Download Ch8 Cell Reproduction

Chromosome
• One DNA strand & attached proteins
• Condensed version of chromatin (long DNA strand)
• Duplicated in preparation for mitosis
one chromosome (unduplicated)
one chromosome (duplicated)
How much do you think a
chromosome is made up of
DNA/proteins?
• 40% DNA, 60% protein
Don’t forget what DNA looks like!
• Each chromosome consists of 2
identical parts called
sister chromatids.
• The point at which the sister
chromatids are connected is called
the centromere
• The kinetochore is the part of the
centromere that attaches to the
spindle fiber.
2 Types of chromosomes
• Autosomes –body chromosomes
• Sex chromosomes – determine the sex
X or Y
females XX
Males XY
What are 3
similarities
between
Homologues?
Hmm..
Is a chromosome in a DNA?
Or is DNA in a chromosome?
• DNA is in a chromosome
EUKARYOTIC
PROKARYOTIC
• FOUND?
• FOUND?
• LOOKS LIKE?
• LOOKS LIKE?
Chromosome Structure
DNA
one
Supercoil
=chromatin
1 strand of
double
helix
histone
Histones:
proteins that are entwined in
regularly arranged bead-like
groups along the DNA
• Keeps DNA strong so it
gives shape to
chromosomes
Nonhistones:
other proteins that control
certain parts of the DNA
Ex. DNA helicase –
Unzips 2 strands of DNA in
replication
C. Chromatin:
•
DNA strands are very tightly
wound into a supercoiled string,
which is coiled again, forming
chromatin.
• This allows for a great deal of
genetic information to be
compacted into a small area.
One, loooong strand of DNA
D. Genes:
• Segment of DNA that holds
instructions to make a
that will show a TRAIT
For example…
• The color of your hair is a:
• The building blocks that make up the
pigmentation of your hair are:
• The instructions on how to assemble
these proteins is found on a:
Comparison of Gene and Codon
GENE
1. Codes for a trait or
protein
2. Thousands of
different ones
3. Has many nucleotides
CODON
1. Codes for amino acids
4. Made of codons
5. Found in DNA
4. Codon is part of a gene
5. Found in mRNA
2. 64 possible codons
3. 3 nucleotide sequence
~23,000 genes
have been
identified in the
HUMAN GENOME
PROJECT
• Less on smaller x’s
• More on larger X’s
• SHOWS
CHROMOSOMES
PRESENT IN A CELL
Epigenetics – altering genes by
messing with OUTSIDE DNA stuff
like RNA or HISTONES!
Lots of DNA !
• Stretched out, the DNA from one human
body cell would be more than _______ !!!!!
There are over 6 billion nucleotides
• A single line of DNA from a salamander
cell would extend for ten meters
II. Chromosome Number
• DIPLOID
• HAPLOID
– 2n
–n
– Body cells
– Gametes (sperm or
egg cells)
– Humans 46
– Two of each type of
chromosome –
(homologous pairs)
– One of each
chromosome type
– Humans 23
Is an organism MORE complex if it
has MORE chromosomes???
• Nope!
• EVERY SPECIES HAS A SPECIFIC # OF
CHROMOSOMES
What is the animal
that has the highest #
of GENES ?
Microscopic WATER FLEA
(DAPHNIA) has 8000 more genes
than humans!
III. Human Chromosome Number
• Diploid chromosome number (2n) =
• Two sets of 23 chromosomes each
– One set from father
– One set from mother
• Mitosis produces cells with 46
chromosomes--two of each type
• Meiosis produces cells with 23
chromosomes – one of each type
Understanding Cell Division
• What instructions are necessary for inheritance?
• When you grow, how do you stay “you”?
• How is DNA passed into new cells made?
• How do you make “half” of a cell ready to make
a baby?
• How is DNA cut in half in a sex cell?
Roles of Mitosis
• Multicellular organisms
– Grow
– Replace Cells
• Unicellular organisms
– Asexual reproduction
Division Mechanisms
Eukaryotic organisms
– Mitosis
– Meiosis
Prokaryotic organisms
– _____________________________
(= mitosis)
3 easy steps to divide a
bacteria…err.. BINARY FISSION:
• 1. chromosomes make copies
• 2. cell grows til about 2x its size!
• 3. cell wall forms in between the
copied chromosomes and the cell
SPLiTS!
IV. Cell Cycle
• Cycle starts when a new cell forms
• During cycle, cell increases in mass and
duplicates its chromosomes
• Cycle ends when the new cell divides
A. Stages of Interphase
• G1 (GAP 1)
– Interval or gap after cell division – cell grows
• S (DNA SYNTHESIS)
– Time of DNA synthesis (replication)
• G2 (GAP 2)
– Interval or gap after DNA replicationprepares for cell division
The Cell Cycle
Fig. 8.4, p. 130
1. G1 Phase
• after cell division, daughter cells are
small and ATP is low
• rapid cell growth occurs
• certain enzymes used in DNA synthesis
are made
• cell carries out routine functions
• chromosomes are not visible – long thin
strands – chromatin
GDF 11 protein
(growth differentiation factor) might be key to
YOUTH bc it freezes cells at the G0 stage!
2. S Phase
• DNA replication; chromosomes – sister
chromatids form
3. G2 Phase
• preparation for mitosis
• energy level restored (ATP)
• Materials needed to manufacture mitotic
structures are made and stockpiled
• Increase in protein synthesis (enzymes)
4. Go Phase – (after G1) some cells do not
divide again (nerve cells)
Which phase is DNA copied??
• S phase
1. Control of the Cycle
• Once S begins, the cycle automatically
runs through G2 and mitosis
• The cycle has a built-in molecular brake in
G1
• Cancer involves a loss of control over the
cycle, malfunction of the “brakes”
Neoplasms – ignore Go stage
Masses of cells that have lost control over
how they grow and divide
Benign tumor
Malignant tumor (cancer)
Cancer Characteristics
• Plasma membrane and cytoplasm
altered
• Cells grow and divide abnormally
• Weakened capacity for adhesion; cells
can move to new tissues
• Lethal unless eradicated
2. Stopping the Cycle
• Some cells normally stop in interphase
– Neurons in human brain
• Adverse conditions can stop cycle
– Nutrient-deprived amoebas get stuck in
interphase
B. Mitosis
M Phase (Nucleus Divides)
• Period of nuclear division
• Usually followed by cytoplasmic division
• Four stages:
Prophase
Metaphase
Anaphase
Telophase
3. The Spindle Apparatus
• Consists of two distinct sets of
microtubules
– Each set extends from one of the cell poles
– Two sets overlap at spindle equator
• Moves chromosomes during mitosis
Spindle Apparatus
one spindle pole
one of the condensed
chromosomes
spindle equator
microtubules
organized
as a spindle
apparatus
one spindle pole
Stages of Mitosis
Prophase
Metaphase
Anaphase
Telophase
a) Mitosis
begins with Early Prophase
Duplicated
chromosomes begin
to condense and
are now visible
b) Late Prophase
• Centrioles move
away from each
other to opp. poles
(Plant cells have no centrioles, but spindle still forms)
• Nuclear envelope
starts to break up
c. Transition to Metaphase(pro-metaphase))
• Spindle microtubules
become attached to the
two sister chromatids
of each chromosome at
the kinetochore
• Pairs of chromatids
begin moving toward
equator
d) Metaphase (meet in the middle)
• All chromosomes are
lined up at the spindle
equator
• Chromosomes (sister
chromatids) are
maximally condensed
• Kinetochores split
this stage is used to
prepare KARYOTYPES
e) Anaphase (move apart)
• Sister chromatids of
each chromosome
are pulled apart
centromere first as
spindle fiber shorten
• Cell elongates
• Once separated
each chromatid is a
chromosome
f) Telophase
• Chromosomes decondense
(uncoil) until no longer
visible – chromatin
• Spindle fiber breaks apart
• Two nuclear membranes
form around each set of
unduplicated chromosomes
• Cell continues to elongate
g) Cytokinesis – Cell Dividing
• Two mechanisms
– Cell plate formation (plants) from within until a
barrier is formed between the two cells (cell wall)
– Cleavage (animals) cleavage furrow forms near
equator
1) Cell Plate Formation
Plant cells
2) Animal Cell Division
h) Results of Mitosis
• Two daughter nuclei
• Each with same
chromosome
number as parent
cell
• Chromosomes in
unduplicated form
i) Why is mitosis so IMPORTANT
for:
ii) UNICELLULAR ORGANISMS?
i)
It’s how they reproduce! (asexual)
iii) MULTICELLULAR
ORGANISMS?
–
–
–
–
keeps cells a small size (high SA: low V)
Allows each cell to differentiate (different
functions)
Fixes your boo-boos 
Makes you an ADULT!
Lesson 8.3 Meiosis
• How does the number of chromosomes in
an individual remain constant if sexual
reproduction occurs?
– Bc EGG & SPERM (GAMETES) cells have
half the # of chromosomes!
Asexual Reproduction
• Single parent produces offspring
• All offspring are genetically identical to one
another and to parent
Sexual Reproduction
• Involves
– Meiosis – reducing the chromosome
number from diploid to haploid to make
gametes
– Fertilization
• Produces DIVERSITY among offspring
Homologous Chromosomes
Carry Different Genes
• Cell has two sets of each chromosome
(2x23=46)
• One chromosome in each pair from
mother, other from father
brown
blue
Mom’s
Dad’s
Sexual Reproduction
will Shuffle Alleles
Meiosis: One Replication and
Two Divisions
Mitosis: One Replication and
One Division*
• Meiosis:
– Anaphase I – _________________________ separate
– Anaphase II – sister chromatids separate
• Mitosis:
– Anaphase - ___________________________ separate*
• Meiosis: 4 haploid nuclei form
• Mitosis: 2 diploid nuclei form*
Meiosis I
Meiosis II
B4 we start.. Lets go over some
vocab!
chromosome
Duplicated chromosome =
an “X” =
(common name – “chromosome”)
Synapsis – coming together
• When one “X” pairs up with his partner
“X”
Tetrad =
pair of Homologous chromosomes =
4 chromosomes =
2 “X’s”
Crossing-over
• When chromatid parts are exchanged with
their partner’s chromatid parts
Genetic recombination
• When crossing over mixes up the genes
Genetic recombination
• Changing
the
genetic
material
LAW OF INDEPENDENT
ASSORTMENT
• When traits are assorted (crossed over)
independently from each other
• It’s not the COLOR of your eyes changes
how TALL you are….
LAW OF SEGREGATION
• When homologous chromosomes (X’s)
randomly separate
• It’s not like all the mama chromosomes go
on one side of the cell and the papa
chromosomes go to the other….
Chiasmata
• Place where homologous chromosomes
touch and exchange genes
MEIOSIS I –
Interphase I
• Similar to mitosis
• where DNA replicates to form identical
chromatids which remain attached at their
centromere
• DNA condenses into
chromosomes
• Nuclear membrane
dissapears
• Centrioles start moving to
opposite sides
• Spindle fibers start
forming
• Each duplicated
chromosome pairs with
homologue –
SYNAPSIS occurs process that forms
TETRADS
• Homologues can swap
segments (non-sister
chromatids)
CROSSING OVER
Prophase I
Prophase I
•
•
•
•
DNA coils into chromosomes
Spindle fibers appear
Nucleus disappears
Chromosome pairs line up next to each other
• Chromatin condenses
into chromosomes
• Nuclear membrane
dissapears
• Centrioles start moving to
opposite sides
• Spindle fibers start
forming
• Each duplicated
chromosome pairs with
homologue –
SYNAPSIS occurs process that forms
TETRADS
• Homologues can swap
segments (non-sister
chromatids)
CROSSING OVER
Prophase I
Crossing Over
• In tetrad formation each
chromosome (duplicated)
becomes zippered to its
homologue
• All four chromatids are
closely aligned
• Non-sister chromosomes
exchange segments
Effect of Crossing Over
• After crossing over, each chromosome
contains both maternal and paternal
segments
• Creates new gene combinations in offspring
• Chiasma - chromosome with both parents’
DNA
Random Alignment
1
Possible
Chromosome
Combinations
or
or
or
2
3
Metaphase I
• Chromosomes
(tetrad) meet in the
middle
• The spindle fibers
are fully formed &
attached to tetrad
centromeres
• Random assortment
of chromosomes
(like blind dates )
Anaphase I
• *Homologous
chromosomes*
move apart
• The sister
chromatids remain
attached and move
together
Telophase I
• Cytokinesis occurs
• Nuclear membranes
reform
• Spindle fibers
disappear
• Each cell has a
HAPLOID # of
chromosomes that are
doubled (sister
chromatids)
For example…
Meiosis II  just like Mitosis
Prophase II
• Centrioles start to
move back to
opposite poles
• Nuclear membrane
starts to dissapear
• Spindle fibers start
forming
• NO replication of
chromosomes
• NO tetrad formation
Metaphase II
• *Sister chromatids*
meet in the middle
• Spindle fibers should
be attached to
centromeres by now
Anaphase II
• Sister chromatids
separate to become
independent
chromosomes
Telophase II
• Cytokinesis occurs
• Nuclear envelope
reforms around each set
of chromosomes
• Four haploid (n) cells –
each about ¼ the size of
original cell
Start with 4 chromosomes
first polar
body
(haploid)
oogonium
(diploid)
primary oocyte
(diploid)
secondary
oocyte
(haploid)
Growth
three polar
bodies
(haploid)
Meiosis I,
Cytoplasmic Division
ovum
(haploid)
Meiosis II,
Cytoplasmic Division
Oogenesis – making egg cells
Find the: ovum & polar bodies
spermatogonium
(diploid )
primary
spermatocyte
(diploid)
secondary
spermatocytes
(haploid)
spermatids
(haploid)
sperm (mature,
haploid male
gametes)
Spermatogenesis
Growth
Meiosis I,
Cytoplasmic Division
Meiosis II,
Cytoplasmic Division
cell differentiation,
sperm formation
Spermatogenesis – making sperm cells
Find the: spermatids & sperm
Fertilization
• Male and female gametes unite and nuclei fuse
• Fusion of two haploid nuclei  diploid nucleus
• 2 gametes coming together is random 
• More Independent Assortment!
– Adds to variation among offspring
When are 3 EVENTS that MIX
up the genes so each kid is
slightly different?!
• 1. Crossing over during prophase I
• 2. Random alignment of “X”
chromosomes at metaphase I
• 3. which sperm gets to which egg
released that month at fertilization
Prophase I
ProphaseII
Metaphase I
Metaphase II
Anaphase I
Anaphase II
Telophase I
Telophase II
MITOSIS
Sister
chromatids
line up
vs
MEIOSIS
Homologous
chromosomes
line up
Mitosis & Meiosis Compared
Mitosis
Meiosis
• 1 Division
• Makes 2 diploid cells
• Sister chromatids split
• 2 Divisions
• Makes 4 haploid cells
• Homologous
chromosomes split
• synapsis
• No pairing of
chromosomes
Mitosis & Meiosis Compared
Mitosis
• Functions
– Asexual reproduction
– Growth, repair
• Occurs in
somatic (body) cells
• Produces clones
(genetically identical)
Meiosis
• Function
– Sexual reproduction
• Occurs in germ (sex
cell-making) cells
• Produces variable
offspring (genetic
recombination)