Download Cell Structure and Function

Cell Structure and Function
Cell theory:
Cells are basic structural units of all plants and
animals.
Cells are the smallest functioning units of life.
Cells are produced only by the division of
prexisting cells.
Each cell maintains homeostasis.
Our bodies maintain homeostasis through combined
action of trillions of cells.
Anatomy and Physiology for Engineers
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Types of Cells (X 500 mag.)
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Cellular Anatomy
Anatomy and Physiology for Engineers
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Cellular Anatomy: Membrane
Lipid bilayer that separates cyotplasm from extracellular fluid.
Functions of cellular membrane:
Physical isolation; Regulation of exchange with environment;
Sensitivity; Structural support.
Composed of:
lipids
proteins
carbohydrates.
Anatomy and Physiology for Engineers
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Cell Membrane
Major components: lipids, proteins, carbohydrates.
Lipids:
Phospholipids
Phosphate group (PO43-) linked to diglyceride (glycerol +
2 fatty acid tails) and to a non-lipid head.
2 layers: heads on outside, tails on inside.
Often called the phospholipid bilayer.
Allows lipid-soluble substances (alcohol, fatty
acids,steroids) to diffuse through.
Water soluble compounds must find other ways to move
through the membrane (i.e., through selective channels).
Anatomy and Physiology for Engineers
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Cell Membrane
Major components: lipids, proteins, carbohydrates.
Proteins:
Several types of proteins, found either embedded
within the layer or bound to inner or outer
surfaces.
Various functions:
Receptors,
Anatomy and Physiology for Engineers
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Protein Receptors: Insulin
Anatomy and Physiology for Engineers
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Cell Membrane
Major components: lipids, proteins, carbohydrates.
Proteins:
Several types of proteins, found either embedded
within the layer or bound to inner or outer
surfaces.
Various functions:
Receptors, channels,
Anatomy and Physiology for Engineers
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Protein channels: Ion Channels
Anatomy and Physiology for Engineers
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Cell Membrane
Major components: lipids, proteins, carbohydrates.
Proteins:
Several types of proteins, found either embedded
within the layer or bound to inner or outer
surfaces.
Various functions:
Receptors, channels, carriers,
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Protein carriers: Glucose Carrier
Anatomy and Physiology for Engineers
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Cell Membrane
Major components: lipids, proteins, carbohydrates.
Proteins:
Several types of proteins, found either embedded
within the layer or bound to inner or outer
surfaces.
Various functions:
Receptors, channels, carriers, enzymes,
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Protein Enzymes: Digestive Enzymes
lining GI Tract,
Anatomy and Physiology for Engineers
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Cell Membrane
Major components: lipids, proteins, carbohydrates.
Proteins:
Several types of proteins, found either embedded
within the layer or bound to inner or outer
surfaces.
Various functions:
Receptors, channels, carriers, enzymes, anchors,
Anatomy and Physiology for Engineers
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Protein Anchors: Epithelial cells anchored
to basement membrane
Anatomy and Physiology for Engineers
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Cell Membrane
Major components: lipids, proteins, carbohydrates.
Proteins:
Several types of proteins, found either embedded
within the layer or bound to inner or outer
surfaces.
Various functions:
Receptors, channels, carriers, enzymes, anchors,
identifiers.
Anatomy and Physiology for Engineers
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Protein Identifiers:
Recognition of Antigen
Bound to the
Major
Histocompatibility
Complex (MHC)
Protein by
Cytotoxic T cells
Anatomy and Physiology for Engineers
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Cell Membrane
Major components: lipids, proteins, carbohydrates.
Proteins:
Several types of proteins, found either embedded within
the layer or bound to inner or outer surfaces.
Various functions:
Receptors, channels, carriers, enzymes, anchors, identifiers.
Proteins “float” from location to location on the cell
membrane.
Protein composition of membrane can change from time
to time as proteins are added or removed.
Anatomy and Physiology for Engineers
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Cell Membrane
Major components: lipids, proteins, carbohydrates.
Carbohydrates:
Act as lubricants on outer surface of cell
membrane.
Act as receptors for extracellular components.
Prevent immune system from attacking cell.
Provides recognition signals to immune-system
proteins.
Anatomy and Physiology for Engineers
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Membrane Transport
Permeability of cell membrane determines which
substances enter/leave cell.
Selectively permeable.
Passage based on size, electron charge, shape, and lipid
solubility.
Passive –vs- active transport.
Passive: no energy expenditure.
Active: requires energy (usually in the form of ATP ‡
ADP + Energy).
Diffusion
Net passive movement of molecules along a concentration
gradient.
Examples: CO2 diffusion out of a cell; O2 diffusion into a
cell.
Anatomy and Physiology for Engineers
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Diffusion across cell membranes
Although water and dissolved solutes diffuse freely
through extracellular fluid, cell membrane permits
only selective diffusion.
Primary factors that
determine diffusion
across cell membrane:
Size & lipid solubility.
Size‡ pass through
various membrane
channels (< 0.8 nm).
Solubility ‡ pass
through lipid bilayer.
Water soluble
molecules must go
through channels. Anatomy and Physiology for Engineers
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Osmosis
Special type of diffusion involving only water molecules.
Depends of the total concentration of solutes in water
solution.
Total concentration of solutes on both sides of cellular
membrane always remains the same ‡ Why ?
Cell membrane is freely permeable to water but not to other larger
molecules.
Water molecules will diffuse in or out based on the trans-membrane
H2O concentration gradient.
Osmotic pressure: Amount of hydrostatic pressure required to
prevent osmosis across a membrane.
Greater the solute concentration ‡ greater the osmotic pressure.
Anatomy and Physiology for Engineers
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Osmosis
Osmotic pressure
Effect of extracellular
concentration on RBC
Extracellular solution can be:
Hypertonic: Solution with larger
number of solutes.
Isotonic:
Solution with equal
concentration of
solutes.
Hypotonic: Solution with smaller
solute concentration.
Normal saline: 0.9% NaCl in solution
‡mimics normal osmotic
concentration of extracellular fluid.
Anatomy and Physiology for Engineers
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Filtration
Passage of H2O and other small molecules
through a membrane as a result of a
hydrostatic pressure gradient.
Larger solutes may not pass through due to
size of membrane pores.
Occurs across capillary membrane; kidneys;
etc.
Filtration of H2O, dissolved nutrients from capillaries into tissue
Parterial=100 mm Hg
Pvenous=30 mm Hg
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Carrier-Mediated Transport
Proteins on cell membranes that transport carriers of specific
ions and/or organic substances across cellular membrane.
Substances move by “piggy-backing” on protein.
Transport process can be passive or active (ATP required).
Passive: Facilitated diffusion.
Active: Active transport.
Facilitated Diffusion
Anatomy and Physiology for Engineers
Active Transport
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Vesicular Transport
Movement of material into or out of
cell through the formation of vesicles.
Vesicles: small membranous sacs that
enclose the compound to be moved.
Endocytosis: Transport into the cell.
Pinocytosis (cell drinking):
Vesicle forms around extracellular fluid
at cell membrane which then pinches
off inside the cell.
Phagocytosis (cell eating)
Vesicle forms around solid objects
Usually part of the immune response.
WBC ‘eating’
old RBC
Exocytosis: Transport out of cell.
Vesicular transport requires energy.
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Back to Cell Structure
The Cytoplasm
Between membrane and nucleus, divided into cytosol and organelles.
Cytosol:
Intracellular fluid (55% of total cell volume).
Contains dissolved nutrients, ions, soluble and insoluble proteins.
Very different in composition from extracellular fluid.
High concentration of K+; low concentration of Na+.
High concentration of dissolved proteins.
Large reserves of amino acids and lipids.
Enzymatic regulation of intermediary metabolism.
Enzymes for degradation, synthesis and transformation of simple sugars, amino
acids, fatty acids are all found in cytosol.
Ribosome protein synthesis.
Free ribosomes found in cytoplasm synthesize proteins for use in cytosol.
Storage of fat and glycogen.
Excess nutrients not used for ATP production are stored in cytosol.
Ex: Adipose tissue ‡ specialized cells for storage of fat.
Anatomy and Physiology for Engineers
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Adipocyte
Cytosol is composed mainly of a large lipid droplet.
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Organelles
Structures that form specific functions necessary for
normal cell activity.
Like intra-cellular “specialty shops.”
Multiple activities can take place simultaneously without
chemicals from one activity (ex: enzymatic destruction of
proteins in lysosomes) harming other parts of the cell.
Two types:
Membranous (containing an outer membrane).
Nucleus, Mitochondria, Endoplasmic Reticulum, Golgi apparatus,
Lysosomes.
Non-membranous (no covering membrane).
Cytoskeleton, Micovilli, Centrioles, Cilia, Flagella, Ribosomes.
Anatomy and Physiology for Engineers
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Organelles – Cytoskeleton (Non-membranous)
Complex protein network that acts as cellular “bone and muscle.”
Composed of microfilaments and microtubules.
Microfilaments:
Thinnest strands (6 nm diam.)
Made from the protein actin.
Actin ‘pearls’ wound as a double strand.
Act as mechanical stiffeners for various
cellular projections.
Also important in cellular contraction.
Attach cell membrane to cytoplasm.
Microtubules:
Hollow tubes (22 nm diam) made from the
small globular protein tubulin.
Main function is to provide mechanical
rigidity, especially for asymmetrically shaped
cells (ex: nerve cell).
Form the spindle apparatus that distributes
duplicated chromosomes to opposite sides of
the dividing cell.
Anatomy and Physiology for Engineers
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Actin Molecules in Muscle Cell
Anatomy and Physiology for Engineers
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Organelles – Microvilli (non-membranous)
Small micro-filament supported finger-like
projections of the cellular membrane.
Presence of microvilli increases the area of
contact between cell membrane and extracellular fluid.
Found in cells lining the digestive tract and
the kidneys (facilitates absorption of
materials).
Anatomy and Physiology for Engineers
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Organelles – Centrioles, Cilia, Flagella
Centrioles
(non-membranous)
Short cylindrical structures important in cell division.
Composed of microtubules.
Cilia
Longer finger-like extensions of cell membrane.
Internal structure of microtubules provides mechanical support.
Coordinated movements of cilia produce movement of fluids, etc., across
cell membrane.
Ex: movement of mucus and trapped particles away from respiratory
tract and toward the throat.
Damage to cilia (excessive smoking /other metabolic problem) will
reduce “cleansing,” leading to chronic respiratory infections.
Flagella
Resemble cilia but much longer.
Responsible for moving the cell (ex: sperm cell).
Anatomy and Physiology for Engineers
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Organelles – Ribosomes (non-membranous)
Small particles that synthesize proteins under
direction from DNA.
Consists of ribosomal RNA and proteins.
Number of ribosomes in each cell varies depending
on cell function.
Liver cells contain many more ribosomes to synthesize
liver proteins than fat cells that synthesize triglycerides.
Ribosomes act as the “workbenches” for protein
assembly.
Two types:
Free ribosomes: scattered throughout the cytoplasm
Fixed ribosomes: part of the endoplasmic reticulum.
Anatomy and Physiology for Engineers
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Organelles – Endplasmic Reticulum
(membranous)
Elaborate fluid-filled membranous system distributed
throughout the cytosol.
ER has 3 major functions:
Synthesis of proteins, carbohydrates
and lipids.
Storage of synthesized substances.
Transport of material within cell.
Two types of ER:
Smooth ER (SER)
Lacks ribosomes.
Site of lipid and carbohydrate
synthesis.
Rough ER (RER)
Protein synthesis (lots of fixed
ribosomes).
Anatomy and Physiology for Engineers
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Steps in the muscular Contraction Process
Importance of the Sarcoplasmic (Endoplasmic) Reticulum
in Storing Ca2+ Ions
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Organelles – Golgi Apparatus (membranous)
Sets of flattened, slightly curved membranous sacs stacked in layers.
Number varies from 1 to 100’s depending on cell type.
Most newly synthesized molecules arrive at Golgi apparatus through
transport vesicles.
Finished products released via 3 different types of vesicles: secretory
vesicles (exocytosis); membrane protein transport vesicles; and lysosomes.
Functions:
Processing and direction of molecules into finished products.
Packaging of special enzymes for use in the cytosol.
Renewal or modification of cell membrane.
Anatomy and Physiology for Engineers
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Organelles – Lysosomes (membranous)
Small vesicles (0.2 – 0.5 mm) filled with powerful digestive
(hydrolytic) enzymes.
Membrane and enzymes are derived from Golgi apparatus.
Functions include:
Cleanup and recycling.
Fuse with membranes of damaged organelles.
Enzymes break down contents; nutrients enter cytoplasm; waste is ejected
via exocytosis.
Defense
Cells engulf bacteria and other debris (phagocytocis).
Lysosome fuses with membrane of the internalized vesicle.
Enzymes released into vesicle to destroy bacteria.
Apoptosis (programmed cell death)
Deliberate destruction of certain cells (ex: normal part of embryonic
development).
Anatomy and Physiology for Engineers
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Organelles – Mitochondria (membranous)
Energy organelles of the cells.
Produce energy for various cellular activities.
Contains various enzymes that regulate intra-organelle
chemical activity.
Double membrane structure:
Outer membrane covering entire organelle.
Inner membrane (cristae) containing numerous folds.
Matrix: fluid enclosed within cristae.
Enzymes are located on surface of cristae.
Folds provide large surface area.
Number of mitochondria within cell depends on energy
requirements of cell.
RBC‡ no mitochondria; Heart muscle cell:‡ several thousand.
Anatomy and Physiology for Engineers
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Organelles – Mitochondria (membranous)
Source of energy for the body is the chemical energy stored in the carbonhydrogen bonds in ingested food.
Body cells are not equipped to use this energy directly.
Need to extract this energy and convert it into ATP, the cellular energy
“currency.”
Mitochondria play the key role in producing ATP.
Organic molecules + O2 in ‡ CO2 + ATP out
Anatomy and Physiology for Engineers
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Organelles – Nucleus (membranous)
Control center of cellular operation.
Most cells contain a single nucleus.
Exceptions (mature RBC – no nucleus, skeletal muscle cells – many nuclei).
Structure: Nuclear envelope surrounding the nucleoplasm.
Nucleoplasm contains ions, enzymes, RNA & DNA nucleotides, proteins, small
amounts of RNA and DNA.
Chemical communication to cytoplasm takes place via nuclear pores: small
holes for passage of H2O, ions, small molecules (No proteins or DNA).
Nucleoli: Organelles that synthesize components of ribosomes.
Anatomy and Physiology for Engineers
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Organelles – Nucleus (membranous)
Chromosomes (within nucleus)
DNA + histones (proteins) ‡
chromosomes.
Each nucleus contains 23 pairs
chromosomes.
One member of each pair from
father; other from mother.
Level of coiling depends on
whether cell is dividing or not.
Extremely tight coiling within
dividing cells.
Loosely coiled structures
(chromatin) in non-dividing
cells.
DNA contains information to
code > 100,000 different
proteins.
Anatomy and Physiology for Engineers
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Genes and the Genetic Code
Basic structure of nucleic acids was discussed earlier.
Single DNA molecule consists of a pair of strands held together by
hydrogen bonding between complimentary nitrogenous bases (AAdenosine; T-Thymine; C-Cytosine; G-Guanine).
Information is stored in the sequence of the nitrogenous bases – this is
the genetic code.
Basic code segment is a triplet.
Sequence of 3 bases can specify identity of a single amino acid.
Each gene consists of all triplets needed to produce a specific
protein.
Since proteins consist of varying number of amino acids,
number of triplets within a gene can vary, i.e., size of gene
can vary.
Triplets also have ‘file start’ and ‘file end’ information.
Anatomy and Physiology for Engineers
Slide 3-43
Protein Synthesis
Each molecule of DNA consists of 1000’s of genes
‡ can code many 1000 proteins.
Genes are normally tightly coiled and bound to
histones: cannot be activated.
In order for gene to be activated, enzymes must
temporarily break down hydrogen bonds between
bases and detach gene from the histones.
Process of gene activation is not completely
understood.
However, more is known about protein synthesis.
Transcription and translation.
Anatomy and Physiology for Engineers
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Transcription
Genes are found in nucleus but protein synthesis occurs in cytoplasm
(ribosomes); need a messenger (mRNA) to carry blueprint information to
manufacturing site.
Process of creating mRNA is called transcription.
Enzyme (RNA polymerase) binds to the initial segment of activated gene.
RNA polymerase begins replicating nitrogenous bases
Will code Uracil for Thiamine (U for A -- instead of T).
Sequence of 3 bases on RNA ‡ codon: complementary to DNA triplet.
At ‘file end’ signal, RNA polymerase detaches; mRNA strand moves through
nuclear pores.
Anatomy and Physiology for Engineers
Slide 3-45
Translation
Synthesis of proteins using information encoded in mRNA.
Every amino acid has at least 1 unique and specific codon.
Initiated when a newly created mRNA strand binds with a ribosome.
Transfer RNA (tRNA) delivers
amino acids to ribosomes for
assembly of proteins (> 20 types of
tRNA).
1st tRNA with 1 amino acid arrives
and binds to 1st mRNA codon.
2nd tRNA arrives with 2nd amino
acid‡ binds to 2nd codon.
Ribosomal enzymes attach amino
acids 1 and 2 with a peptide bond,
and shifts up 1 codon.
Dipeptide is now attached to amino
acid # 3 arriving on 3rd tRNA.
Continue adding amino acids until
stop codon is reached.
Ribosome detaches.
Anatomy and Physiology for Engineers
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Cell Division and Mitosis
Integral part of growth.
Single cell to 75 X 1012 cells for mature adult.
Occurs via cell reproduction.
Central to reproduction is accurate duplication of cell’s genetic material
into 2 daughter cells ‡ Mitosis.
Mitosis involves division of somatic cells (mature cells).
Production of reproductive cells (sperm and ova) involve different kind of
cell division ‡ meiosis.
Time between cell division ‡ interphase.
Majority of cell life is spent in interphase.
Some cells (nerve, heart, skeletal) never leave interphase.
Preparation for mitosis requires increased production of organelles and
cytosol ‡ may take hours, days, weeks.
Digestive cells divide every few days; cells lining a wound only divide after an
injury.
Once preparations are complete, cell replicates DNA in the nucleus (6 – 8
hours).
Anatomy and Physiology for Engineers
Slide 3-47
DNA Replication
Purpose of DNA replication is to copy genetic information in nucleus.
One set of chromosomes can go to each of the daughter cells.
Process begins when complementary strands separate and unwind.
DNA polymerase (enzyme) bind to exposed nitrogenous base pairs.
Complementary nucleotides in nucleoplasm attach to exposed DNA bases.
Two copies of the DNA molecule are thereby created; mitosis begins
shortly thereafter.
Anatomy and Physiology for Engineers
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Stages of Mitosis
Once duplicated chromosomes are created, need to separate and enclose these into
2 identical nuclei.
Cytokinesis: separation of the cytoplasm to form 2 separate but identical cells.
Mitosis involves:
Prophase:
Chromosomes coil tightly.
Chromatids: chromosome copies; attached at the centromere.
As chromosomes appear, 2 centriole pairs move to opposite poles of the nucleus.
Array of microtubules (spindle fibers) extend between centriole pairs.
Prophase ends with the disappearance of the nuclear envelope.
Metaphase
Spindle fibers enter nuclear region.
Chromatids attach.
Chromatids move to a narrow plane at center of cell (metaphase plate).
Anaphase
Centromere of each chromatid pair splits.
2 daughter chromosomes move to opposite sides of cell.
Telophase
Two nuclear membranes form.
Nuclei enlarge.
Chromosomes uncoil.
Anatomy and Physiology for Engineers
Slide 3-49
Stages of Mitosis
Once duplicated chromosomes are created, need to separate and enclose
these into 2 identical nuclei.
Cytokinesis: separation of the cytoplasm to form 2 separate but identical
cells.
Mitosis involves:
Prophase:
Chromosomes coil tightly.
Chromatids: chromosome copies;
attached at the centromere.
As chromosomes appear, 2
centriole pairs move to opposite
poles of the nucleus.
Array of microtubules (spindle
fibers) extend between centriole
pairs.
Prophase ends with the
disappearance of the nuclear
envelope.
Anatomy and Physiology for Engineers
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Stages of Mitosis
Mitosis involves:
Prophase:
Metaphase
Spindle fibers enter
nuclear region.
Chromatids attach.
Chromatids move
to a narrow plane
at center of cell
(metaphase plate).
Anatomy and Physiology for Engineers
Slide 3-51
Stages of Mitosis
Mitosis involves:
Prophase:
Metaphase
Anaphase
Centromere of
each chromatid
pair splits.
2 daughter
chromosomes
move to opposite
sides of cell.
Anatomy and Physiology for Engineers
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Stages of Mitosis
Mitosis involves:
Prophase:
Metaphase
Anaphase
Telophase
Two nuclear
membranes form.
Nuclei enlarge.
Chromosomes uncoil.
Anatomy and Physiology for Engineers
Slide 3-53
Cytokinesis
Once daughter chromosomes separate, cell
pinches off via constriction of the cytoplasm
along the metaphase plate.
After nuclear membranes are formed, cell
pinches off completely, forming 2 separate
cells.
Completion of cytokinesis forms end of the
process of cell division.
Anatomy and Physiology for Engineers
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Mitosis
Anatomy and Physiology for Engineers
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