations can change the
meaning of genes
Point vs. Frameshift Mutations
Chromosome Mutations
How mutations affect genes
1. A mutation is any change in the nucleotide
sequence of DNA.
2.Two categories of mutations
a. Base substitutions (point)– replacement of one
nucleotide with another
i. This can change the protein or not change the
protein
b. Base insertions or base deletions (frameshift) – addition
of an extra nucleotide or subtracting a nucleotide
i. Have more effect on the protein than a substitution
What causes mutations?
1. Mistakes during DNA replication can
cause mutations
2. Mutagens – physical or chemical
agents that cause mutations
a. Physical mutagens – high energy radiation, Xrays, Ultraviolet light
b. Chemical mutagens – chemicals that are
similar to DNA bases and cause incorrect basepairing
Mutations Effects
Body Cells
• Cancers
Gametes
• Birth defects
• Genetic
disorders
Ch. 11 Test
• Vocabulary
• DNA & RNA structure
• Replication, transcription, translationcontent and problems
• Scientists & experiments involved
• Mutations & mutagens- types and
effects