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