Chapter-6Cell Cycle and DivisionCell Divisio.docx

Chapter-6
Cell Cycle and Division
Cell Division
Cells reproduce by cell division, in which a parent cell normally
gives rise to two daughter cells
Each daughter cell receives a complete set of hereditary
information (DNA) from the parent cell and about half its
cytoplasm
The hereditary information DNA is usually identical with that
of the parent cell

The cell division of eukaryotic cells by which organisms grow
or increase in number is called mitotic cell division
After cell division, the daughter cells may differentiate,
becoming specialized for specific functions
The repeating pattern of divide, grow, and differentiate, then
divide again is called the cell cycle
Most multicellular organisms have three categories of cells
1. stem cells
2. Other cells capable of dividing
3. Permanently differentiated cells

1.Stem cells :
- have two important characteristics: self-renewal, and the
ability to differentiate into a variety of cell types
-Stem cells self-renew because they retain the ability to divide,
perhaps for the entire life of the organism
-Some stem cells in early embryos can produce any of the
specialized cell types of the entire body

2. Other cells capable of dividing
-Some cells other than stem cells are capable of continuing
to divide, but typically differentiate into only one or two
different cell types
-Dividing liver cells, for example, can only become more liver
cells
-Permanently differentiated cells differentiate and never
divide again
-For example, most heart and brain cells cannot divide
CELL CYCLE
Both prokaryotic and eukaryotic cells have cell cycles that
include growth, metabolic activity, DNA replication, and cell
division
However, they have major structural and functional differences

Eukaryotic chromosome
Eukaryotic chromosomes are separated from the cytoplasm by a
membrane-bound nucleus
Eukaryotic cells always have multiple chromosomes
Eukaryotic chromosomes are longer and have more DNA than
prokaryotic chromosomes (human chromosomes are 10 to 80
times longer and have 10 to 50 times more DNA)
Genes
Genes are segments of the DNA of a chromosome
Genes are sequences of DNA from hundreds to thousands of
nucleotides long

Each gene occupies a specific place, or locus (plural, loci) on
the chromosome
Two important parts of chromosome
Two telomeres
One centromere
It temporarily holds two daughter DNA double helices together
after DNA replication
It is the attachment site for microtubules that move the
chromosomes during cell division
Homologous

11
Chromosomes that contain the same genes are called
homologous chromosomes, or homologues
Cells with pairs of homologous chromosomes are called diploid,
which means “double”
Cells with half the number of chromosomes are called haploid
Human Chromosomes
A typical human cell has 23 pairs of chromosomes, for a total of
46
Twenty-two out of 23 pairs are called autosomes

The twenty-third pair are called sex chromosomes and are
different in the male and the female
The female has two X chromosomes that usually look similar
The male has an X and a Y chromosome that appear very
different
However, in a male, the X and Y chromosomes behave as a pair
during meiotic cell division

Eukaryotic Cell Cycle
The eukaryotic cell cycle consists of interphase and cell
division
Interphase is a time for acquisition of nutrients, growth, and
chromosome duplication
During cell division, one copy of every chromosome and half of
the cytoplasm and organelles are parceled out into the two
daughter cells
Most eukaryotic cells spend the majority of their time in
interphase
Interphase is divided into three phases
G1 (growth phase 1):
--cell acquires nutrients
--It grows in size
--It specializes or differentiates

--It decides whether to divide
S (synthesis phase) is characterized by DNA synthesis, during
which every chromosome is replicated
G2 (growth phase 2) includes completion of cell growth, protein
synthesis for division and preparation for division of the cell
into daughter cells
Eukaryotic Cell Cycle

Types of Cell division
There are two types of cell division in eukaryotic cells
Mitotic cell division (mitosis)
Meiotic cell division (meiosis)/reduction division
Over view of mitosis
Prior to cell division, the DNA is replicated
At the end of DNA replication, a duplicated chromosome
consists of two identical DNA double helices, called sister
chromatids, which are attached to each other at the centromere
During mitotic cell division, the two sister chromatids separate,
each becoming an independent chromosome that is delivered to
one of the two daughter cells

Mitotic cell division involves two steps
During mitosis (nuclear division), the nucleus of the cell and
the chromosomes divide
Each daughter nucleus receives one copy of each of the
replicated chromosomes of the parent cell
During cytokinesis (cytoplasmic division), the cytoplasm is
divided roughly equally between the two daughter cells, and one
daughter nucleus enters each of the daughter cells

Mitosis consists of four phases followed by cytokinesis
Prophase
Metaphase
Anaphase
Telophase
Cytokinesis
Three major events occur in prophase

1. Duplicated chromosomes condense and the nucleolus begins
to disappear
2. Spindle microtubules form from centrioles and move toward
the nucleus, at the same time nuclear envelop disintegrates,
releasing the duplicated chromosome.
3.Chromosomes are captured by the spindle fiber. Each
chromatid is attached to a microtubule from opposite pole
PROPHASE

Metaphase
microtubule from one pole that is attached to a chromatid’s
centromere complex lengthens or shortens, as necessary, to
draw the chromosome to the cell’s equator, in a line
perpendicular to the spindle….creating a metaphase plate
During mitotic anaphase, daughter chromosomes (formerly
sister chromatids) are drawn to opposite poles
Sister chromatids separate during anaphase into daughter
chromosomes
chromatids are pulled apart along the microtubules and toward
opposite poles

Clusters of chromosomes that gather at each pole contain one
copy of every chromosome
Mitotic stages of animal cell

Telophase is the end stage of mitotic cell division
The spindle microtubules disintegrate
A nuclear membrane forms around each group of chromosomes
at the pole
Chromosomes unwind (decondense) and revert to their extended
state
The nucleoli (which disappeared in prophase) reappear
Cytokinesis in animal cells

Microfilaments attached to the plasma membrane form a ring
around the equator of a cell
The ring contracts and constricts the cell’s equator
Eventually, contraction of the ring pinches off the membrane,
forming two daughter cells, each with a nucleus identical with
the other
Following cytokinesis, animal cells enter G1 of interphase, thus
completing the cell cycle
Cytokinesis in plant cells
Stiff plant cell walls prevent the “pinching off” of cytokinesis

seen in animal cells, which only have a plasma membrane
Instead, carbohydrate-filled vesicles assemble along the cell’s
equator, between the daughter nuclei
The vesicles fuse into a continuous flattened sac, surrounded by
plasma membrane and filled with sticky carbohydrates
This is called a cell plate
The plasma membranes of the plate fuse with the plasma
membrane of the cell, forming two cells, with the carbohydrate
in between becoming part of the cell wall
As in animals, plant cells enter G1 of interphase following
cytokinesis, thus completing the cell cycle

Meiosis
Meiosis separates homologous chromosomes, producing haploid
daughter nuclei
Meiosis is a specialized cell division process that produces
haploid gametes
Each gamete receives one member of each pair of homologous
chromosomes
Meiosis consists of one round of DNA replication, followed by
two rounds of nuclear divisions

One round of DNA replication produces two chromatids in each
duplicated chromosome
Because diploid cells have pairs of homologous chromosomes,
with two chromatids per homologue, a single round of DNA
replication creates four chromatids for each type of chromosome
The first nuclear division, meiosis I, separates the pairs of
homologues, with each daughter nucleus receiving one. Each
daughter nucleus is haploid, even though each homologue it
receives had two chromatids
The second nuclear division, meiosis II, separates the
chromatids and parcels one chromatid into each of two more
daughter nuclei

At the end of meiosis, there are four haploid daughter nuclei,
each with one copy of each homologous chromosome
Meiotic cell division normally produces four haploid cells from
a single diploid parent cell
Meiosis Is a Reduction Division That Halves the Number of
Chromosomes
Importance of Meiosis
Fusion of gametes keeps the chromosome number constant
between generations

Meiosis reduces the chromosome number by half, producing
haploid (n) gametes (eggs and sperm)
Fusion of the gametes (fertilization) combines the two haploid
chromosome sets to produce a diploid (2n) zygote
If halving of the chromosome number did not occur in gametes,
sexual reproduction would double the chromosome number in
each new generation, leading to inviability
Meiotic Cell Division Is Essential for Sexual Reproduction

Meiotic Cell Division in an Animal Cell
Meiotic Cell Division in an Animal Cell
The life cycles of all eukaryotic organisms have a common
overall pattern
Two haploid cells from different parental organisms fuse during
the process of fertilization, creating a diploid cell with new
gene combinations
Meiotic cell division occurs, re-creating haploid cells
Mitotic cell division results in the growth of multicellular
bodies, or in asexual reproduction

The Human Life Cycle
Chapter-5
Cell membrane structure and function

Chapter at a glance
How Is the Structure of a Membrane Related to Its Function?
How Do Substances Move Across Membranes?
How Do Specialized Junctions Allow Cells to Connect and
Communicate?
Functions of the plasma membrane:
It isolates the cell’s contents from the external environment
It regulates the exchange of essential substances
It allows communication between cells
It creates attachments within and between cells
It regulates biochemical reactions

Phospholipids are responsible for the isolating function of
membranes
Proteins are responsible for selectively exchanging substances
and communicating with the environment, controlling
biochemical reactions, and forming attachments
Membrane structure
Membranes are “fluid mosaics” in which proteins move within
layers of lipids
The “fluid mosaic” model of a membrane was proposed in 1972
by S. J. Singer and G. L. Nicolson
This model indicates that each membrane consists of a mosaic,
or “patchwork,” of different proteins that constantly shift and
flow within a viscous fluid formed by a double layer of
phospholipids
The phospholipid bilayer is the fluid portion of the membrane
It consist of two very different parts:

A polar, hydrophilic head
Two nonpolar, hydrophobic tails
Plasma membranes face both exterior and interior watery
environments
Water-soluble substances such as salts, amino acids, and sugars
cannot easily cross phospholipid bilayers
However, very small molecules such as water, oxygen, and
carbon dioxide as well as larger, lipid-soluble molecules can

pass through this selective barrier
A variety of proteins form a mosaic within the membrane
Proteins are embedded within, or attached to, the phospholipid
bilayer
Many proteins have attached carbohydrates (glycoproteins) on
their outer membrane surface
Categories of membrane proteins

Receptor proteins
Recognition proteins
Enzymatic proteins
Attachment proteins
Transport proteins
Receptor and Recognition proteins

1. Receptor proteins trigger cellular responses upon binding of
specific molecules, such as hormones, sent by other cells
2. Recognition proteins are glycoproteins that serve as
identification tags on the surface of a cell
3. Enzymatic proteins are proteins that promote chemical
reactions that synthesize or break apart biological molecules
4. Attachment proteins
anchor the
- cell membrane to the inner cytoskeleton,
-to proteins outside the cell,
- to other cells
Transport proteins: Regulate the movement of hydrophilic

molecules through the membrane
There are two types of transport proteins
Channel proteins form channels whose central pores allow
specific ions or water molecules to pass through the membrane
Carrier proteins have binding sites that can temporarily attach
to specific molecules on one side of the membrane and then
move them through the membrane to the other side
Understanding molecular movement
A fluid is a substance whose molecules can flow past one
another and, therefore, have no defined shape
A solute is a substance that can be dissolved (dispersed as
atoms, ions, or molecules) in a solvent

A solvent is a fluid capable of dissolving a solute
Gradient
The concentration of a substance defines the amount of solute in
a given amount of solvent
A gradient is a physical difference in temperature, pressure,
charge, or concentration of a particular substance in a fluid
between two adjoining regions of space
Gradients cause molecules to move from one place to another
Gradients of concentration or pressure cause molecules or ions
to move from one region to another in a manner that tends to

equalize the difference
Cells use energy and cell membrane proteins to generate
concentration gradients of various molecules and ions dissolved
in their cytoplasm
Why gradients cause molecules to move from one place to
another:
Molecules and ions in solution are in constant random motion
An increase in temperature increases the rate of this random
motion
Random motion produces a net movement from regions of high
concentration to regions of low concentration by a process
called diffusion

Diffusion
Plasma membranes are selectively permeable because
they only allow only certain ions or molecules to permeate
There are two types of movement across the plasma membrane
Passive transport is the diffusion of substances across cell
membranes down concentration gradients
Energy-requiring transport is transport that requires the use of
cellular energy

Passive transport
Passive transport includes :
simple diffusion,
facilitated diffusion,
osmosis

Simple diffusion: Substances move down their concentration
gradients across a membrane.
Examples include water, oxygen, carbon dioxide, and lipid-
soluble molecules like alcohol and vitamins A, D, and E
Facilitated diffusion: Water soluble molecules like ions, amino
acids, and sugars diffuse down their concentration gradients
with the aid of channel and carrier transport proteins
Many cells have specialized water channel proteins called
aquaporins.Their small size and positive charges attract the
negative pole of water molecules making aquaporins selective
for water molecules

Types of Diffusion Through the Plasma Membrane
Osmosis
Osmosis is the diffusion of water across selectively permeable
membranes
Water diffuses from a region of high water concentration to one
of low water concentration across a membrane
Dissolved substances reduce the concentration of free water
molecules in a solution
Dissolved substances displace water molecules, lowering water
concentration
Dissolved substances form hydrogen bonds with water
molecules, reducing the number that are free to move across a
water-permeable membrane
Types of solution
Isotonic solutions have equal concentrations of water and equal
concentrations of dissolved substances
-No net water movement occurs across the membrane
A hypertonic solution is one with a greater solute concentration

Water moves across a membrane toward the hypertonic
solution
A hypotonic solution has a lower solute concentration
Water moves across a membrane away from the hypotonic
solution
The effects of osmosis are illustrated when red blood cells are
placed in various solutions
When cells are placed into a hypertonic solution, they shrivel,
owing to water loss
When cells are placed into a hypotonic solution, they swell,
owing to water entry
Cells in isotonic solutions remain unaffected

Active transport/energy requiring transport
During active transport, membrane proteins use cellular energy
to move molecules or ions across plasma membranes against
their concentration gradients
Active transport proteins span the entire membrane
They often have a molecule binding site and an ATP binding
site
When the high-energy third phosphate of bound ATP is
released, some of its stored energy is donated to the protein to
move molecules against gradients
Active transport proteins are often referred to as pumps

Active transport
recognition
site
Cells engulf particles or fluids by endocytosis. The engulfed
particles are transported within the cell inside vesicles
There are three types of endocytosis
Pinocytosis (“cell drinking”) moves liquids into the cell
Receptor-mediated endocytosis moves specific molecules into
the cell
Phagocytosis (“cell eating”) moves large particles into the cell

Receptor-Mediated Endocytosis
The plasma membrane extends pseudopods toward an
extracellular particle (for example, food). The ends of the
pseudopods fuse, encircling the particle. A vesicle called
a food vacuole is formed containing the engulfed particle.
Phagocytosis
Exocytosis
Exocytosis moves material out of the cell

--Cells use energy to dispose of undigested particles of waste or
to secrete substances into the extracellular fluid by exocytosis
--Vesicles containing the material to be expelled move to the
cell surface, where they fuse with the cell membrane, allowing
their contents to diffuse into the outside fluid
Attachment Proteins
Desmosomes attach cells together
Desmosomes are found where cells need to adhere tightly
together under the stresses of movement
Examples include the skin, intestine, and urinary bladder
Tight junctions make cell attachments leakproof
Tight junctions are found where tubes and sacs must hold
contents without leaking
Examples include the skin and the urinary bladder

Gap junctions and plasmodesmata allow direct communication
between cells
Cell-to-cell protein channels allowing for passage of hormones,
nutrients, and ions in animal cells are gap junctions
Plant cells have holes in the walls of adjacent cells forming
cytoplasmic connections called plasmodesmata
INTRODUCTORY BIOLOGY (BIOL-1411)
FALL SEMESTER-2014
Worksheet chapter-5 Cellmembrane and function
I. Choose the correct answer: (0.25 points each)
1. Channel proteins that allow water to pass through them are
called _________
a. Glycoprotein’s

c. Aqua proteins
b. Gap junctions
d. Desmosomes
2. Osmosis means ___________________________.
a. Movement of water
c. movement of solute
b. Movement of solution
d. neither of them
3. If a cell is placed in a Isotonic solution, the cell will
_________
a. swell
c. shrink
b. remain the same
d. none of the above
4. If a cell is placed in a hypotonic solution, the cell will ___
_____
a. swell
c. shrink
b. remain the same
d. none of the above

5. The fluid mosaic membrane describes the membrane as
a. containing a huge quantity of water in the interior
b. composed of fluid phospholipids on outside and proteins on
inside
c. composed on protein outside and fluid phospholipid inside
d. made of proteins and lipids that can freely move
6. Which of the following is not a mechanism for bringing
material into the cell?
a. Exocytosis
c. Pinocytosis
b. Endocytosis
d. Phagocytosis
7. Which of these types of cellular transport requires energy
a. facilitated diffusion
c. osmosis
b. Active transport

d. a and b
8. What chemical property characterizes the interior of the
phospholipid bilayer
a. It is hydrophobic
c. IT is polar
b.it is hydrophilic
d.it is saturated
9. If someone at the other end of a restaurant smokes a
cigarette, you may breathe in some smoke. The movement of
smoke is similar to what type of transport.
a. osmosis
c. diffusion
b. facilitated diffusion
d. active transport
10. plasma membrane is made up of a ________
a. lipid layer

c. lipid bilayer
b. phospholipid layer
d. phospholipid bilayer
II. Answer whether true or false: (0.25 points each)
1. Diffusion is movement of water from a region of low
concentration to a region of high concentration. ( )
2. If phagocytosis means eating solid particles, pinocytosis
means drinking solid particles. ( )
3. In plant, cell to cell connection is due to the presence of
plamodesmata. ( )
4. A membrane that allows certain things to pass through it and
prevents certain things to pass is called permeable membrane. (
)
5. Gradient means a physical difference such as temperature,
pressure, concentration etc between two regions. ( )
III. Choose any three questions and Write any four differences
between them (each question 1 point).
1. Identify the picture and explain the process in few points
2. The picture shows human red blood cell in different
solutions. Explain what happens to the cell in each solution
3. Active transport and passive transport
4.Simple diffusion and facilitated diffusion
5.Define hypotonic, hypertonic, and isotonic. What would be
the fate of an animal cell immersed in each of these three types
of solution?
6. Briefly write about the structure and function of plasma
membrane.
INTRODUCTORY BIOLOGY (BIOL-1411)

FLL SEMESTER-2014
I. Choose the right answer:
1. Bacteria divides to produce daughter cells by the process of
_________
a. Mitosis
c. Binary fission
b. Meiosis
d. None of them
2. During meiosis gametes produced have _________number of
chromosome.
a. Diploid
c. both of them
b. Haploid
d. None of them
3. Sister chromatids are aligned in the centre of the cell during
_________stage
a. Prophase
c. Telophase
b. Metaphase

d. Anaphase
4. Chromosomes attach to fibers at structures called
__________________.
a. Telomeres
c. Centromeres
b. Genes
d. neither of them
5. Which of the following is not a function of mitosis in
humans?
a. Repair of wounds
c. Production of gametes
b. growth
d. Replacement of lost cells
6. A biochemist measures the amount of DNA in cells growing
in the lab. The quantity of DNA in a cell would be found double
a. Between prophase and anaphase
c. Between metaphase and telophase
b. between G1 and G2 of cell cycle d. during M phase of
cell cycle

7. In comparing somatic cells and gametes, somatic cells are
a. diploid with half the number of chromosomes
b. haploid with half the number of chromosomes
c. diploid with twice the number of chromosomes
d. haploid with twice the number of chromosomes
8. What are homologous chromosomes?
a. two halves of a replicated chromosomes
b, two identical chromosomes from one parent
c. two identical chromosomes, one from each parent
d. Two similar chromosomes, one from each parent.
9. Duplicated chromosomes consist of two identical DNA
double helices, called __________.
a. Homologous
c. Sister Chromatids
b. Chromatin strands
d. neither of them
II. Answer whether true or false: (0.25 points each)
1. Diploid means n chromosomes and haploid means 2n
chromosomes.
2. If an intestinal cell in a dog contains 78 chromosomes, a dog

sperm cell would contain ______chromosomes
3. A micrograph of a dividing mouse cell shows 19
chromosomes each consisting of two sister chromatids. During
which stage of meiosis could this picture be taken,
4. Meiosis is a cell division that occurs only in sex cells
5. Prophase is the last stage in mitosis where the two daughter
cells separate
6. Cell cycle involves the G1, S and G2 phase only.
7. Cytokinesis in plant cells takes place by the formation of cell
plate
8. Movement of sister chromatids to the same pole occurs in
meiosis.
9. During meiosis there is only one round of replication for two
divisions
10. Gametes are diploid with double the number of
chromosomes
III. Answer any four of the following ( each carries 1.5 mark)
1. Diagram and describe the eukaryotic cell cycle. Name the
various phases, and briefly describe the events that occur during
each.
LABEL THE PARTS FROM PRESENTATION OR TEXT
1. Eukaryotic cell cycle is divided into two major phases:
interphase and cell division
2. Interphase is the stage where the cell acquires nutrients from
its environment, grows and duplicates its chromosomes it
contains three sub phases
G1_ a newly formed daughter cell enters this stage, and carries
out activities like: it grows in size, specializes to perform
specific function and it decides whether to divide or not, and
enters the next phase

S-phase: DNA synthesis takes place via semiconservative
replication
G2: cell grows some more and then synthesize the proteins
needed for cell division.
Cell division: cell carries out either mitosis or meiosis’ in order
to form new daughter cells
2. Explain the process of Mitosis.
Mitosis consists of nuclear division followed by cytoplasmic
division.
Mitosis occurs in the following phases
1: Prophase is the first phase, duplicated chromosome condense,
spindle microtubules form , chromosomes are captured by
microtubules
2 : Metaphase – duplicated chromosome are connected to
spindle fibers leading to opposite poles of the cell.
Microtubules shorted and lengthen until each chromosome lines
up along the equator of the cell
3: Anaphase- sister chromatids formed during S-phase separates
becoming independent daughter chromosomes, one of the 2
daughter chromosomes from each original parental
chromosomes move to each pole of the cell
4: telophase- spindle fibers disintegrate nuclear envelope forms
around each group of chromosome. The DNA revert to its
original extended state, nucleoli begin to form
5: cytokinesis- microfilaments attached to membrane form a
ring around the equator of the cell, constricts dividing the cell,
in plants cell plate is formed forming 2 daughter cells
3. Compare the process of cytokinesis in plant cell and animal
cell.

Cytokinesis in animal cells
a. Microfilaments attached to the plasma membrane form a ring
around the equator of a cell . The ring contracts and constricts
the cell’s equator
b. Eventually, contraction of the ring pinches off the membrane,
forming two daughter cells, each with a nucleus identical with
the other
c. Following cytokinesis, animal cells enter G1 of interphase,
thus completing the cell cycle
a. Stiff plant cell walls prevent the “pinching off” of
cytokinesis seen in animal cells, which only have a plasma
membrane
b. Instead, carbohydrate-filled vesicles assemble along the
cell’s equator, between the daughter nuclei
c.The vesicles fuse into a continuous flattened sac, surrounded
by plasma membrane and filled with sticky carbohydrates .This
is called a cell plate
d. The plasma membranes of the plate fuse with the plasma
membrane of the cell, forming two cells, with the carbohydrate
in between becoming part of the cell wall
e. As in animals, plant cells enter G1 of interphase following
cytokinesis, thus completing the cell cycle
4. Describe in humans the three categories of cells, based on
their ability to divide and differentiate

1.Stem cells :
- have two important characteristics: self-renewal, and the
ability to differentiate into a variety of cell types
-Stem cells self-renew because they retain the ability to divide,
perhaps for the entire life of the organism
-Some stem cells in early embryos can produce any of the
specialized cell types of the entire body
2.Other cells capable of dividing
-Some cells other than stem cells are capable of continuing to
divide, but typically differentiate into only one or two different
cell types
· Dividing liver cells, for example, can only become more liver
cells
· Permanently differentiated cells differentiate and never
divide again
· For example, most heart and brain cells cannot divide
5. Complete the following table to compare mitosis and meiosis
mitosis
Meiosis
a. Number of chromosomal duplications
b. Number of cell divisions

c. Number of daughter cells produced
d. Number of chromosomes in daughter cells
e. How chromosomes line up during metaphase
f. Genetic relationship of daughter cells to parent cells
g. functions performed in the human body

Chapter-6Cell Cycle and DivisionCell Divisio.docx

Recommended

Recommended

More Related Content

Similar to Chapter-6Cell Cycle and DivisionCell Divisio.docx

Similar to Chapter-6Cell Cycle and DivisionCell Divisio.docx (20)

More from christinemaritza

More from christinemaritza (20)

Recently uploaded

Recently uploaded (20)

Chapter-6Cell Cycle and DivisionCell Divisio.docx