Cells and Cell Division

Chapter 2

Inner Life of Cell

Cells are the Smallest Units of Life All Cells have: 1. DNA

2. Cell membrane 3. Ribosomes

E. coli - Prokaryote

Animal cell - Eukaryote

Cell Structure Reflects Function

Prokaryotic cells (Bacteria and Archaea) do not contain a nucleus or other membrane enclosed organelles.

Eukaryotic (animal, plant, fungus and protist) cells contain a nucleus and membrane-bound organelles.

Genetic disorders alter cellular structure or function.

Plasma membrane

Mitochondrion

Centriole

Vacuole Lysosome

Nuclear envelope Nucleolus

Chromatin Nuclear pore

Nucleus

Ribosomes

Golgi complex

Microtubule

Rough endoplasmic reticulum

Smooth endoplasmic reticulum

Cytoplasm

Fig. 2-1, p. 20

Overview: Cell Organelles Extracellular fluid

Carbohydrate chain

Lipid bilayer

Various membrane proteins

Intracellular fluid Channel

Phospholipid molecule

Cholesterol molecule

The Cell Membrane

ER lumen

Ribosomes

Rough ER

Smooth ER

The Endoplasmic Reticulum

Rough endoplasmic reticulum

Food vacuole Phagocytosis

Food

Smooth endoplasmic reticulum

Transport vesicles

Lysosome

Golgi apparatus

Cell Transport

Outer membrane

Inner membrane

Intermembrane space

Matrix

Electron-transport proteins

Cristae

Fig. 2-5, p. 23

The Mitochondrion

The Nucleus

Macromolecules in Cells Three Phases of the Cell Cycle

Each daughter cell starts interphase

G1 Interval of cell growth, before DNA replication (chromosomes unduplicated)

S Interval when DNA replication takes place (chromosomes duplicated)

Cytoplasmic division

G2 Interval following DNA replication; cell prepares to divide

INTERPHASE

Fig. 2-7, p. 25

One chromosome (unreplicated)

One chromosome (replicated)

sister chromatids

centromere Fig. 2-9, p. 28

(a) Cell at Interphase The cell duplicates its DNA, and prepares for nuclear division.

Mitosis

Early Prophase Late Prophase Transition to Metaphase

Mitosis

Cytokinesis

Metaphase Anaphase Telophase Interphase

Mitosis, cont.

Summary: Mitosis Cytokinesis Divides the Cytoplasm

!  Cytokinesis •  Cleavage furrow divides the cell in two •  Organelles are distributed to two daughter cells

Progeria

Rare genetic disease that leads to premature aging due to a mutation of a scaffolding protein in the nucleus.

Cell Cycle Control

Proteins called “checkpoint proteins” monitor progression through the cell cycle.

Figure 2.18

Syndactyly

Mitosis and Apoptosis Apoptosis

Programmed cell death is part of normal development

Figure 2.20

Pompe Disease (Lysosomal Storage Disease) Alpha glucosidase deficiency MEIOSIS

Cell Division to produce Gametes

Meiosis

!  Reduces the genetic material by half !  Why is this necessary?

from mother from father child

meiosis reduces genetic content

toomuch!

Homologous Chromosomes Pair in Meiosis

!  Carry the same genes !  Pair during Meiosis I !  Separate in the

formation of gametes !  One copy of each pair

is from the mother and one is from the father.

Figure 1.3

(a)  Prophase I (b) Metaphase I (c) Anaphase I (d) Telophase I

Meiosis I: The Reduction Division Meiosis II: The Equational Division

Interkinesis no DNA replication between the two nuclear divisions.

(e) Prophase II (haploid)

(f) Metaphase II (g) Anaphase II (h) Telophase II

Non-disjunction in Meiosis I or II can lead to a Trisomy or Monosomy Summary: Meiosis

Members of chromosome pair Sister

chromatids

Each chromosome pairs with its homologue

Paired homologues separate in meiosis I

Sister chromatids

separate and become

individual chromosomes in

meiosis II

Sister chromatids

Fig. 2-14, p. 33

Combinations possible

1 2 3

or

or

or

How many different chromosome combinations are possible in meiosis with independent assortment?

Recombination (crossing over)

•  Occurs in prophase of meiosis I

•  Homologous chromosomes exchange genes

•  Generates diversity

a

b c

d

e

f

AB

C

D

E

F

A

B

C

D

E

F

a

b c

d e

f

Figure 3.5

Recombination (2)

•  Exchange between homologs

•  Occurs in prophase I

AB

C

D

E

F

a

b c

d e

f

c

d e

f

C

D

E

F

Letters denote genes and case denotes alleles

Figure 3.5

Recombination (3)

• Creates chromosomes with new combinations of alleles for genes A to F

AB

C

D

E

F

a

b c

d e

f

c

d

e

f

A

B

a

b

C

D

E

F

Figure 3.5

Tetrads Chiasmata Synaptonemal complex Homologous recombination

Chiasmata

In prophase I, crossing over or recombination events create chiasmata.

Figure 3.5

Comparison Mitosis and Meiosis MITOSIS MEIOSIS

Diploid cell 2n = 4 MEIOSIS I Prophase Replicated chromosomes with sister chromatids

Prophase Homologous

chromosomes pair, crossing

over occurs

Chromosome replication

Chromosome replication

Unpaired chromosomes align at equator of cell

Metaphase Homologous pairs align at equator of cell

Metaphase I

Homologous chromosomes separate during anaphase I

Anaphase I Telophase I Cytokinesis Anaphase

Telophase Cytokinesis

Sister chromatids separate during anaphase

Haploid n = 2 Daughter cells MEIOSIS II

Sister chromatids

separate during

anaphase II 2n 2n n n n n Diploid daughter cells Haploid daughter cells

Spermatogenesis: Sperm Formation

Figure 3.7

Oogenesis Spermatogenesis

•  Stem cells in testes divide mitotically to produce spermatocytes

•  Spermatocytes divide by meiosis to produce four equal sized haploid spermatids which mature into four sperm

.

Figure 3.9

Oogenesis: Ovum Formation •  Cells of the ovary divide to form oocytes •  Oocytes divide by meiosis •  Unequal cytoplasmic division •  A discontinuous process

– At birth, oocytes are arrested in prophase I

– At ovulation, an oocyte continues to metaphase II

•  The four meiotic products produce a functional ovum and three polar bodies.

Comparing Spermatogenesis and Oogenesis