Download 1 Unit Two: Cells, Cell Structures and Functions I

Unit Two: Cells, Cell Structures and Functions
I. Cell Anatomy
A. Nucleus
1. contents
chromatin
DNA + protein
condenses as visible chromosomes
a) nucleolus
site of RNA synthesis
mass of RNA + protein
b) RNA
produced during transcription
c) proteins (ex: enzymes)
associated with chromatin
necessary for transcription
d) nucleoplasm
semi-fluid medium
cytoplasm-like
2. surrounded by nuclear membrane (nuclear envelope)
a) double membrane
i. inner membrane
defines nucleus
innersurface lined with nuclear lamina
ii. outer membrane
is continuous with rough endoplasmic reticulum (RER)
outer surface covered with ribosomes
iii. lumen
space between membranes
continuous with lumen of RER
b) nuclear pores in nuclear membrane
pores lined with nuclear pore complex which controls the entry and exit
of molecules through pores
B. Ribosomes
site of protein synthesis
composed of small and large subunits of RNA + protein
1. cytoplasmic (“free”) ribosomes
make proteins incorporated into:
a) cytoskeleton
b) mitochondria
c) peroxisomes
2. bound ribosomes
attached to exterior surface of RER
make proteins that are
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a) incorporated into the membrane
b) transported inside organelles
c) transported outside of cell
C. The Endomembrane System
cell components with interchangeable membranes
substances transported between members of system remain isolated from cytosol
1. endoplasmic reticulum (ER)
network of internal membranes
interconnected tubules and cisternae
continuous with nuclear membrane
inner space called lumen
a) smooth ER (SER)
functions:
i. lipid synthesis
ii. carbohydrate metabolism
iii. detoxification
b) rough ER (RER)
with attached ribosomes on exterior surface
functions:
i. synthesis of proteins to be secreted
proteins synthesized into lumen
ii. membrane production
membrane made within RER
membrane proteins made by ribosomes then incorporated
into membrane
new membrane segments transported as vesicles
2. Golgi complex (Golgi) (Golgi apparatus)
made of flattened, stacked membrane sacs called cisternae
modifies protein w/in transport vesicles
transport vesicles fuse with cis face of Golgi
vesicle contents pass through series of cisternae
vesicle containing completed protein pinches off from trans face of Golgi
3. lysosomes
membrane-bound sac of enzymes used for intracellular digestion
a) contents
i. with internal pH of about 4.8
ii. hydrolytic enzymes
functional at acid pH
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split organic compounds
examples: RNase, DNase, phosphatase, protease
b) functions
i. intracellular digestion
ii. recycle organelles
iii. programmed cell destruction – autolysis
regression
removal of damaged cells
iv. destroy bacteria
4. vesicles
small membrane-bound sac
transports between components of endomembrane system
D. Vacuoles and Peroxisomes
1. vacuoles
membrane-bound sac, larger than vesicles
a) food vacuoles
formed by phagocytosis
site of intracellular digestion
fuse with lysosomes
b) contractile vacuoles
pump excess water out of cell
c) central vacuole
in most mature plant cells
surrounded by tonoplast membrane
storage site of:
ions, organic products, wastes, some pigments, poisons, water
2. peroxisomes
single-membrane-bound organelles
a) contain enzymes
i. oxidases – transfer H to oxygen
ii. catalase converts H2O2 to water
iii. others
b) functions of some peroxisome enzymes
i. breakdown fatty acids and amino acids into smaller molecules
that will be used for cellular respiration
ii. detoxification of alcohol and other compounds
iii. specialized peroxisomes in plants (glyoxysomes) convert lipid
to carbohydrate in seeds – used when seeds germinate
E. Mitochondria
site of cellular respiration
semi-autonomous
can grow and reproduce
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possess DNA
possess ribosomes
surrounded by double membrane
F. Plastids
semi-autonomous
membrane not made from ER
found in plants and algae
surrounded by double membrane
contain thylakoid membrane system
exist in a variety of shapes
3 basic types of plastid – based on pigmentation – interchangeable
1. chromoplasts
with yellow and orange pigments (carotenoids)
2. leucoplasts
non-pigmented
usually found in plant parts not exposed to light
a) amyloplasts – store starch
b) proteinplasts – store protein
c) elaioplasts – store oils
3. chloroplasts
with chlorophyll (green)
site of photosynthesis
occur in all green plant parts
thylakoids form grana
G. The Cytoskeleton
network of fibers
fiber types:
1. microtubules
a) structure
hollow rods of tubulin dimers
25 nm diameter
easily disassemble and re-assemble
in cytoplasm of all eukaryotes
b) functions
shape and support cell
intracellular transport
chromosome division
motion of cilia and flagella
2. actin filaments (formerly called microfilaments)
a) structure
solid rods of actin units in a twisted double chain
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7 nm diameter
easily disassemble and re-assemble
b) functions
support
muscle contraction
cytokinesis of animal cell
amoeboid movement
cytoplasmic streaming (plant cells)
3. intermediate filaments
a) structure
composition varies
8-10 nm diameter
stable – do not breakdown
b) functions
cell shape and support
fix position of organelles
nuclear lamina
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