Introduction to
CELL BIOLOGY
Facilitator: Caswell Mavimbela
Module Overview
• Mineral elements and their roles
• Compounds required in human body and
their biological importance.
• Cell structure and function
• Cellular organelles and their functions
• Reproduction in cells
What is cell biology?
• Branch of life science which deals with the study on cells
in terms of structure, function and chemistry.
• Structure: how they are made from molecules
• Function: how individual cells cooperate to make an
organism as complex as a human being
• Chemistry: Interaction of different molecules in the
synthesis of complex molecules essential for cell
function.
Before we can fully understand how a healthy human body
functions, how it develops and ages, and what goes
wrong with it in disease, we need to understand the cells
of which it is made.
Why study cell biology?
• Modern medicine: diagnosis of
diseases by determination of
proportion of cells in blood, size and
shape, deformities.
• Agriculture: Development of new
strains of crops and livestock to
ensure food security.
• Food Science: Food processing into
consumer ready foods.
Historical perspective (task)
• Cell theory
• Antonio van Leeuwenhoek
Recent Advances in Cell Biology
• A possible cure of HIV with bone marrow
transplant. Doctors announced in Berlin that a
man who received a bone marrow transplant for
leukemia was now also free of his HIV infection.
He received bone marrow from a donor with
CCR5 gene delta 32 gene believed to be
resistant to HIV.
• Breakthrough windpipe transplant of Claudia
Castillo - tissue grown from Ms Castillo’s own
bone marrow stem cells, using them to fashion
the new bronchus – a branch of the windpipe
Introduction
• Cell: basic building unit of from which all living
organism are made and can function
independently.
• Some organism are single celled (bacteria and
protozoa) while others are multicellular
(mammals and trees).
• Cells are precursors of tissues and then organs.
• Cells can grow & divide; move; respond to
complicated instructions; measure time (they get
old and die); can go wrong and make the living
organisms sick etc
Chemistry of Life
• Living organisms rely on complex processes to perform
and regulate the internal functions that are necessary to
maintain life.
• The term to describe all the processes is homeostasis,
the ability of a living organism to maintain its structure
and function intact, separate from its environment.
• The maintenance of homeostasis requires a series of
chemical reactions and each step in each reaction
requires the presence of specific substances.
• Vitamins and mineral elements are among the necessary
substances – not all are produced internally.
Chemistry of Life
• Require mineral elements to sustain life
and perform their function
• Macroelements – required in quantities –
used as bulding materials of organic
compounds
• Microelements – required in small
quantities – have great and essential
contribution.
A lack of iodine in one’s diet can
cause swelling of the thyroid
gland resulting in a GOITER. The
condition is reversible if iodine
is taken. (Don’t worry, we iodize salt)
Iodine is used by thyroid cells to
make hormones (chemicals released by one
cell into the blood and bind to a receptor on another cell,
which is one way cells talk to each other).
96% of living organisms is made
of:
carbon (C)
oxygen (O)
hydrogen (H)
nitrogen (N)
Macroelements
• Calcium (Ca+)– abundant in body – structural component
of bones and function of nervous system.
• Phosphorus (P)– Ass. with Ca in bone – important in
energy metabolism.
• Potassium (K+) – Milk – electrolyte – involved in fluid
balance.
• Sodium (Na+)– Combine with K+- fluid balance
• Chloride (Cl ) – Production of HCl for digestion.
• Sulphur – involved in protein synthesis.
• Magnesium (Mg)– Suppress certain hormones and
reduces stress. Metabolize Na, K, and Ca
Microelements
• Iron (Fe) – essential in erythropoesis and oxygen transport.
• Copper (Cu) – Enzyme component involved in energy
production, strengthening of connective tissue and brain
neurotransmission
• Chromium (Cr) – insulin performance and cellular glucose
uptake.
• Zinc (Zn) – Wound healing, antibody production and immune
response.
• Manganese (Mn) – essential for enzyme for fertility and
growth
• Cobalt (Co) – Part of Vitamin B12
• Iodine (I) – Thyroid metabolism
• Selenium (Se) – Combined with Vit E – essential in antioxidant, support immune system by preventing disease and
stress.
Inorganic to organic molecules
• Carbon, hydrogen, oxygen and nitrogen (95% of body weight)
are common elements in livings things.
• Carbon can bond with other elements (C,H,O,N) to create
different organic molecules due to possession of 4 electrons
• Ability of C to bond with itself, produce carbon chain of
various lengths (50+ carbon atoms) and shapes.
• Carbon chains makes up skeleton of organic molecules
• Hydrocarbon chain composed of H & C are usually
hydrophobic and combination with functional group that
ionizes them render them hydrophilic.
• Functional groups and isomers (molecules with identical
molecular formula but different arrangement of atoms) bring
diversity to organic molecules.
• Organic molecules (sugars, fatty acids, amino acids and
nucleotides) are based on carbon chain backbone.
Some Classes of Organic Compounds by
Functional Group
Organic molecules
• Can be small and large
• Large organic molecules are called polymers and are
made up of small organic molecules called monomers.
• Simple single sugars are called monosaccharides
(glucose or fructose), two of those would be disaccharide
(sucrose) while many forming a long chain are called
polysaccharides (starch or glycogen).
• Fatty acids and glycerol form fats
• Amino acids join to form proteins
• Nucleotides are the subunits of nucleic acids (DNA and
RNA)
1. Carbohydrates
• Def: any of a large group of compounds in which
hydrogen and oxygen, in the proportions in
which they exist in water, are combined with
carbon.
• Most abundant organic molecules in nature,
produced by autotrophs during photosynthesis.
• General formula to represent them is (CH2O)n.
• They are classified as mono-, di- and
polysaccharides.
1.1. Monosaccharides
(MBChB 24/02/2009)
• Monosaccharides – simple sugars with a
carbon backbone (6 carbons)
• Example: glucose(6C - hexose), fructose
(6C)and ribose (5C – pentose).
• Glucose and fructose are isomers but
differ in structure and functional group.
There is aldehyde and ketone respectiely.
• Characteristics: clear, sweet taste,
crystalline, solid and water soluble.
TASK
Find out the structure of galactose
1.2. Disaccharides
• Formed from two monosaccharides during
dehydration synthesis reaction (condensation).
The reverse is known as hydrolysis. It is the
splitting of a large molecule into two or more
parts by addition of water.
• Glucose + fructose = sucrose (sugar cane)
• Glucose + galactose = lactose (milk)
• Glucose + glucose = maltose (in stomach)
monosaccharides
disaccharides
Task
• Learn all the structures of monosaccharide
and disaccharides and their respective
chemical reactions.
1.3. Polysaccharides
• Most common include starch, glycogen and
cellulose (contains chains of glucose molecule)
and chitin (contain modified glucose).
• Starch and glycogen – energy storage in plants
and animals respectively. Cellulose and chitin –
structural purposes.
• In humans – glucose is converted to glycogen by
liver and muscles. Between meals glycogen is
broken down to glucose to keep stable blood
glucose conc. Starch from plants is broken down
to maltose and then glucose in stomach
1.3.1. Starch
• Composed of hundred of glucose
molecules
• Made by plants to store energy for future
use.
• Easily hydrolyzed into glucose molecules
• Humans and other animals (herbivores)
utilizes this energy reserves of plants
1.3.2. Glycogen
• Made in animal cells by condensation or
dehydration synthesis.
• Made for purpose of short-term energy storage.
• Stored in liver and muscles
• Diabetes mellitus: insulin dependence (type2) –
inadequate or ineffective pancreatic insulin
production to metabolise glucose. Glucose
become abundant in blood causing
hyperglycemia.
presented by NM Mogale
1.3.3. Cellulose
• Structural compound found in cell walls of
plant cells.
• Provide rigidity in stems, leaves and roots.
• Indigestible by humans
• Dietary cellulose also called fiber or
roughage, useful in humans to prevents
constipation.
• In plant cells each cellulose fibril contains several microfibrils.
Each microfibril contains many polymers of glucose hydrogen –
bonded together.
1.3.4. Chitin
• Has an amino group attached to each
glucose molecule.
• Main component of arthropods
exoskeleton
• Indigestible by humans.
BIOLOGICAL IMPORTANCE OF CARBOHYDRATES
• Carbohydrates serve both essential structure and energy-storage functions:
1. As structural components in cells eg chitin in the exoskeleton; cellulose in
the cell walls of plants and many protists; in vertebrate animals, the cell
coatings of connective tissue contain carbohydrates
2. As main source of energy: sugar (glucose) as short-term ernergy source;
starch (plants) and glycogen (animals) as intermediate-term energy storage.
2. Lipids
• Insoluble in water – lacks polar group.
Soluble in chloroform, benzene and ether.
• Composed of H, C and carboxyl functional
group.
• Most important lipids are fats, oils,
phospholipids and steroids.
2.1. Fats and Oils
Fats
Oils
Made up fatty acids and glycerol
Made up of fatty acids and glycerol
Animal origin
Plant origin
Solid at room temp°C
Liquid at room temp°C
Contains saturated fatty acids – c-chain, no
double bond
Contains unsaturated fatty acids – c-chain,
has double bond.
Less healthy
More healthier
Functions: Insulation, cushioning and
energy storage.
Prevents freezing.
• Glycerol contains 3 hydroxyl group – polar and water soluble.
• Fat result in reaction between 3 fatty acid portions and 3 hydroxyl
group of glycerol. 3 water molecules are produced.
• Glycerol fatty acids ratio = 1: 3. Fats and oils can be referred to
as triglycerides
• Fats and oils are long-term energy storage in both plants and
animals and are richer than glucose and glycogen
Structure of fat (triglyceride)
2.2. Phospholipids
• Contains phosphate group and are derived from
fatty acids, glycerol, phosphoric acid and nitrogen
base.
• They are constructed much the same as neutral fats
but instead of 3 fatty acids, one is replaced with a
phosphate and nitrogen group (resulting in a polar
head and non-polar tail)
• Its properties implies that they can form a separation
between two solutions in terms of the interior and
exterior. In the presence of water, they arrange
themselves in a double layer.
• Function: form the lipid bilayer of plasma membrane
Structure of a phospholipid
/nitrogen
Steroids
• A type of lipid with 4 fused carbon ring backbone.
• Varies according to the functional group attached to the
rings.
• Steroids include sterols (e.g. cholesterol), bile acids and
important hormones.
• Cholesterol is a precursor of several other steroids (bile
acids and hormones)
• Component of cell membrane
• Used in the production of bile
• Necessary for Vitamin D synthesis
• Forms sheaths of some neurons.
• Excess of cholesterol is linked to atherosclerosis
(hardening of arteries) – leading to possible coronary
heart disease.
Steroids and Sterols
Figure 1 shows the basic ring system of a steroid, a carbon skeleton with four
rings. The addition of one or more alcohol groups (-OH), creates a sterol, in
Figure 2, a cholesterol molecule, and in Figure 3, oestradiol or estradiol, an
important female sex hormone.
Proteins
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Large organic compounds made up of amino acids.
There are about 20 amino acids commonly found in cells e.g. alanine,
valine, serine, cysteine and lysine to name a few.
Amino acids differ in the nature of the R group they contain. This R group
range from a single H to complex ring compound, with some R group being
polar and others not.
All amino acids contains 2 important functional groups ( carboxyl - COOH
and amino group – NH2). This makes them hydrophilic at normal body pH.
Amino acids combine to form peptides and polypeptides. The bond between
the amino acids is covalent bond called peptide.
Structural proteins - important in maintaining shape of cells or organisms.
Example: Collagen (make up bone, skim, tendon, and cartilage), Keratin
(hair, skin ,nails and feathers), Fibrinogen (blood plasma protein responsible
for blood clotting) and Actin and myosin (muscle contraction).
Globular or regulator proteins – responsible for cellular and body functions.
Example: Enzymes (catalysts), hormones (chemical messengers e.g.
insulin secreted by pancreas to regulate blood sugar conc.), antibodies
(immune response) and microtubules (has structural function and can
conduct substance from one side of the cell to the other.
Protein denature in response of pH and Temp.
Chemical structure of amino acids
Nucleic acids
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Monomers of nucleic acids are nucleotides.
Each nucleotide is composed of 3 molecular components i.e. phosphate, pentose
sugar and nitrogen containing base.
Nucleic acids are huge polymers of nucleotides with specific func in cells e.g. DNA
and RNA
DNA is a genetic material that stores info on its own replication and order amino acids
follows to make proteins.
RNA is an intermediary in protein synthesis and conveys info from DNA regarding
amino acids sequence in protein synthesis.
DNA has a sugar deoxyribose while RNA, ribose - differs by lack of oxygen in
deoxyribose.
There are types of nucleotides each having its own base.
Bases (purines: adenine and guanine) and pyrimidines (thymine and cytosil). In RNA
uracil replaces thymine
Nucleotides form linear molecule called 2 strand (looks like a ladder) with sides of
ladder made by phosphate and sugar unit and rungs made by complementary base
pairs
Bases appear in any order but (T) pairs with (A), (G) with (C) with hydrogen bonds=
complementary base pairs Overall structure of DNA form a bouble helix while RNA is a single strand
Structure of DNA molecule
DNA Molecule
The structure of a DNA molecule resembles a ladder formed of sugars and phosphates, and four
nucleotide bases: adenine (A), thymine (T), cytosine (C), and guanine (G). The coding information in the
DNA is given by the order of the nucleotide bases, and each gene possesses a unique sequence of base
pairs. Scientists use these base sequences to locate the position of genes on chromosomes and to
construct a map of the entire human genome.
TASK
Read about
• Watson and Crick and their contributions
• Craig Venter and his contributions
• Human Genome Project
• Purpose of genetic mapping
Cell Structure and Functions
Chapter II
Characteristics of cells
• They are structural and functional units of
tissues, organs and organisms
• Small with high surface area to allow
movement of nutrients in and out of the
cell.
• Capable of reproduction, leading to growth
and development of an organism
• Arise from pre-existing cells
Cells
• Smallest living unit
• Most are microscopic
Discovery of Cells
• Robert Hooke (mid-1600s)
– Observed sliver of cork
– Saw “row of empty boxes”
– Coined the term cell
Cell theory
• (1839)Theodor Schwann & Matthias Schleiden
“ all living things are made of cells”
• (50 yrs. later) Rudolf Virchow
“all cells come from cells”
Principles of Cell Theory
• All living things are made of cells
• Smallest living unit of structure and
function of all organisms is the cell
• All cells arise from preexisting cells
(this principle discarded the idea of
spontaneous generation)
Cell Size
Major types of cells
Major Cell Types
Prokaryote
“Lacks true nucleus
– nucleoid region –
not bound by membrane
Single celled organism
e.g. bacteria
Eukaryote
“have true nucleus bound by membrane”
Animal cell
Plant cell
Prokaryotic cells
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Cell wall – contains
peptidoglycans (aminodisaccharide).
Capsule – gelatinous slimy
layer
Flagellum in motile bacteria
contains flagellin protein
Pili or fimbriae –
attachement
Ribosome – coordinate
protein synthesis.
Nucleoid region – loop of
DNA molecule – no nuclear
envelope.
Eukaryotic Cell
Differences between Pro and
Eukaryotic cells
Prokaryotic
Eukaryotic
No true nucleus – nucleoid region.
Has true nucleus surrounded by nuclear
membrane
Smaller
Larger
Has outer surrounding capsule and cell wall No capsule and only cell wall in plant cells
Less complex
More complex
Cell wall contain peptidoglycans
Plant cell wall contain cellulose. No wall in
animal cell.
DNA forms a loop – single chromosome
DNA housed in chromatin
No compartmentalization
Highly organized (internally) due to
compartmentalization by organelles
Lack organelles
Have many organelles
Difference between animal and
plant cells
Animal
Plant
Lack chlorophyll
Contains cell wall –
cellulose
Have chlorophyll
Have centriole
Lacks centriole
Have a small vacuole
Have a large central
vacuole
Lacks cell wall
Cell structures and functions
Lecturer overview
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Cell membrane
Cell organelle
Mitosis
Meiosis
Plasma Membrane
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Fluid mosaic model
Proteins in plasma membrane
Cell to cell recognition
Crossing of plasma membrane
– Passive
• Diffusion
• Osmosis - tonicity
• Facilitated transport
– and active transport
• Active transport
• Bulk transport
– Endocytosis
– Exocytosis
» Phagocytosis and pinocytosis
Cellular junctions
– Adhesion
– Tight
– Gap
– Desmosomes
Cell membrane
• Also called plasmalemma, plasma membrane or
phospholipid bi-layer.
• Made up of phospholipids – forming a double
layer
• It is selectively permeable
• Very thin and measures about 7-10 micrometers
• Phospholipids molecules are fluid to allow
stretching responding to stress or movement of
cholesterol and proteins.
Phospholipid bilayer
Chromosomes
Genetics
Cell Cycle
Mitosis
Meiosis
Eukaryotic chromosomes contain DNA
and protein
The chromosomes carry the genetic
information
 When a cell divides, chromatin fibers are
very highly folded, and become visible in
the light microscope as chromosomes.
 During interphase (between divisions),
chromatin is more extended, a form used
for expression genetic information.
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DNA is organized into informational
units called genes
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Chromosomes contain hundreds to
thousands of genes
Cell Cycle
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The cell cycle is a sequence of cell
growth and division.
The cell cycle is the period from
the beginning of one division to the
beginning of the next.
The time it takes to complete one
cell cycle is the generation time.
• Cells divide when they reach a certain size
• Cell division involves mitosis and
cytokinesis.
• Mitosis involves division of the
chromosomes.
• Cytokinesis involves division of the
cytoplasm.
• Mitosis without cytokinesis results in
multinucleate cells.
• Eukaryotic cell cycle
– Beginning of one division to beginning of
next
– Stages in eukaryotic cell cycle
– Interphase
• First gap phase
• Synthesis phase
• Second gap phase
– M phase
• Mitosis
• Cytokinesis
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Chromosomes become duplicated
during interphase
Cells are very active during
interphase, synthesizing biological
molecules and growing the G1 (gap)
phase
The S (synthesis) phase is marked
by DNA replication
The G2 (gap) phase occurs between
the S phase and mitosis
• Despite differences between
prokaryotes and eukaryotes, there are
several common features in their cell
division processes.
– Replication of the DNA must occur.
– Segregation of the "original" and its
"replica" follow.
– Cytokinesis ends the cell division process.
• Whether the cell was eukaryotic or
prokaryotic, these basic events must
occur.
Hereditary material is passed on to
new cells by mitosis or meiosis
Cell division, growth, and
reproduction
Interphase
Mitosis
Cytokinesis
Meiosis
Cell division
• Chromosomal packaging of DNA allows
efficient distribution of genetic material
during cell division
• Life cycle requires two distinct types of cell
division processes: mitosis and meiosis
• Cell division: one cell becomes two cells
during an organism’s life cycle
Mitosis
• Mitosis is nuclear division plus cytokinesis, and
produces two identical daughter cells during the
following steps:
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Prophase
Metaphase
Anaphase
Telophase.
• Interphase is often included in discussions of
mitosis, but interphase is technically not part of
mitosis, but rather encompasses stages G1, S, and
G2 of the cell cycle.
Interphase
The cell is engaged in metabolic activity and
performing its prepare for mitosis (the next
four phases that lead up to and include nuclear
division). Chromosomes are not clearly
discerned in the nucleus, although a dark spot
called the nucleolus may be visible. The cell
may contain a pair of centrioles (or
microtubule organizing centers in plants) both
of which are organizational sites for
microtubules.
Prophase
 Chromatin in the nucleus begins to condense
and becomes visible in the light microscope as
chromosomes.
The nucleolus disappears.
Centrioles begin moving to opposite ends of the
cell and fibers extend from the centromeres.
Some fibers cross the cell to form the mitotic
spindle.
Prometaphase
The nuclear membrane dissolves, marking
the beginning of prometaphase.
Proteins attach to the centromeres creating
the kinetochores.
Microtubules attach at the kinetochores and
the chromosomes begin moving.
Metaphase
Spindle fibers line the chromosomes
along the middle of the cell
nucleus. This line is referred to as
the metaphase plate.
Polar microtubules extend from the
pole to the equator, and typically
overlap
Kinetochore microtubules extend
from the pole to the kinetochores
This organization helps to ensure
that in the next phase, when the
chromosomes are separated, each
new nucleus will receive one copy of
each chromosome.
Anaphase
The paired chromosomes separate at
the kinetochores and move to
opposite sides of the cell.
The chromosomes are pulled by the
kinetochore microtubules to the
poles and form a "V" shape
Motion results from a combination of
kinetochore movement along the
spindle microtubules and through the
physical interaction of polar
microtubules.
Telophase
Chromatids arrive at opposite poles of cell,
and new membranes form around the daughter
nuclei.
The chromosomes disperse and are no longer
visible under the light microscope.
The spindle fibers disperse, and cytokinesis
will start.
Cytokinesis
In animal cells, cytokinesis results when a fiber
ring composed of a protein called actin around the
center of the cell contracts pinching the cell into
two daughter cells, each with one nucleus.
In plant cells, synthesis of new cell wall between
two daughter cells rather than cleavage furrow in
cytoplasm
Interphase
Prophase
Prometaphase
Metaphase
Anaphase
Telophase
Cytokinesis
Animated GIF (203Kb)
Reproduction
• Asexual reproduction
• Sexual reproduction
Asexual Reproduction
• A form of duplication using only mitosis.
• Example, a new plant grows out of the root or
a shoot from an existing plant.
• Produces only genetically identical offspring
since all divisions are by mitosis.
Sexual reproduction
• Formation of new individual by a
combination of two haploid sex cells
(gametes).
• Fertilization- combination of genetic
information from two separate cells that
have one half the original genetic
information
• Gametes for fertilization usually come
from separate parents
1. Female- produces an egg
2. Male produces sperm
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Both gametes are haploid, with a single
set of chromosomes
The new individual is called a zygote, with
two sets of chromosomes (diploid).
Meiosis is a process to convert a diploid
cell to a haploid gamete, and cause a
change in the genetic information to
increase diversity in the offspring.
Chromosomes in a Diploid Cell
Summary of chromosome characteristics
• Diploid set for humans; 2n = 46
• Autosomes; homologous chromosomes, one
from each parent (humans = 22 sets of 2)
• Sex chromosomes (humans have 1 set)
1. Female-sex chromosomes are homologous
(XX)
2. Male-sex chromosomes are non-homologous
(XY)
Number of sets of
chromosomes in a cell
• Haploid (n)-- one set chromosomes
• Diploid (2n)-- two sets chromosomes
• Most plant and animal adults are
diploid (2n)
• Eggs and sperm are haploid (n)
• Most cells in the human body are
produced by mitosis. These are the
somatic (or vegetative) line cells.
• Cells that become gametes are referred
to as germ line cells. The vast majority
of cell divisions in the human body are
mitotic, with meiosis being restricted to
the gonads.
• Diploid cells
– Characteristic number of
chromosome pairs per cell
• Homologous chromosomes
• Similar in length, shape, other features,
and carry similar attributes
• Haploid cells
– Contain only one member of each
homologous chromosome pair
Meiosis
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Diploid cells undergo meiosis to form
haploid cells
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Meiosis potentially produces four
haploid cells
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Meiosis involves two separate divisions
• Two successive nuclear divisions occur,
Meiosis I (Reduction) and Meiosis II
(Division).
• Meiosis I reduces the ploidy level from 2n
to n (reduction) while Meiosis II divides
the remaining set of chromosomes in a
mitosis-like process (division).
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In meiosis, homologous chromosomes
are separated into different daughter
cells
Meiosis I and meiosis II each include
prophase, metaphase, anaphase, and
telophase
The First Division
Meiosis I
• Prophase I is one of the most important
stages of meiosis.
During this stage, many crucial events
occur.
In prophase I,
• The spindle appears.
• Nuclear envelopes disappear.
• The DNA of the chromosomes begin to twist and
condense, making the DNA visible to the
microscope.
• Each chromosome actively seeks out its
homologous pair (which also has a sister
chromatid).
• The two replicated homologous pairs find each
other and form a synapse. The structure formed
is referred to as a tetrad (four chromatids).
• The point at which the two non-sister chromatids
intertwine is called a chiasma. Sometimes a
process known as crossing over occurs at this
point.
• This is where two non-sister chromatids
exchange genetic material. This exchange does
not become evident, however, until the two
homologous pairs separate.
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Prophase I includes synapsis and crossing
over
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Homologous chromosomes pair and
undergo synapsis
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One member of a pair is the maternal
homologue, the other is the paternal
homologue
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Synapsis is the association of four
chromatids (two from each homologue)
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In metaphase I, the tetrads line up along the
equator.
Anaphase I results in the separation of
homologous pairs. Cells are haploid at this
point.
Telophase I results in a brief reappearance
of nuclear envelopes, and the spindle
disappears. The cell waits momentarily
during interkinesis.
Interkinesis separates meiosis I and II; no
DNA synthesis occurs
The Second Division
Meiosis II
• In prophase II, the spindle reappears, and the
nuclear membrane fragments.
• In metaphase II, the chromosomes align at the
equator.
• In anaphase II, sister chromatids separate.
• In telophase II, the nuclear envelopes reappear,
and four haploid cells are the result.
Interphase
Prophase I
Metaphase I
Telophase I
Anaphase I
Prophase II
Metaphase II
Anaphase II
Telophase II
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Germ line cells undergo gametogenesis
– Spermatogenesis produces sperm
– Oogenesis typically produces eggs, or a
single ovum and two or more polar bodies