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