Cell Structure and Function
I. Cells
A. Size and shape
1. All cells are microscopic
2. Human cells vary widely in size (rbc = 7.5 um, ovum = slightly less than 1
mm.
3. Differ in shape: flat, cuboidal, rectangular, round, disk shaped, threadlike, spindle, etc.
B. Composition
1. Cytoplasm with organelles surrounded by a plasma membrane
2. Three main parts are:
a. Plasma membrane – surrounds entire cell
b. Cytoplasm – all “living matter” inside the cell except the nucleus;
cell water + organelles
c. Nucleus- membrane bound, contains genetic information
C. Relationship of cell structure and function
1. Every cell does certain things to maintain it’s own survival
2. Every cell does things to insure survival of the body, but these functions
differ from cell type to cell type:
3. Relationship of structure to function apparent in number and type of
organelles seen in different cells
a. Cardiac cells – mitchondria
b. Sperm cells - flagella
II. Structural parts
A. Plasma membrane
1. Double-layered membrane of phospholipids containing proteins and
cholesterol, 7-8 nm in diameter
2. Integral and peripheral proteins
3. Receptors and signals, tissue antigens
4. Selectively permeable
B. Nucleus
1. Nuclear envelope
a. Double membrane, surrounds nucleoplasm
2. Nucleoplasm like cytoplasm, contains:
a. Nucleolus
(1) Programs formation of ribosomes in nucleus
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(2) Ribosomes then migrate through nuclear envelope to
cytoplasm
b. Chromatin granules
(1) DNA
(2) Chromosomes – tightly coiled DNA
(3) Histones – proteins that DNA is wrapped around
C. Cytoplasm
1. Cytosol
2. Organelles
a. Ribosomes
(1) May attach to rough ER or lie free in cytoplasm
(2) Manufacture proteins
(3) Often called protein factories
b. Endoplasmic reticulum
(1) Network of connecting sacs and canals, from nucleus almost
to cell membrane
(2) Rough and smooth
(3) RER collects and transports proteins made by ribosomes
(4) SER has enzymes associated to make lipids; cholesterol,
lipoproteins, phospholipids
(5) Vesicles bud off and transport products to Golgi for
processing and packaging
c. Peroxisomes
(1) Enzymes to breakdown hydrogen peroxide, alcohol,
formaldehyde
d. Golgi apparatus
(1) Stacks of flattened sacs near the nucleus
(2) Transport vesicles from ER fuse with cis face
(3) Products are modified and concentrated as they move from
“plate” to “plate”
(4) Vesicles bud off trans face and move to plasma membrane;
fuse and are relased to outside of cell
e. Mitochondria
(1) Powerhouse of the cell – ATP from cellular respiration
(2) Double membrane, inner highly convoluted
(3) Folds contain enzymes for cellular respiration
f. Lysosomes
(1) Digestive bags – stomachs of the cell
(2) Membranous sacs with hydrolytic enzymes
(3) Digest worn out cell proteins, phagocytized material
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(4) If membrane ruptures contents digest cell – sucide bags
g. Centrioles
(1) Paired
(2) Lie at right angles to each other
(3) Composed of tubules, rod or barrel shaped
(4) Function in cellular reproduction
(5) Found near the nucleus in the MOC
h. Cilia
(1) Fine hairlike extensions on surface of some cells
(2) Move in wave like fashion to move substances over the
surface fo the cell
i. Flagella
(1) Single projection extends from surface of cell
(2) Much larger than cilia
(3) Moves in whiplike fashion to propel cell
(4) In humans only sperm have flagella (tail)
III. Plasma Membrane Transport
A. Passive transport process
1. Diffusion – movement from an area of high to low concentration
2. Osmosis – water through a semipermeable membrane
3. Dialysis – solutes across the selectively permeable membrane
4. Filtration – hydrostatic pressure
B. Active transport process
1. Require energy (ATP) – push against a concentration gradient
2. Ion pumps
a. Move specific ions across the cell membrane against their
concentration gradient
b. May be coupled to other ion pumps; sodium/potassium pump
c. May also be coupled to transport proteins that act as carriers to get
large lipid-insoluble substances into the cell
3. Phagocytosis and pinocytosis
a. Cell eating and drinking
b. Engulf particles; phagocytosis for large insoluble particles,
pinocytosis for small dissolved substances
4. Exocytosis – extrude substances to exterior, secretion
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IV. Cell Division
A. DNA structure
1. Nucleotides
a. Nitrogenous bases
b. Pentose sugars (deoxyribose)
c. Phosphate group
2. Complementary base pairing
3. Genes
4. Humans have >3 billion base pairs, about 30,000 genes
5. Double helix, coiled, antiparallel
B. Genetic code
1. The information stored in each gene
2. Specifies enzyme and other protein structure
3. Enzymes facilitate cellular chemical rxns – cellular chemical rxns
determine cell structure and function
C. RNA and protein synthesis
1. mRNA, rRNA, tRNA
2. Transcription
3. Translation
D. Mitosis and cytokinesis
1. Interphase – “resting”; DNA replicated
2. DNA replication
a. Uncoils and separates
b. Complementary bases attached to strands
c. Semi-conservative replication
E. Mitosis
1. Prophase
a. Chromatin condenses into visible chromosomes
b. Chromatids (copies of chromosomes) become attached at the
centromere
c. Spindle fibers appear
d. Nucleolus and nuclear envelope disappear
2. Metaphase
a. Spindle fibers attach to each chromatid
b. Chromosomes align across the center of the cell
3. Anaphase
a. Centromeres break apart
b. Chromosomes move away from the center of the cell
c. The cleavage furrow appears
4. Telophase
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a. The nuclear envelope and both nuclei appear
b. Cytoplasm and organelles divide equally
c. Process of cell division is completed
5. Results of mitosis
a. Identical daughter cells
b. In adults mitosis replaces worn out or damaged cells
c. During growth allows tissues to develop
d. Loss of control of mitosis results in growth of an abnormal mass of
cells – neoplasm
(1) Benign
(2) Malignant
F. Meiosis
1. Cell division used to produce sperm and eggs (oogenesis in females and
spermatogenesis in males)
2. Chromosome number is reduced from 46 to 23 – so when the sperm and
egg unite, eureka, you get 46 chromosomes in the fertilized egg!
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