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Lesson Overview
12.1 Identifying the
Substance of Genes
Lesson Overview
Identifying the Substance of Genes
Griffith’s Experiments
Griffith isolated two different strains of the same bacterial
species.
Only one of the strains caused pneumonia.
Lesson Overview
Identifying the Substance of Genes
Griffith’s Experiments
When injecting mice with disease-causing bacteria, the mice
developed pneumonia and died.
When injecting mice with harmless bacteria, the mice stayed
healthy.
Lesson Overview
Identifying the Substance of Genes
Griffith’s Experiments
First, Griffith took the S strain, heated the cells to kill them,
and then injected the heat-killed bacteria into mice.
Mice survived, suggesting that the cause of pneumonia was
not a toxin from disease-causing bacteria.
Lesson Overview
Identifying the Substance of Genes
Griffith’s Experiments
In Griffith’s next experiment, mixed the heat-killed S-strain
with live, harmless R strain and injected the mixture into
mice.
The injected mice developed pneumonia, and died.
Lesson Overview
Identifying the Substance of Genes
Transformation
Process called transformation - one type of bacteria is changed
permanently into another.
Because the ability to cause disease was inherited by the
transformed bacteria, Griffith concluded that the transforming
factor had to be a gene.
Lesson Overview
Identifying the Substance of Genes
The Molecular Cause of Transformation
Avery extracted molecules from heat-killed bacteria and
destroyed proteins, lipids, carbohydrates, and RNA.
Transformation still occurred.
Lesson Overview
Identifying the Substance of Genes
The Molecular Cause of Transformation
Then destroyed DNA and transformation did not occur.
Therefore, DNA was the transforming factor.
This led to the discovery that DNA stores and transmits genetic
information.
Lesson Overview
Identifying the Substance of Genes
Bacteriophages
Bacteriophage - virus that infects bacteria
Lesson Overview
Identifying the Substance of Genes
The Hershey-Chase Experiment
Hershey and Chase studied a bacteriophage with a DNA core and a
protein coat.
Wanted to determine if the protein coat or the DNA core entered the
bacterial cell
Hershey and Chase grew viruses containing radioactive isotopes
of phosphorus-32 (P-32) and sulfur-35 (S-35)
Lesson Overview
Identifying the Substance of Genes
The Hershey-Chase Experiment
Bacteria contained phosphorus P-32 , the marker found in DNA.
Hershey and Chase concluded that the genetic material of the
bacteriophage was DNA, not protein.
Experiment confirmed Avery’s results - that DNA was the genetic
material found in genes.
Lesson Overview
Identifying the Substance of Genes
The Role of DNA
DNA can store, copy, and transmit genetic information
Lesson Overview
12.2 The Structure of DNA
Lesson Overview
Identifying the Substance of Genes
Nucleic Acids and Nucleotides
Located in the nucleus.
Made up of nucleotides, linked to form long chains.
Three components: a 5-carbon sugar called deoxyribose, a
phosphate group, and a nitrogenous base.
Lesson Overview
Identifying the Substance of Genes
Nucleic Acids and Nucleotides
Nucleotides joined by covalent bonds
DNA has four nitrogenous bases: adenine, guanine, cytosine,
and thymine, or AGCT
Lesson Overview
Identifying the Substance of Genes
Chargaff’s Rules
Chargaff discovered the
percentages of [A] and [T] bases
are almost equal in any sample of
DNA. The same thing is true for the
other two nucleotides, guanine [G]
and cytosine [C].
The observation that [A] = [T] and
[G] = [C] became known as one of
“Chargaff’s rules.”
Lesson Overview
Identifying the Substance of Genes
Franklin’s X-Rays
Rosalind Franklin used X-ray
diffraction that showed:
- DNA has 2 strands that are
twisted around each other.
- The nitrogen bases are near
the center.
Lesson Overview
Identifying the Substance of Genes
The Work of Watson and Crick
Franklin’s X-ray pattern enabled
Watson and Crick to build a
model of the specific structure
and properties of DNA.
Built three-dimensional model
of DNA in a double helix
Lesson Overview
Identifying the Substance of Genes
Antiparallel Strands
DNA strands are “antiparallel”— they run
in opposite directions.
Enables the nitrogenous bases to come
into contact at the center.
It also allows each strand to carry
nucleotides.
Lesson Overview
Identifying the Substance of Genes
Hydrogen Bonding
Hydrogen bonds form between certain
nitrogenous bases, holding the two
DNA strands together.
Hydrogen bonds are weak forces that
allow the two strands to separate.
Ability to separate is critical to DNA’s
functions.
Lesson Overview
Identifying the Substance of Genes
Base Pairing
Watson and Crick realized that
base pairing explained
Chargaff’s rule. It gave a
reason why [A] = [T] and [G] =
[C].
Fit between A–T and G–C
nucleotides called base
pairing.
EUKARYOTIC DNA REPLICATION
Step 1 – Helicase unzips the DNA molecule.
Step 2 – DNA Polymerase adds on complementary
nucleotides in a 5’ to 3’ direction.
Step 3 – The lagging strand continues to replicate in
fragments instead of continually like the leading strand.
Leading Strand
Lagging Strand
OKAZAKI FRAGMENTS
Step 4 – Since the fragments still aren’t joined, the enzyme
ligase joins the fragments.
Step 5 – As replication continues, the leading and lagging
strand twist back into their helical form.
TELOMERES
Are the tips of chromosomes that make it less likely
important genes will be lost with replication.
PROKARYOTIC DNA REPLICATION
Starts at a single point,
and proceeds in 2
directions until the
entire chromosome
is copied.
PROKARYOTIC VS. EUKARYOTIC
DNA Replication Process [3D Animation] – Biology / Medicine Animations HD
https://www.youtube.com/watch?v=27TxKoFU2Nw
Lesson Overview
Fermentation
Lesson Overview
13.1 RNA
Lesson Overview
Fermentation
The Role of RNA
First step in decoding genetic
instructions is to copy DNA into RNA.
RNA, like DNA, is a nucleic acid that
consists of a long chain of
nucleotides.
RNA uses the base sequence copied
from DNA to produce proteins.
Lesson Overview
Fermentation
Comparing RNA and DNA
Each nucleotide in both DNA and RNA is made up of a
5-carbon sugar, a phosphate group, and a nitrogenous
base.
Three important differences between RNA and DNA:
(1) Sugar in RNA is ribose
(2) RNA is single-stranded.
(3) RNA contains uracil (U) in place of thymine (T).
Lesson Overview
Fermentation
Comparing RNA and DNA
The cell uses DNA “master plan” to prepare RNA
“blueprints.”
DNA stays in the cell’s nucleus, while RNA goes to the
ribosomes.
Lesson Overview
Fermentation
Functions of RNA
RNA is like a disposable copy of a
segment of DNA, a working copy of a
single gene.
RNA controls the assembly of amino
acids into proteins.
Lesson Overview
Fermentation
Functions of RNA
Three main types of RNA:
messenger RNA, ribosomal RNA, and transfer RNA.
Lesson Overview
Fermentation
Messenger RNA
The RNA molecules that carry
copies of instructions to other
parts of the cell are known as
messenger RNA (mRNA)
Lesson Overview
Fermentation
Ribosomal RNA
Ribosomal RNA (rRNA) make up
ribosomes and assemble proteins.
Lesson Overview
Fermentation
Transfer RNA
Transfer RNA (tRNA) transfers
each amino acid to the ribosome
as specified by the mRNA to make
proteins.
Lesson Overview
Fermentation
Making RNA - Transcription
Transcription – DNA serves as templates to produce
complementary RNA molecules.
Lesson Overview
Fermentation
Transcription
In prokaryotes, RNA synthesis
and protein synthesis take
place in the cytoplasm.
In eukaryotes, RNA is produced
in the nucleus and moves to
the cytoplasm to produce
proteins.
Lesson Overview
Fermentation
Transcription
Requires RNA polymerase, which separates DNA strands, then
uses one strand of DNA as a template to assemble
complementary strand of RNA.
Lesson Overview
Fermentation
Promoters
RNA polymerase binds to
promoters - regions of DNA
with specific base sequences.
Promoters show RNA
polymerase where to begin
making RNA.
Similar signals cause
transcription to stop when a
new RNA molecule is
completed.
Lesson Overview
Fermentation
RNA Editing
Portions of RNA are cut out and stay
in the nucleus are called introns.
The remaining pieces, known as
exons, are spliced together to form
the final mRNA, which exits the
nucleus.
Lesson Overview
Ribosomes and Protein Synthesis
Lesson Overview
13.2 Ribosomes and
Protein Synthesis
Lesson Overview
Ribosomes and Protein Synthesis
The Genetic Code
First step in decoding genetic messages
is to transcribe DNA to RNA.
Transcribed information contains a code
for making proteins.
The genetic code is read three “letters”
at a time, so that each “word” is three
bases long and corresponds to a
single amino acid.
Lesson Overview
Ribosomes and Protein Synthesis
The Genetic Code
Proteins are made by joining amino acids together into long
chains, called polypeptides.
There are about 20 amino acids.
Lesson Overview
Ribosomes and Protein Synthesis
The Genetic Code
The amino acids and their order
determine the properties of proteins.
Sequence of amino acids affects the
shape of the protein, which determines
its function.
Lesson Overview
Ribosomes and Protein Synthesis
The Genetic Code
Each three-letter “word” in mRNA is known as a codon.
A codon consists of three consecutive bases that specify a single
amino acid.
Lesson Overview
Ribosomes and Protein Synthesis
Start and Stop Codons
The methionine codon AUG
serves as the “start” codon for
protein synthesis.
Following the start codon, mRNA
is read, three bases at a time,
until it reaches one of three
different “stop” codons, which
end translation.
Lesson Overview
Ribosomes and Protein Synthesis
Translation
The decoding of mRNA into amino acids
and eventually a protein is known as
translation.
Lesson Overview
Ribosomes and Protein Synthesis
Steps in Translation
mRNA is transcribed in the nucleus and then translated in the
cytoplasm.
Lesson Overview
Ribosomes and Protein Synthesis
Steps in Translation
Translation begins when a
ribosome attaches to mRNA.
As the ribosome reads each
codon of mRNA, it directs
tRNA to bring the amino acid
to the ribosome.
Lesson Overview
Ribosomes and Protein Synthesis
Steps in Translation
Each tRNA molecule carries
one amino acid.
In addition, each tRNA has three
unpaired bases, called the
anticodon — which is
complement to one mRNA
codon.
Lesson Overview
Ribosomes and Protein Synthesis
Steps in Translation
The ribosome forms a peptide bond
between the amino acids
At the same time, the bond holding
tRNA to its amino acid is broken.
Lesson Overview
Ribosomes and Protein Synthesis
Steps in Translation
The polypeptide chain grows until
the ribosome reaches a “stop”
codon.
When it reaches a stop codon, it
releases both the newly formed
polypeptide and the mRNA
molecule, completing translation.
Lesson Overview
Ribosomes and Protein Synthesis
The Roles of tRNA and rRNA in
Translation
rRNA holds ribosomal proteins in place and
locates the beginning of mRNA.
They may even join amino acids together.
Lesson Overview
Ribosomes and Protein Synthesis
The Molecular Basis of Heredity
Genes contain instructions for assembling proteins.
Lesson Overview
Ribosomes and Protein Synthesis
The Molecular Basis of Heredity
Gene expression - the way DNA, RNA, and proteins put genetic
information into action in living cells.
Lesson Overview
Ribosomes and Protein Synthesis
The Molecular Basis of Heredity
There is a near-universal nature in the genetic code.
Although some organisms show slight variations in the amino acids
assigned to particular codons, the code is always read three bases
at a time and in the same direction.
Despite their enormous diversity in form and function, living
organisms display remarkable unity at life’s most basic level, the
molecular biology of the gene.
Lesson Overview
Ribosomes and Protein Synthesis
Lesson Overview
13.3 Mutations
Lesson Overview
Ribosomes and Protein Synthesis
Types of Mutations
Now and then cells make mistakes in
copying their own DNA, inserting the wrong
base or even skipping a base as a strand is
put together.
These variations are called mutations
Mutations are heritable changes in genetic
information.
Lesson Overview
Ribosomes and Protein Synthesis
Types of Mutations
All mutations fall into two basic
categories:
Gene mutations - produce
changes in a single gene
Chromosomal mutations produce changes in whole
chromosomes.
Lesson Overview
Ribosomes and Protein Synthesis
Gene Mutations
Point mutations - involve
changes in one or a few
nucleotides.
If a gene in one cell is altered,
the alteration can be passed
on to every cell that develops
from the original one.
Lesson Overview
Ribosomes and Protein Synthesis
Gene Mutations
Point mutations include substitutions, insertions, and
deletions.
Lesson Overview
Ribosomes and Protein Synthesis
Substitutions
In a substitution, one base is changed to a different base.
Usually affect a single amino acid, and sometimes they have
no effect at all.
Lesson Overview
Ribosomes and Protein Synthesis
Insertions and Deletions
Insertions and deletions are point mutations in which one base
is inserted or removed.
Called frameshift mutations because they shift the “reading
frame” of the genetic message and can change the protein so
much that it won’t be functional.
Lesson Overview
Ribosomes and Protein Synthesis
Chromosomal Mutations
Chromosomal mutations involve changes in the number or
structure of chromosomes.
Can change the location of genes and the number of copies of
some genes.
Four types: deletion, duplication, inversion, and translocation.
Lesson Overview
Ribosomes and Protein Synthesis
Chromosomal Mutations
Deletion involves the loss of all or part of a chromosome.
Lesson Overview
Ribosomes and Protein Synthesis
Chromosomal Mutations
Duplication produces an extra copy of all or part of a
chromosome.
Lesson Overview
Ribosomes and Protein Synthesis
Chromosomal Mutations
Inversion reverses the direction of parts of a chromosome.
Lesson Overview
Ribosomes and Protein Synthesis
Chromosomal Mutations
Translocation occurs when part of one chromosome breaks off
and attaches to another.
Lesson Overview
Ribosomes and Protein Synthesis
Effects of Mutations
Genetic material can be altered by
natural or artificial means.
Resulting mutations may or may not
affect an organism, most do not.
Some mutations that affect individual
organisms can also affect a species or
even an entire ecosystem.
Lesson Overview
Ribosomes and Protein Synthesis
Effects of Mutations
Many mutations are produced by
errors in genetic processes.
During DNA replication, an
incorrect base is inserted roughly
once in every 10 million bases.
Small changes in genes can
accumulate over time.
Lesson Overview
Mutagens
Ribosomes and Protein Synthesis
Some mutations arise from
mutagens - chemical or physical
agents in the environment.
Chemical mutagens include
certain pesticides, plant alkaloids,
tobacco smoke, and
environmental pollutants.
Physical mutagens include forms
of electromagnetic radiation, such
as X-rays and UV light. Stress
can also be a factor.
Lesson Overview
Ribosomes and Protein Synthesis
Harmful Effects
The most harmful mutations dramatically change protein
structure or gene activity.
Example: Sickle Cell Disease
Lesson Overview
Ribosomes and Protein Synthesis
Beneficial Effects
Some mutations can be highly advantageous to an organism
or species.
Example: Pesticide Resistance and Polyploidy