Download Chapter 04

Chapter 04
Information
• A living cell is
self-organizing
system
• A cell contains
information and
machinery for its
own assembly,
maintenance,
repairs, and
replication
Life Comes
From Life
• Life flows from
generation to
generation in
an unbroken
chain
• Sudden
spontaneous
generation is
impossible
Information in Living Things
• Life’s information is
encoded in genes
• Genes are decoded
by machinery that
manufactures parts
to make a living
organism
Information Needs
Difference to Be Useful
Genetic Discoveries
1860s – Mendel
• “Factors” determine inheritance
• Every trait is controlled by a pair of
“factors”
• Traits have “dominant” and “recessive”
forms
Dominant
and
recessive
traits in the
garden pea
studied by
Mendel
Genetic Discoveries
1890s
•
•
•
•
Chromosomes discovered
Suspected carriers of heredity
Exist in pairs
Double before cell division and are
shared between daughter cells
Cell Division
• The chromosomes in this dividing cell have
separated in a way that will provide a complete
set of hereditary material to each new daughter
cell.
Alters fig. 4.16
Human Karyotype
• Karyotype: array of chromosomes that
belong to an individual cell
• Human cells have 46 chromosomes
Genetic Discoveries
1903 – Sutton
• Trait-determining “factors” are located
on chromosome pairs
• One chromosome comes from the
mother’s egg, the other from the father’s
sperm
Genetic Discoveries
1905 – Wilson & Stevens
• Specific chromosome carries specific
hereditary property
• X chromosome determines sex of offspring
• Two X chromosomes in female cells, one X
chromosome in male cells
• All eggs get X chromosome
• Half of sperm get X chromosome, other half
get Y chromosome
Genetic Discoveries
1906
• Mendel’s ‘factors” termed “genes”
• Chromosomes are chains of linked
genes
• Many genes are inherited together
Genetic Discoveries
1908 - Morgan
• Farther apart genes are on a
chromosome, the less likely they are to
be inherited together
• Relative positions of genes along fruitfly
chromosome are mapped
Genetic Discoveries
1909 - Garrod
• Certain inheritable diseases result when
particular proteins fail to perform normal
functions
Genetic Discoveries
1927
Mutations
• Changes in genes
• Produce new genetic characteristics
and inherited diseases
• Necessary for evolution
• Can be produced with x-rays
Types of
Mutations
Mutations and the
Development of
Cancer Cells
One Gene Makes One Protein
One Gene Makes One Protein
Genetic Discoveries
1944 - Luria
Bacteria
• Subject to same genetic and
evolutionary forces as plants and
animals
• Reproduce rapidly
• Become main experimental subject of
molecular genetics
Cloning a Human Gene in a Bacterium
Cloning a Human Gene in a Bacterium continued
Genetic Discoveries
1944 - Avery
• Genes are made of deoxyribonucleic
acid (DNA)
DNA is Coiled Within Chromosomes
Nucleotide to Genome
• Nucleotide - smallest information unit
• Gene – string of nucleotides that
specifies a protein
• Chromosome – spooled-up string of
genes packaged in a single unit
• Genome – all of the chromosomes of a
single organism
Nucleotide to Genome
Nucleotides
• 5-carbon sugar deoxyribose (DNA) or
ribose (RNA)
• Phosphate
• One of four nitrogenous
bases: adenine (A),
guanine (G), cytosine (C),
thymine (T) (RNA uracil
(U) replaces thymine)
Nucleotides
and DNA
Nucleotides – DNA and RNA
Nitrogen-containing Bases
• Purines: double-ring compounds
• Pyrimidines: single-ring compounds
DNA
Deoxyribonucleic Acid
• Combinations of four nucleotides
linked in long chains
• Repeating phosphate-sugar parts
link together to form backbone
DNA Discoveries
1949 - Chargaff
• DNA from different organisms contain
different amounts of the four nucleotides
• Amount of A = T
• Amount of G = C
DNA Discoveries
1952 – Wilkins & Franklin
• Examined shape of DNA using
x-ray diffraction
• DNA exists in two or three
chains with bases stacked
near each other
DNA Discoveries
1953 – Watson & Crick
• Base pairing: A with T; G with C
• Sugar-phosphate forms double-helix
backbone
DNA – Base Pairs
• Bases of nucleotides
match up in pairs
• A pairs with T
• G pairs with C
DNA – Base Pairs
• DNA always exists
as a double chain –
one sequence of
nucleotides paired
with its
complementary
sequence
DNA – Base Pairs
• Weak bonds
hold base
pairs together
• Allows easy
separation of
chains for
replication
DNA
The Double Helix
• Resembles ladder twisted into a spiral
• Thin: easily packed into small places
• Double strand: protects inward-facing
nucleotide sequence; essential for
copying
The
Structure
of DNA
DNA Replication
• Before a cell
divides, DNA
must be
doubled
• Each daughter
cell receives a
copy
The Stages of Mitosis
Mitosis is the process of cell division that produces two identical
cells from an original parent cell
DNA Replication
Overview
• DNA separates
• Complementary
nucleotides are
linked along
separated strands
DNA Replication
• Initiator
protein guides
unzipper
protein
(helicase) to
correct
position on
DNA
DNA Replication
• Unzipper
separates
DNA strands,
breaking
weak bonds
between the
nucleotides
DNA Replication
• Builders
(polymerases)
assemble new DNA
strand by joining
nucleotides to their
matching
complements on the
exposed strands
DNA Replication
• Phosphate bond
energy from the
new nucleotides
is used to make
the new bonds
DNA Replication
• Top strand is built
continuously as
the builder follows
behind the
unzipper, but the
lower strand
builds in the
opposite direction
DNA Replication
• Lower builder
makes a loop
with the DNA
strand and
builds along
the bottom
half of it
DNA Replication
• Bottom new
strand is
assembled in
short lengths
which are
spliced
together by
the stitcher
(ligase)
DNA Replication
• Straighteners
(single-strand
DNA binding
proteins) keep
single strand
of DNA from
tangling
DNA Replication
• Untwister
(topoisomerase)
unwinds the DNA
double helix in
advance of the
unzipper
Overview of DNA Replication
Multiplying DNA Using PCR
Multiplying DNA Using PCR
DNA Fingerprinting
Using Gel Electrophoresis
Sequencing a Gene
Overview of DNA Replication
Repair Enzymes
• Erasers (Repair
Nuclease): find
poorly matched
or damaged
nucleotides and
cut them out
Repair Enzymes
• Builders
(Polymerase): fill
gaps using other
DNA strand as a
guide
Repair Enzymes
• Stitchers
(Ligase): uses
ATP to restore
continuity of
backbone of
repaired strand
Life is Orchestrated by Proteins
Proteins
• Combinations of 20
different amino acids
linked in long chains
• Function is determined
by amino acid
sequence
• Amino acid sequence
is determined by DNA
sequence
Amino Acids
Link Together
to Form a
Protein
(Polypeptide)
Transcription
• DNA is located in the nucleus
• DNA’s instructions must reach
ribosomes in cell’s cytoplasm to make
proteins
• Transcription: cell makes a disposable
copy of pertinent genes (messenger
RNA) and sends it to the protein
assembly site (ribosomes)
Sending Information from the Nucleus
Nucleus
• Contains DNA
• Nuclear
envelope:
double outer
membrane
• Nuclear pores:
passageways
for molecules
entering and
leaving nucleus
Link to Cell Structure
Messenger RNA
• Made in nucleus
• Moves through
nuclear pores to
cytoplasm
• Brings information
from DNA to
ribosomes to direct
synthesis of
proteins
Transcription
Making a Messenger
• The enzyme RNA
polymerase binds
to a gene on a
DNA strand (at the
promoter site) and
opens up the
double helix
Transcription
Making a Messenger
• RNA polymerase moves
along the exposed DNA
strand, adding
complementary RNA
nucleotides which form the
messenger
Transcription
Making a Messenger
• As the
messenger is
assembled, it
separates
from the DNA
template
strand
Transcription
Making a Messenger
• When the RNA
polymerase
arrives at stop
sequence at
end of gene,
the messenger
RNA strand is
released
DNA Packaging
• DNA packaged to ensure message will
get to next generation
• Examples: pollen, nuts, seeds, spores,
sperm, egg
• Often carry food to sustain early stages
of new life
• Contain machinery for DNA to get
foothold