Download Control of Cell Division

Cells
Dr. Gary Mumaugh
Introduction
• The cell is the basic unit of biological organization
• Basic composition
– protoplasm
– cell membrane
– Organelles
• Human cells vary in size, shape and function
– From microscopic to up to two feet long
• There are 50-100 trillion cells in the human body.
• Differentiation is when cells specialize.
• There are over 260 different kinds of human cells.
• As a result of differentiation, cells vary in size and
shape due to their unique function
Anatomy of a Typical Cell
The Cell Membrane
• Double phospholipid layer with embedded
proteins – also called Plasma Membrane
– Protein functions of include forming channels
or pores, transporters, receptor sites for
hormones
• Cell membranes are selectively permeable
membranes
– Only certain substances can get through
• Not everything is on the “A” list !
Cytoplasm of the Cell
• Mostly water with chemical compounds
in solution or colloid
– Solution: atoms or ions distributed in
medium
• Polar compounds go into solution
• Nonpolar compounds go into colloidal
suspension
The Nucleus
• All human cells have a nucleus
– Except the RBC
• Control center of the cell
• Nuclear membrane has pores to allow substances
passage
• Chromatin genetic material (long threads of
chromosomes) are inside nucleoplasm
• Nucleolus - site of ribosome formation
Cytoplasm
• Is the watery solution of minerals, gases, organic
molecules and cell organelles that is found between
the cell membrane and the nucleus
• Cytosol is the water portion of the cytoplasm
• Many of the chemical reaction that occur in the cell
happen in the cytoplasm
Endoplasmic Reticulum (ER)
• System of membranes that makes up channels
• Connects with outer nuclear and cell membranes
• Types of ER
– Rough: for protein synthesis attached ribosomes
– Smooth: fat transport and sex hormone synthesis
Ribosomes
• Very small structures made up of protein and
ribosomal RNA
• Distributed throughout cytoplasm
• Attached to rough Endoplasmic Reticulum
• Site of protein synthesis
The Golgi Apparatus
• Secretion is the task of the Golgi apparatus
– They produce specific proteins to be used elsewhere
in tissues
– To secrete a substance, small sacs of the membrane
break off and fuse with the cell membrane, releasing
the substance to the outside of the cell
– This is called exocytosis
•
•
•
•
Collection of flat saclike cisternae
Concentration and collection of cellular compounds
Storage warehouses of the cell
Carbohydrate synthesis site
The Mitochondria
• Powerhouses of the cell
• The aerobic (oxygen requiring) reactions of cell
respiration take place here
• The site of ATP and energy production
• Cristae - inner folds where cellular respiration occurs
• Energy requirements of cell determine cristae
number
Lysosomes
• Digestive enzyme packages
• When WBC engulf bacteria, the bacteria are
digested and destroyed by lysosomal enzymes
• Worn out cell parts and dead cells are digested by
the lysosomes
• Function
– digest stored food
– maintenance and repair of organelles
– suicide agents for old or weak cells
Centrioles
•
•
•
•
Involved in cellular division and reproduction
Form spindle fibers during cell division
Guide duplicated chromosomes to daughter cells
Centrosome - two centrioles at right angles to each
other
Cilia and Flagella
•
•
•
•
Hairlike protrusions from cell membrane
Nine double fibrils around two single central fibrils
Cilia move materials across cell surface
Flagellum propels cell through a medium
Functions of Cell Organelles
• ER - Transport of materials in the cell
•
•
•
•
•
•
•
Ribosomes – Site of protein synthesis
Golgi apparatus – Cell secretion
Mitochondria – ATP production, cell powerhouse
Lysosomes – Digestive enzymes
Centrioles – Cell division
Cilia – Sweeps material across the cell surface
Flagellum – Enables a cell to move
Think of the “Cell Factory”
Boss give orders to the rest of the factory (DNA in the
nucleus surrounded by the nuclear membrane). The
workers (ribosomes) on the assembly line are in the factory
(cytosol) who receive orders for production from the boss’s
messanger (mRNA). The raw materials are the amino
acids. When things are sent to the mailroom for outside
delivery (golgi apparatus), they are eventually shuttled to
the gates of the factory (secretory vessels).The gate of the
factory controls shipment in and out (cell membrane). The
turbines provide power for the factory (mitochondria).
Movement of Materials Into and
Out of Cells
Passive (Physical)
Processes
Active (Physiological)
Processes
• Require no cellular
energy and include:
• Simple diffusion
• Facilitated diffusion
• Osmosis
• Filtration
• Require cellular energy
and include:
• Active transport
• Endocytosis
• Exocytosis
• Transcytosis
Diffusion
• Movement of molecules from area of high
concentration to low concentration
• Brownian movement - random collision of diffusing
molecules
• Accelerated by increased temperature
• Gas exchange in the lungs of body tissue is an
example
– O2 - CO2 exchange
.
Animation: How Diffusion Works
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Facilitated Diffusion
• Facilitate means to help or assist
• Molecules move from an area of greater
concentration to an area of lesser concentration, but
they need help
– An example is glucose, which is need for ATP
production. Glucose can’t get through membranes by
themselves, so they have a carrier enzyme or
transporter to help facilitate diffusion
Animation: How Facilitated Diffusion Works
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Animation: Diffusion Through Cell
Membranes
Please note that due to differing
operating systems, some animations
will not appear until the presentation is
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Osmosis
• Movement of water through semipermeable
membrane from high water concentration to low water
concentration
• Absorption of water by the small intestines and kidney
is an example
– Isotonic solution - salt concentration is the same outside
the cell as inside
– Hypotonic solution - salt concentration inside cell is
higher than outside cell
– Hypertonic solution -salt concentration higher outside
the cell than inside
Animation: How Osmosis
Works
Please note that due to differing
operating systems, some animations
will not appear until the presentation is
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27
.
• Osmotic Pressure – ability of osmosis to generate
enough pressure to move a volume of water
• Osmotic pressure increases as the concentration
of nonpermeable solutes increases
(a)
• Isotonic – same osmotic
pressure
• Hypertonic – higher osmotic
pressure (water loss)
• Hypotonic – lower osmotic
pressure (water gain)
(b)
(c)
Active Transport
• The movement of molecules from and area of lesser
concentration to an area of greater concentration
• Opposite of diffusion
• Requires the energy of ATP to do this
• An example in the body is sodium and potassium
pumps in muscle and nerve cells
Filtration
• Water and dissolved materials are forced through a
membrane from an area of higher pressure to an
area of lower pressure
• In the body, blood pressure is an example of this,
with filtration occurring through the capillaries
Phagocytosis and Pinocytosis
• Phagocytosis
– A moving cell engulfs something
– WBC engulfing bateria
– Think of “pacman”
• Pinocytosis
– A stationary cell engulfs something
– Kidney cells absorbing lost protein
.
Endocytosis
• Cell engulfs a substance by forming a vesicle around
the substance
• Three types:
• Pinocytosis – substance is mostly water
• Phagocytosis – substance is a solid
• Receptor-mediated endocytosis – requires the
substance to bind to a membrane-bound receptor
Cell
membrane
Nucleus Nucleolus
Vesicle
Endocytosis
Cell
Particle
membrane
Phagocytized
particle
Vesicle
Nucleus Nucleolus
Receptor-ligand
combination
Molecules
outside cell
Vesicle
Receptor
protein
Cell
membrane
Cell
membrane
indenting
Cytoplasm
(a)
(b)
(c)
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(d)
Exocytosis
• Reverse of endocytosis
• Substances in a vesicle fuse with cell membrane
• Contents released outside the cell
• Release of neurotransmitters from nerve cells
Endoplasmic
reticulum
Golgi
apparatus
Nucleus
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DNA and the Genetic Code
• DNA is a double helix strand of nucleotides, looking
like a spiral ladder
– The rungs of the ladder are made up of four different
bases, arranged in different orders and sequences
– These sequences are the genetic code
– The DNA of our 46 chromosomes is the genome
which contains 20,000 to 30,000 genes
• If there is a mistake in the DNA, the result is genetic
or hereditary disease
RNA and Protein Synthesis
• Protein Functions
– structure, enzymes or catalysts, immune response
• Transcription Messenger RNA copies DNA code,
leaves nucleus
• Translation (tRNA) picks up amino acids
Cell Division
• Cell division is the process by which a cell
reproduces itself
• Two types of cell division
– Mitosis
– Meiosis
Mitosis
• One cell with the diploid number of chromosomes
divides once to form two cells, each with the diploid
number of chromosomes (46)
• Stages of mitosis
– Prophase, metaphase, anaphase, telophase
• Mitosis is essential for growth and for repair and
replacement of damaged cells
• Most nerve and muscle cells seem unable to divide and
their loss may involve permanent loss of function
Meiosis: A Reduction Division
• Reduces genetic material from diploid to haploid
• Two divisions resulting in four cells
• Occurs only in the gonads
– In women, meiosis takes place in the ovaries and is
called oogenesis
– In men, meiosis takes place in the testes and is called
spermatogenesis
• Fertilization is the egg uniting with the sperm
Comparison of Mitosis and Meiosis
Mitosis
Two daughter cells with
exact same genetic
material
Cellular division for
growth, maintenance
and repair
Meiosis
Four daughter cells with
half the genetic material
Cellular division for
reproduction
3.5: Control of Cell Division
• Cell division capacities vary greatly among cell types
• Skin and blood cells divide often and continually
• Neuron cells divide a specific number of times then cease
• Chromosome tips (telomeres) that shorten with each mitosis
provide a mitotic clock
• Cells divide to provide a more favorable surface area to
volume relationship
• Growth factors and hormones stimulate cell division
• Hormones stimulate mitosis of smooth muscle cells in uterus
• Epidermal growth factor stimulates growth of new skin
• Contact (density dependent) inhibition
• Tumors are the consequence of a loss of cell cycle control
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Tumors
• Two types of tumors:
• Benign – usually remains
localized
• Malignant – invasive and can
Normal cells
(with hairlike cilia)
metastasize; cancerous
• Two major types of genes
cause cancer:
• Oncogenes – activate other
genes that increase cell division
• Tumor suppressor genes
– normally regulate mitosis; if
inactivated they are unable to
regulate mitosis
• Cells are now known as
“immortal”
Cancer cells
Cellular Metabolism
• Metabolic processes – all chemical reactions that
occur in the body
There are two (2) types of metabolic reactions:
• Anabolism
• Larger
molecules are
made from
smaller ones
• Requires energy
• Catabolism
• Larger molecules
are broken down
into smaller ones
• Releases energy
Anabolism
• Anabolism provides the materials needed for
cellular growth and repair
• Dehydration synthesis
• Type of anabolic process
• Used to make polysaccharides, triglycerides, and
proteins
• Produces water
.
CH2OH
CH2OH
O
H
O
H
H
CH2OH
H
O
H
H
CH2OH
H
O
H
H
H
H
H
H2O
HO
OH
H
H
OH
HO
OH
Monosaccharide
+
OH
H
H
OH
Monosaccharide
OH
HO
OH
H
H
OH
O
Disaccharide
OH
H
H
OH
+
OH
Water
Catabolism
• Catabolism breaks down larger molecules into smaller on
• Hydrolysis
• A catabolic process
• Used to decompose carbohydrates, lipids, and protei
• Water is used to split the substances
• Reverse of dehydration synthesis
CH2OH
CH2OH
O
H
O
H
H
CH2OH
H
O
H
H
CH2OH
H
O
H
H
H
H
H
H2O
HO
OH
H
H
OH
HO
OH
Monosaccharide
+
OH
H
H
OH
Monosaccharide
OH
HO
OH
H
H
OH
O
Disaccharide
OH
H
H
OH
+
OH
Water
Control of Metabolic Reactions
• Enzymes
• Control rates of metabolic reactions
• Lower activation energy needed to start reactions
• Not consumed in chemical reactions
.
Substrate molecules
Product molecule
Active site
Enzyme
molecule
(a)
Enzyme-substrate
complex
(b)
(c)
Unaltered
enzyme
molecule
46
Animation: How Enzymes Work
Please note that due to differing
operating systems, some animations
will not appear until the presentation is
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47
Factors That Alter Enzymes
• Factors that alter enzymes:
• Heat
• Radiation
• Electricity
• Chemicals
• Changes in pH
Energy for Metabolic Reactions
• Energy is the capacity to change something; it
is the ability to do work
• Common forms of energy:
• Heat
• Light
• Sound
• Electrical energy
• Mechanical energy
• Chemical energy
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