Download DNA/RNA

DNA and RNA
DNA: The Model of Heredity
12-2 Chromosomes and DNA Replication
Copyright Pearson Prentice Hall
Griffith and Transformation
Griffith and Transformation
In 1928, British scientist Fredrick Griffith was trying to learn
how certain types of bacteria caused pneumonia.
He isolated two different strains of pneumonia bacteria
from mice and grew them in his lab.
Copyright Pearson Prentice Hall
Griffith and Transformation
Griffith made two observations:
(1) The disease-causing strain of bacteria grew into
smooth colonies on culture plates.
(2) The harmless strain grew into colonies with rough
edges.
Copyright Pearson Prentice Hall
Griffith and Transformation
Griffith's Experiments
Griffith set up four
individual experiments.
Experiment 1: Mice
were injected with the
disease-causing strain
of bacteria. The mice
developed pneumonia
and died.
Copyright Pearson Prentice Hall
Griffith and Transformation
Experiment 2: Mice
were injected with the
harmless strain of
bacteria. These mice
didn’t get sick.
Copyright Pearson Prentice Hall
Griffith and Transformation
Experiment 3: Griffith
heated the diseasecausing bacteria. He
then injected the heatkilled bacteria into the
mice. The mice survived.
Copyright Pearson Prentice Hall
Griffith and Transformation
Experiment 4: Griffith
mixed his heat-killed,
disease-causing bacteria
with live, harmless
bacteria and injected the
mixture into the mice.
The mice developed
pneumonia and died.
Copyright Pearson Prentice Hall
Griffith and Transformation
Griffith concluded that
the heat-killed bacteria
passed their diseasecausing ability to the
harmless strain.
Heat-killed diseasecausing bacteria
(smooth colonies)
Harmless bacteria
(rough colonies)
Live diseasecausing bacteria
(smooth colonies)
Dies of pneumonia
Copyright Pearson Prentice Hall
Griffith and Transformation
Transformation
Griffith called this process transformation because one
strain of bacteria (the harmless strain) had changed
permanently into another (the disease-causing strain).
Griffith hypothesized that a factor must contain information
that could change harmless bacteria into disease-causing
ones.
Copyright Pearson Prentice Hall
Avery and DNA
Avery and DNA
Oswald Avery repeated Griffith’s work to determine
which molecule was most important for
transformation.
Avery and his colleagues made an extract from the heatkilled bacteria that they treated with enzymes.
Copyright Pearson Prentice Hall
Avery and DNA
The enzymes destroyed proteins, lipids,
carbohydrates, and other molecules, including
the nucleic acid RNA.
Transformation still occurred.
Copyright Pearson Prentice Hall
Avery and DNA
Avery and other scientists repeated the
experiment using enzymes that would break
down DNA.
When DNA was destroyed, transformation did
not occur. Therefore, they concluded that DNA
was the transforming factor.
Copyright Pearson Prentice Hall
Avery and DNA
Avery and other scientists discovered that the
nucleic acid DNA stores and transmits the genetic
information from one generation of an organism to
the next.
Copyright Pearson Prentice Hall
The Components and Structure of DNA
The Components and Structure of DNA
DNA is made up of nucleotides.
A nucleotide is a monomer of nucleic acids made up of:
• Deoxyribose – 5-carbon Sugar
• Phosphate Group
• Nitrogenous Base
Copyright Pearson Prentice Hall
The Components and Structure of DNA
There are four
kinds of bases in
in DNA:
•
•
•
•
adenine
guanine
cytosine
thymine
Copyright Pearson Prentice Hall
The Components and Structure of DNA
Chargaff's Rules
Erwin Chargaff discovered that:
– The percentages of guanine [G] and cytosine [C] bases are almost
equal in any sample of DNA.
– The percentages of adenine [A] and thymine [T] bases are almost
equal in any sample of DNA.
Copyright Pearson Prentice Hall
The Components and Structure of DNA
X-Ray Evidence
Rosalind Franklin used X-ray
diffraction to get information
about the structure of DNA.
She aimed an X-ray beam at
concentrated DNA samples
and recorded the scattering
pattern of the X-rays on film.
Copyright Pearson Prentice Hall
The Components and Structure of DNA
The Double Helix
Using clues from Franklin’s pattern, James Watson and
Francis Crick built a model that explained how DNA
carried information and could be copied.
Watson and Crick's model of DNA was a double helix,
in which two strands were wound around each other.
Copyright Pearson Prentice Hall
The Components and Structure of DNA
DNA Double Helix
Copyright Pearson Prentice Hall
The Components and Structure of DNA
Watson and Crick discovered that hydrogen
bonds can form only between certain base
pairs—adenine and thymine, and guanine and
cytosine.
This principle is called base pairing.
Copyright Pearson Prentice Hall
Chromosomes and DNA Replication
12-2 Chromosomes and DNA Replication
Copyright Pearson Prentice Hall
DNA and Chromosomes
DNA and Chromosomes
In prokaryotic cells, DNA is located in the cytoplasm.
Most prokaryotes have a single DNA molecule containing
nearly all of the cell’s genetic information.
Copyright Pearson Prentice Hall
DNA and Chromosomes
Chromosome
E. Coli Bacterium
Bases on the
Chromosomes
Copyright Pearson Prentice Hall
DNA and Chromosomes
Many eukaryotes have 1000 times the amount
of DNA as prokaryotes.
Eukaryotic DNA is located in the cell nucleus
inside chromosomes.
The number of chromosomes varies widely from
one species to the next.
Copyright Pearson Prentice Hall
DNA and Chromosomes
Chromosome Structure
Eukaryotic chromosomes contain DNA and protein,
tightly packed together to form chromatin.
Chromatin consists of DNA tightly coiled around proteins
called histones.
DNA and histone molecules form nucleosomes.
Nucleosomes pack together, forming a thick fiber.
Copyright Pearson Prentice Hall
DNA and Chromosomes
Eukaryotic Chromosome Structure
Chromosome
Nucleosome
DNA
double
helix
Coils
Supercoils
Histones
Copyright Pearson Prentice Hall
DNA Replication
DNA Replication
Each strand of the DNA double helix has all the
information needed to reconstruct the other half by the
mechanism of base pairing.
In most prokaryotes, DNA replication begins at a single
point and continues in two directions.
Copyright Pearson Prentice Hall
DNA Replication
In eukaryotic chromosomes, DNA replication
occurs at hundreds of places. Replication
proceeds in both directions until each
chromosome is completely copied.
The sites where separation and replication occur
are called replication forks.
Copyright Pearson Prentice Hall
DNA Replication
Duplicating DNA
Before a cell divides, it duplicates its DNA in a process
called replication.
Replication ensures that each resulting cell will have a
complete set of DNA.
Copyright Pearson Prentice Hall
DNA Replication
During DNA replication, the DNA molecule
separates into two strands, then produces two
new complementary strands following the rules of
base pairing. Each strand of the double helix of
DNA serves as a template for the new strand.
Copyright Pearson Prentice Hall
DNA Replication
New Strand
Original strand
Nitrogen Bases
Growth
Growth
Replication Fork
Replication Fork
DNA Polymerase
Copyright Pearson Prentice Hall
DNA Replication
How Replication Occurs
DNA replication is carried out by enzymes that “unzip” a
molecule of DNA.
Hydrogen bonds between base pairs are broken and the
two strands of DNA unwind.
Copyright Pearson Prentice Hall
DNA Replication
The principal enzyme involved in DNA
replication is DNA polymerase.
DNA polymerase joins individual nucleotides to
produce a DNA molecule and then “proofreads”
each new DNA strand.
Copyright Pearson Prentice Hall
RNA and
Protein Synthesis
12-3 RNA and Protein Synthesis
Copyright Pearson Prentice Hall
Genes are coded DNA instructions that control
the production of proteins.
Genetic messages can be decoded by copying
part of the nucleotide sequence from DNA into
RNA.
RNA contains coded information for making
proteins.
Copyright Pearson Prentice Hall
The Structure of RNA
The Structure of RNA
There are three main differences between RNA and DNA:
• The sugar in RNA is ribose instead of deoxyribose.
• RNA is generally single-stranded.
• RNA contains uracil in place of thymine.
Copyright Pearson Prentice Hall
Types of RNA
Types of RNA
There are three main types of RNA:
• messenger RNA
• ribosomal RNA
• transfer RNA
Copyright Pearson Prentice Hall
Messenger RNA (mRNA) carries copies of instructions
for assembling amino acids into proteins.
Copyright Pearson Prentice Hall
Ribosome
Ribosomal RNA
Ribosomes are made up of proteins and ribosomal
RNA (rRNA).
Copyright Pearson Prentice Hall
Amino acid
Types of RNA
Transfer RNA
During protein construction, transfer RNA (tRNA)
transfers each amino acid to the ribosome.
Copyright Pearson Prentice Hall
Protein Synthesis
DNA
molecule
DNA strand
(template)
5
3
TRANSCRIPTION
mRNA
5
3
Codon
TRANSLATION
Protein
Amino acid
Transcription
Transcription
DNA is copied in the form of RNA
This first process is called transcription.
The process begins at a section of DNA called a promoter.
Copyright Pearson Prentice Hall
Transcription
RNA
RNA polymerase
DNA
Copyright Pearson Prentice Hall
RNA Editing
RNA Editing
Some DNA within a gene is not needed to produce a
protein. These areas are called introns.
The DNA sequences that code for proteins are called exons.
Copyright Pearson Prentice Hall
The Genetic Code
The Genetic Code
The genetic code is the “language” of mRNA instructions.
The code is written using four “letters” (the bases: A, U,
C, and G).
Copyright Pearson Prentice Hall
The Genetic Code
A codon consists of three consecutive
nucleotides on mRNA that specify a particular
amino acid.
Copyright Pearson Prentice Hall
The Genetic Code
Copyright Pearson Prentice Hall
Translation
Translation
Translation is the decoding of an mRNA message into
a polypeptide chain (protein).
Translation takes place on ribosomes.
During translation, the cell uses information from
messenger RNA to produce proteins.
Nucleus
Copyright Pearson Prentice Hall
mRNA
The ribosome binds new tRNA molecules and
amino acids as it moves along the mRNA.
Phenylalanine
tRNA
Methionine
Ribosome
mRNA
Start codon
Copyright Pearson Prentice Hall
Lysine
Translation
Protein Synthesis
Lysine
tRNA
Translation direction
mRNA
Ribosome
Copyright Pearson Prentice Hall
Translation
The process continues until the ribosome reaches a stop
codon.
Polypeptide
Ribosome
tRNA
mRNA
Copyright Pearson Prentice Hall
Codon
Genes and Proteins
Codon Codon
DNA
Single strand of DNA
Codon Codon Codon
mRNA
mRNA
Protein
Alanine Arginine Leucine
Amino acids within
a polypeptide
Copyright Pearson Prentice Hall
Mutations
12-4 Mutations
Copyright Pearson Prentice Hall
Mutations
Mutations are changes in the genetic material.
Copyright Pearson Prentice Hall
Kinds of Mutations
Kinds of Mutations
Mutations that produce changes in a single gene are
known as gene mutations.
Mutations that produce changes in whole chromosomes
are known as chromosomal mutations.
Copyright Pearson Prentice Hall
Kinds of Mutations
Gene Mutations
Gene mutations involving a change in one or a few
nucleotides are known as point mutations because
they occur at a single point in the DNA sequence.
Point mutations include substitutions, insertions, and
deletions.
Copyright Pearson Prentice Hall
Kinds of Mutations
Substitutions
usually affect no
more than a single
amino acid.
Copyright Pearson Prentice Hall
Kinds of Mutations
The effects of insertions or deletions are more
dramatic.
The addition or deletion of a nucleotide causes a
shift in the grouping of codons.
Changes like these are called frameshift
mutations.
Copyright Pearson Prentice Hall
Kinds of Mutations
In an insertion, an
extra base is inserted
into a base sequence.
Copyright Pearson Prentice Hall
Kinds of Mutations
In a deletion, the loss of a single base is deleted
and the reading frame is shifted.
Copyright Pearson Prentice Hall
Kinds of Mutations
Chromosomal Mutations
Chromosomal mutations involve changes in the number
or structure of chromosomes.
Chromosomal mutations include deletions, duplications,
inversions, and translocations.
Copyright Pearson Prentice Hall
Kinds of Mutations
Deletions involve the loss of all or part of a
chromosome.
Copyright Pearson Prentice Hall
Kinds of Mutations
Duplications produce extra copies of parts of a
chromosome.
Copyright Pearson Prentice Hall
Kinds of Mutations
Inversions reverse the direction of parts of
chromosomes.
Copyright Pearson Prentice Hall
Kinds of Mutations
Translocations occurs when part of one chromosome
breaks off and attaches to another.
Copyright Pearson Prentice Hall
Significance of Mutations
Significance of Mutations
Many mutations have little or no effect on gene
expression.
Some mutations are the cause of genetic disorders.
Polyploidy is the condition in which an organism has
extra sets of chromosomes.
Copyright Pearson Prentice Hall