Lecture 4 Outline (Ch. 12 & 13)
I.
Cell Cycle
II.
Cell Spindle & Mitosis
A.
B.
Stages
Plants vs. Animals
III. Cell cycle controls
IV. Genetics Overview
V.
Cell Reproduction
VI. Karyotypes & Meiosis
A.
B.
Stages
Compare to mitosis
VII. Independent Assortment
VIII. Crossing-over/recombination
IX. Lecture Concepts
Cell cycle overview
-repeated
-regenerative
-inputs, outputs
Cell cycle phases
• cell cycle phases:
• G1 – first gap
• S – DNA synthesis
• G2 – second gap
• Interphase : G1, S, G2
• M – mitotic phase
mitosis & cytokinesis
• human cell – cycle ~24 hrs.
M < 1hr, S ~10-12 hrs.
Cell Cycle
Purpose of cell division?
two identical daughter cells
• Divide DNA - karyokinesis
• Divide cell
- cytokinesis
• Division to duplicate body cells:
mitosis; somatic cells
-development
-replacement
• Division to form sex cells: meiosis; gametes (sperm and egg)
DNA Terminology
• All organism’s genes = genome
Human genome ~ 30,000 genes
~ 3.2 billion nucleotides
• chromosomes – packaged DNA
• humans – 46 chromo, in 23 pairs
– diploid (2n)
• most chromosomes – two “arms” – with centromere in middle
DNA duplication
• DNA duplication
• each chromosome copied
- sister chromatids
- attached at centromere
• condense hugely
• chromosomes divided
equally to daughter cells
How are chromosomes
separated accurately?
Mitosis
• mitotic spindle
- microtubules (MT) & assoc. proteins
• two poles of spindle
- MT organized
- centrosome – centriole pair
• MT radiate from centrosomes
- astral MT
- spindle MT
- kinetochore MT
Stages of Mitosis
• Before mitosis:
• DNA duplicates
• centrosomes duplicate
• nucleus intact
Stages of Mitosis
• Prophase
• DNA condenses
• nucleoli gone
• spindle forming
Prophase
Stages of Mitosis
• Prometaphase
• nuclear membrane
breaks
• spindle attaches
• DNA condensation
Prophase
Prometaphase
Stages of Mitosis
• Metaphase
• centrosomes to ends
• kinetochores attach
• chromosomes line up
at metaphase plate
Prometaphase
Metaphase
Stages of Mitosis
• Anaphase
• sister chromatids
separate
• kinetochore MT
shorten
• spindle MT lengthen
Metaphase
Anaphase
Stages of Mitosis
• Telophase
• nuclear membrane
reforms
• chromosomes
decondense
Anaphase
Telophase
Stages of mitosis
• Cytokinesis
• begins during telophase
• completed after karyokinesis
- cell membrane pinches in
- cleavage furrow
- actin fibers at midline
Self-Check
1
Arrange mitosis
stages in order:
2
4
3
5
Mitosis in plant cells
• karyokinesis same in plant cells
• no centrioles, do have centrosomes
• cytokinesis different
Mitosis in plant cells
• cytokinesis different in plants:
• no cleavage furrow
• vesicles move on MT
• collect at midline – cell plate
• cell plate becomes cell wall
Mitosis in plant cells
• in dividing plant tissue – can find all stages of mitosis
Cell cycle controls
• transitions between phases?
• signals
• induce/promote
cycle progression
• molecular control
system
Cell cycle controls
• cycle proceeds until checkpoint
- critical stop vs. go choice
• three major checkpoints:
G 1, G 2, M
Cell cycle checkpoints
• G1 checkpoint critical
• G1 “go ahead” – cell
completes S, G2, & M
• G1 “no go” – cell exits cycle
- non-dividing phase - G0
• cells can return from G0 and reenter cycle
Cell cycle checkpoints
• checkpoints – signals
1. cyclin-dependent
kinase (Cdk)
2. cyclin
• Cdk - persists,
inactive w/out cyclin
• cyclin – degraded, accumulates
• Cdk + cyclin = MPF
• MPF – pass checkpoint
Cell cycle checkpoints
• G1 checkpoint – many Cdks & cyclins
• G2 checkpoint –
regulated by MPF
• M checkpoint – make sure all chromosomes
attached before division
Self-Check
stage
prophase
events Chromo
condense
Clues
Nuc intact
Chromo
copied
Fill in the chart above below each diagram with the stage of
the cell cycle and what is happening (events)
Self-Check
1. Draw and label the cell cycle in order – include first checkpoint
2. Draw a cell in G1 with 4 chromosomes; Draw a cell in
metaphase with 4 chromosomes
3. Start with G1 cell = 6 chromo; draw mitosis products
Genetics overview
• heredity
- all genes from parents
• variation
- your gene combination
• genetics
- study of heredity and heritable variation
• gene – unit of heredity
• locus – location along chromosome
Cellular reproduction
• asexual reproduction – mitotic division
– clone
– little variation
• sexual reproduction – two parents
– gametes
– unique combinations of
gene variations
Cellular reproduction
• gametes – haploid (1n)
– one chromosome set
• somatic cells – diploid (2n)
– two sets; two parents
• karyotype – view of 2n set
• homologous chromosomes
one from each parent
• autosomes vs. sex chromosomes
Karyotypes
• Chromosomes from
human female cell
Karyotypes
• Aligned by homologues
Meiosis - introduction
• cell preparing to undergo division:
maternal
paternal
• sister chromatids
• centromere
• non-sister
chromatids
• homologous
chromosomes
Meiosis – overall goal
• reduce # of chromo 2n
• two parts: meiosis I & II
• meiosis I – separate
homologues
• meiosis II – separate
sister chromatids
• input: one 2n cell
• output: four 1n cells
1n
Meiosis I
• interphase
-chromo
replicate
-centrosomes
replicate
• prophase I
• metaphase I
-condense
-metaphase
plate
-synapsis
-crossing
over
-tetrads
-homologues
attached to MT
• anaphase I
-homologues
separated
Meiosis I to Meiosis II
• telophase I & cytokinesis
• prophase II
-sister chromatids attached
-no DNA replication prior
-cell is haploid
-cells not identical
Meiosis II
• prophase II
• metaphase II
-sister
chromatids
metaphase
plate
• anaphase II
-MT attach to
each chromatid
-separate
• telophase II &
cytokinesis
-four 1N cells,
genetically
distinct
Self-Check
• When does chromosome duplication occur?
• What is separated during meiosis I?
• “
“
meiosis II?
• “
“
mitosis?
Self-Check
• How many chromosomes?
one chromosome
= chromatid
• single or duplicated?
tetrad
sister chromatids
non-sister
chromatids
Mitosis vs. Meiosis
• no
synapsis
• synapsis
2n
• separate
sister
chromatids
• separate
homologues
1n
2n
• separate
sister
chromatids
2n
1n 1n 1n 1n
Independent assortment
• random arrangement
of homologues = independent
assortment
• chance of getting paternal homologue: 50%
• humans =
23 pairs
# of mat./pat.
combinations?
223, or ~
8 million
maternal
paternal
Crossing-over
maternal
paternal
• prophase I - synapsis
• chromo align gene by gene
• crossing-over = swap
bits of homologous DNA
Life cycles
• meiosis creates haploid cells
• gametes (sperm or eggs)
• gametes fuse = fertilization
• create zygote, diploid
• Human diversity:
Independent assortment
Crossing-over
Random fertilization
Self-Check
stage
events
What
to
look
for?
Prophase I
Metaphase I
Anaphase I
Telophase
I
Prophase II
Metaphase
II
Anaphase
II
Telophase
II
Lecture 4 concepts
-
Draw a diagram of the cell cycle – what happens at each step?
-
Recognize, describe, and order division stages for mitosis
-
Define ‘chromosome’, ‘karyokinesis’, ‘cytokinesis’, ‘sister
chromatid’, ‘centromere’, ‘spindle’, ‘checkpoint’, ‘G0’
-
Know different types of spindle microtubules
-
Compare and contrast plant and animal cell division
-
Describe how cyclin and Cdk control checkpoint G2
-
Recognize, describe, and order division stages for meiosis
-
Define ‘heredity’, ‘variation’, ‘gene’, ‘locus’, ‘chromosome’,
‘gamete’, ‘somatic’, ‘homologue’, ‘genetics’, ‘synapsis’
-
Explain what a karyotype is and what it is used for
-
Compare and contrast asexual and sexual reproduction
-
Describe three BIG ways sexual reproduction provides genetic
variation
-
Write out a list of new terminology and provide descriptions