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Suzanne D'Anna 1
CELLS AND TISSUES
Cell Parts
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Basic Cell defined as the structural and functional unit of all
living things
- as small as 1/1000th of an inch (bacteria)
- as large as 4 feet (certain nerve cells) Shape:
- disc shaped, thread-like, cube-like, etc. Functions:
- protection, hormones, chemical regulation, gas exchange, cleanse blood
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Main Regions of a Cell
plasma (cell) membrane cytosol (cytoplasm) organelles
- specialized highly organized structures for specific cellular activities
inclusions
- temporary structures
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Plasma (cell) Membrane
outer layer of the cell fragile barrier separates internal components of the
cell from the external environment contains cell contents two lipid layers - protein molecules are
suspended between lipid layers
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Plasma (cell) Membrane (cont.)
unique structure which determines which substances enter or leave the cell
Consists of:
- phopholipids
- cholesterol
- proteins
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Functions of Membrane Proteins
channels enzymes transportation of substances across
membrane receptor sites for hormones,
neurotransmitters, or nutrients cytoskeleton anchors cell identity markers
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Cytoplasm
outside nucleus inside plasma membrane site of most cellular activities Major elements include:
- cytosol
- inclusions
- organelles
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Cytosol
viscous, transparent, gel-like 75% H2O + solid components:
- proteins, carbohydrates, lipids, and inorganic substances - inorganic substances and smaller organic substances soluble in H2O are present as solutes - larger organic compounds are
found as colloids (semi-solid matrix)
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Organelles
little organs specialized structures characteristic appearances specific roles in growth, maintenance,
repair, and control chemically different with one another
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Nucleus
Three distinct components:
- nuclear membrane
- nucleoli
- chromatin
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Nucleus (cont.)
largest organelle in the cell usually oval or spherical - conforms to
shape of the cell contains genetic material (DNA) controls cellular functions directs cellular activities surrounded by nuclear membrane
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Nuclear Membrane
double layer bound to nucleus encloses nucleoplasm in which nucleoli
and chromatin are suspended has large pores
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Nucleoli
little nucleus dense body composed mostly of RNA and protein ribosome production (migrate through
pores in nuclear envelope and enter cytoplasm)
disappear during cell division and reappear in daughter cells
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Chromatin
loosely coiled fibers of DNA and associated proteins
before cell division DNA duplicates, chromatin fibers coil and shorten to form chromatids
one of two spiral filaments joined at the centromere which make a chromosome
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Ribosomes
tiny, round dark bodies sites of protein synthesis contain ribosomal RNA (rRNA)
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Endoplasmic Reticulum system of membrane-enclosed tubules
or channels that coil and twist; called cisterns
continuous with nuclear envelope serves as minicirculatory system provides surface area for chemical
reactions Two types:
- granular and agranular
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Endoplasmic ReticulumGranular
rough studded with ribosomes which synthesize
protein temporary storage area together with Golgi body it synthesizes
and packages molecules that will be excreted from the cell
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Endoplasmic ReticulumAgranular (smooth)
site of fatty acid, phospholipid, and steroid synthesis
inactivates or detoxifies chemicals such as alcohol, pesticides, and carcinogens
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Golgi Apparatus (body or complex)
stacks of flattened sacs with bulges at ends
located close to nucleus modifies, packages, and secretes
proteins and lipids as proteins accumulate in sacs, the sacs
swell; swollen sac pinches off to form vesicles that travel to cell membrane
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Route of Proteins for Export
ribosomes rough ER transport
vesicles Golgi body secretory
vesicles release to exterior of cell
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Lysosomes
membrane-enclosed vesicles formed in Golgi body contain powerful digestive enzymes (as
many as 40) responsible for breaking down molecules
can also digest worn-out cell structures (autophagy) and foreign substances
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Peroxisomes
membrane sacs similar to lysosomes but smaller
contain enzymes that use molecular oxygen to oxidize organic substances
detoxify potentially harmful substances that may enter the bloodstream (e.g., free radicals)
especially important in liver and kidneys
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Mitochondria(powerhouse of the cell)
sausage-shaped fluid filled sacs double membrane wall outer wall is smooth inner wall - series of folds called cristae cristae provide surface area for cellular
respiration (only occurs if O2 is present) enzymes on cristae catalyze reactions that
generate ATP
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Cytoskeleton
responsible for cell movement and for movement of organelles and chemicals within the cell
Network of protein structures:
- microfilaments
- microtubules
- intermediate filaments
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Microfilaments
rod-like structures formed from the protein actin in muscle tissue - actin filaments (thin)
and myosin (thick) slide past one another to produce contraction
in non-muscle - actin filaments support and shape
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Microtubules
larger than microfilaments straight, slender cylindrical structures -
contain the protein tubulin support and shape cells movement of substances
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Intermediate Filaments
medium size strong and tough provide structural reinforcement
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Centrosome
cytoplasmic material within centrosome is pair a of rod-shaped
bodies called centrioles
- lie at right angles to each other
- during cell division, centrioles direct formation of mitotic spindle
- like mitochondria, they contain DNA and control self replication
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Cilia
minute projection extending from cell surface
contain ten pairs of microtubules act to move substances along cell surface beat rhythmically to move fluids or
particles over cell surface
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Flagella
long whip-like projections extending from free cell surface
act to propel a cell contain ten pairs of microtubules tail of sperm is a flagellum
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