Download Chapter 12-13 Notes

Lesson Overview
Identifying the Substance of Genes
Chapter 12 & 13 DNA and RNA
Lesson Overview
Identifying the Substance of Genes
Timeline of the Discovery of DNA DO NOT COPY
• 1928 Griffith
Transformation of one type of bacteria into another
• 1944 Avery
DNA is the molecule responsible for transformation and makes up genetic
material of cells.
• 1952 Hersey and Chase
Confirmed DNA is the molecule that makes up genetic material of cells.
• Chargaff’s Rule
In DNA from all species, adenine = thymine and cytosine = guanine.
• 1950’s Franklin
X-ray diffraction photograph of DNA
• 1953 Watson and Crick
build a 3D model of structure of DNA
Lesson Overview
Identifying the Substance of Genes
1952 Hershey and Chase
– Studied viruses called bacteriophages.
– Bacteriophage: virus that infects bacteria
– Marked viruses with radioactive P and S, mixed with bacteria and
tested for radioactivity. (Sulfur is part of protein and Phosphorus
is part of DNA)
WHY??
DNA doesn’t contain sulfur and proteins doesn’t contain
phosphorus
Lesson Overview
Identifying the Substance of Genes
The Role of DNA
Store: Information: DNA stores information for
genes that control patterns of development.
Copy: Before a cell divides, it must make a
complete copy of every one of its genes
Transmit: the genetic information in a cell.
Lesson Overview
Identifying the Substance of Genes
Nucleic Acids and Nucleotides (Review chapter 2.3)
Nucleic acids are long molecules found in the cell
nucleus.
Subunit: Nucleotides
Nucleotides are made of:
– Nitrogen base
– Deoxyribose sugar
– Phosphate group
Lesson Overview
Identifying the Substance of Genes
Nitrogenous Bases and Covalent Bonds
DNA has four kinds of nitrogenous bases:
adenine (A), guanine (G), cytosine (C), and
thymine (T).
Lesson Overview
Identifying the Substance of Genes
Chargaff’s Rules:
The percentages of adenine [A] = thymine [T]
and
The percentage of guanine [G] = cytosine [C].
Lesson Overview
Identifying the Substance of Genes
Franklin’s X-Rays – Photo 51
British scientist Rosalind Franklin used saw
DNA with x-ray
Lesson Overview
Identifying the Substance of Genes
The Work of Watson and Crick
Watson and Crick built a model
that explained the structure and
properties of DNA.
Lesson Overview
Identifying the Substance of Genes
Hydrogen Bonding
Strands of DNA are held
together by Hydrogen bonds
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].
Lesson Overview
Identifying the Substance of Genes
The Replication Process
Before a cell divides, it duplicates its DNA in a
copying process called replication.
Each strand of the double helix of DNA serves
as a template, or model, for the new strand.
Lesson Overview
Identifying the Substance of Genes
The Replication Process
The two strands of the double helix separate, or “unzip,”
allowing two replication forks to form.
As each new strand forms, new bases are added
following the rules of base pairing. (A T and C G)
Lesson Overview
Identifying the Substance of Genes
The Replication Process
Each DNA molecule resulting from replication
has one original strand and one new strand.
Lesson Overview
Identifying the Substance of Genes
The Role of Enzymes
DNA polymerase: joins nucleotides to produce
a new strand of DNA
-“proofreads” new DNA strand.
Lesson Overview
Identifying the Substance of Genes
Telomeres
The tips of chromosomes are known as
telomeres.
The ends of DNA molecules, located at the
telomeres, are particularly difficult to copy.
Over time, DNA may be lost from telomeres
each time a chromosome is replicated.
Telomerase:
1. adds short, repeated DNA sequences
to telomeres
2. lengthens the chromosomes
3. Reduces likelihood that gene
sequences will be lost during replication.
Lesson Overview
Identifying the Substance of Genes
Replication in Living Cells
**Replication always occurs before cell
division
Prokaryotes: have a single, circular DNA
molecule in the cytoplasm. Replication
starts from a single point and proceeds in
two directions until the entire chromosome
is copied.
Eukaryotes: have up to 1000 times more
DNA and nearly all of the DNA is found in
the nucleus. Replication starts in
hundreds of places.
RNA & Protein Synthesis
Chapter 13
13.1
DNA = book of instructions that tells which
proteins to make
The path from genes to proteins has two steps:
1.
Transcription—copying the DNA codes to make RNA
2.
Translation—using the codes to make proteins
Ribonucleic Acid (RNA)
•
•
Long chains of nucleotides made by transcription
Most RNA is used for protein synthesis
Nucleotide Structure
DNA v. RNA
DNA
Deoxyribose (one less
oxygen)
RNA
Ribose
Nitrogen Bases
Adenine
Thymine
Guanine
Cytosine
Adenine
Uracil
Guanine
Cytosine
Phosphate
Same in both
Number of
strands
Double strand
(base pairs)
Single strand
(single bases)
Size
100s of million base
pairs
100s - 1000s of bases
5 Carbon Sugar
Three Forms of RNA
1.
Messenger RNA (mRNA) carries
copies of the instructions for protein
synthesis from the nucleus to the
cytoplasm
2.
Transfer RNA (tRNA) transfers the
amino acids to the ribosomes in the
order specified by the mRNA
3.
Ribosomal RNA (rRNA) is part of
the structure of ribosomes (where
proteins are made)
Transcription
• DNA is read and a strand DNA
of RNA is created from it.
A
• Segments of DNA are
T
templates to produce
complementary RNA
molecules
G
C
RNA
U
A
C
G
Transcription
• RNA Polymerase: reads
DNA during transcription,
builds RNA
• Promoters: sequences of
DNA that show RNA
polymerase where to attach
(BINDING SITE).
RNA Editing
• Introns: part of first draft of
RNA that is cut out and
discarded.
• Exons: all other parts spliced
together to form the final
mRNA
13.2
Translation = Protein Synthesis
• mRNA (from transcription) is
then translated by the ribosome.
• tRNA brings the appropriate
amino acids that are sequenced
to create the protein.
Proteins
(review Ch 2 pages 48-49)
• Amino Acids (AA): about 20 different types;
each with identical amino group and a
carboxyl group and a unique side group
• Polypeptide: long chains of amino acids
formed when the amine of one AA binds with
the carboxyl of next AA; order of AA
determined by the mRNA code
The Genetic Code
• 4 letters: A, U, G, and C
• 64 possible 3 letter combinations from 4 letters (4 x 4 x 4 = 64)
• Codon: 3 letter code found in mRNA; one AA per codon (and
some AA have multiple codons)
• Anticodon: 3 letter code found in tRNA that carries AA and is
the complement of a codon
Reading codons (version 1)
Reading Codons version 2
Protein Synthesis Animation:
http://www.biostudio.com/demo_freeman_protein_synthesis.htm
The Big Picture
13.3
Mutations
• Inheritable changes in genetic information
• Causes:
Random Errors in replication
Stress
Physical Mutagens (x – ray, UV light)
Chemical Mutagens (pesticides, tobacco)
13.3
Types of Mutations
• 2 types of mutations:
1. Gene Mutations (point and frameshift)
2. Chromosomal Mutations
Point Mutations
• Change in a single nucleotide in DNA
• Substitutions
• Insertions
• Deletions
Chromosomal Mutations
• Change in number or structure
of chromosomes
• Deletion
• Duplication
• Inversion
• Translocation
Effects of Mutations
• None
Change has no effect on the AA inserted
• Harmful
Disrupts normal cell function
• Sickle Cell Anemia
• Hemophilia
• Cancer
• Beneficial
Change increases variation in the species and improves chance
of survival in changing environmental conditions
• Pesticide resistant mosquitoes
• Polyploidy plants
13.4
Prokaryote Gene Regulation
• Proteins bind to parts of DNA to turn on/off transcription
Eukaryotic Gene Regulation
• Much more complex than in prokaryotes
• Important to cell differentiation in multi-cellular organisms
• Influenced by the physical and chemical environment of the
cell (example frog metamorphosis)