Download THE CELL

AP Biology-Chapter 7
Pages 108-135
THE CELL
I.
II.
Overview
A. prokaryotic vs. eukaryotic
1. both contain a plasma membrane, cytosol (semifluid), chromosomes, and ribosomes
2. difference is the presence of membrane-bound organelles including a nucleus
a) prokaryotes concentrate the DNA in a region called the nucleoid
3. eukaryotes are larger
B. plant vs. animal cells
1. Figures 7.7 and 7.8 on pages 114-115
2. Animal-no cell wall, chloroplast, central vacuole (with tonoplast), or plasmodesmata
3. Plant-no lysosomes, centrioles, flagella
Structure
A. Nucleus
1. contains most of the genes of a eukaryote (some in mitochondria and chloroplasts)
2. nuclear envelope is a double membrane
a) nuclear pores are kept open by a protein structure called the pore complex
b) nuclear lamina-netlike protein filaments lining the nuclear side of the envelope
c) nuclear matrix-evidence for a framework of fibers throughout the nuclear
interior
3. chromatin-DNA and proteins
a) condense into individual chromosomes during cell division
4. nucleolus-dense fibers and granules adjoining part of the chromatin
a) does not have a membrane
b) synthesizes ribosomal RNA (rRNA) which combines with proteins from the
cytoplasm to form the two subunits of a ribosome
B. Ribosome
1. made of rRNA and proteins
2. two subunits that join during protein synthesis
3. cells with high rates of protein synthesis have larger numbers of ribosomes
4. free and attached (structurally identical and can switch places)
a) free (not bound to the ER)-often produce proteins needed within the cytosol
b) attached (connected to the ER)-produce proteins for insertion into membranes
or for secretion from the cell (i.e. digestive enzymes)
C. Endoplasmic Reticulum
1. network of membranous tubules and cisternae (sacs)
2. accounts for more than 50% of the total membrane of a cell
3. connected directly to the nuclear envelope (Figure 7.11 page 119)
4. smooth ER
a) responsible for synthesis of lipids, metabolism of carbohydrates, and
detoxification of drugs and poisons
b) important steroids-sex hormones of vertebrates, hormones from adrenal glands
c) detoxify by adding hydroxyl groups to drugs (makes more soluble for excretion)
d) in muscles, ER pumps Ca2+ into cisternal space; Ca2+ moves back during a
contraction
5. rough ER
a) attaches carbohydrates to proteins to form glycoproteins (most secretory
proteins are glycoproteins)
b) leave ER in bubble-like buds of membrane called transport vesicles
c) also produces more membrane
D. Golgi apparatus
1. center for manufacturing, warehousing, sorting, and shipping
2. modifies products of the ER and sends to other destinations
3. made of flattened membrane stacks called cisternae
4. has distinct ends
a) cis face: receiving end (usually located near the ER)
b) trans face: shipping end
5. manufactures polysaccharides including non-cellulose polysaccharides (pectin)
6. adds molecular ID tags during modification to aid in shipping
E. lysosomes
1. membrane-bounded sac filled with hydrolytic enzymes that digest macromolecules
(all classes)
2. maintains a pH near 5
3. enzymes and membrane are made by the ER
4. may digest particles from phagocytosis
5. recycle a cell’s own organic material called autocytosis
6. cellular self-destruction may occur by lysosomes (tadpole tail, webbed digits)
F. vacuoles
1. large membrane-bounded sacs
2. various functions
a) food vacuoles: formed from phagocytosis
b) contractile vacuoles: pump excess water out of the cell (in protists)
c) central vacuole: found in mature plant cells
1) store inorganic ions
2) disposal site for metabolic by-products
3) water storage
G. mitochondria
1. site of cellular respiration
2. contain their own DNA
3. enclosed by two membranes
a) outer membrane is smooth
b) inner membrane is in folds called cristae
c) mitochondrial matrix: enclosed by inner membrane
d) intermembrane space: between outer and inner membranes
H. chloroplasts
1. specialized plastid (plant organelles)
2. double membrane outer layer
3. another membrane system is inside the cholorplast
a) thylakoids: flattened stacks of membrane
b) granum: stack of thylakoids
c) stroma: fluid outside the thylakoids (contains enzymes, ribosomes, and DNA)
d) thylakoid space: inside the thylakoids
I. peroxisome
1. single membrane compartment
2. transfer hydrogen to oxygen and create H2O2 as a by-product
3. functions include: detoxify alcohol in the liver, break fatty acids into smaller
molecules
4. a second enzyme converts the H2O2 to water
J. cytoskeleton
1. network of fibers extending throughout the cytoplasm
2. gives mechanical support and maintains shape
3. involved in cell motility (within the cell and cell location)
4. three main types of fibers
a) microtubules (largest)
1) hollow tube constructed of a globular protein called tubulin
2) shape and support cell
3) provide tracks for shipping organelles
4) separate chromosomes during cell division
5) may grow from the centrosome (a region of the cell near the nucleus)
6) responsible for movement of cilia and flagella
a. core of microtubules encased by plasma membrane
b. 9+2 arrangement (nine doubles surrounding two singles)
c. anchored to the cell by a basal body (identical to a centriole)
d. dynein-protein that connects microtubules to each other
b) microfilaments (smallest)
1) made of the globular protein actin (also called actin filaments)
2) solid rod made of a twisted double chain of actin
3) bear tension forces (pulling)
4) combine with the protein myosin for muscle contraction (shorten cells)
Fig 7.27 p. 131
5) also produce pseudopods for amoeboid movement
6) may be involved in cytoplasmic streaming in plant cells
c) intermediate filaments
1) sized between microfilaments and microtubules
2) bear tension forces
3) constructed of keratin proteins
4) especially important for shape of cell and for fixing the position of certain
organelles (i.e.-nucleus)
K. Cell wall
1. protects, maintains shape, prevents excess uptake of water
2. chemical composition varies from species to species
3. basic design is similar
a) primary cell wall-thin and flexible; secreted by young plants
b) middle lamella-space between cell walls; contains the sticky protein pectin that
glues cells together
c) secondary cell wall-deposited in layers in mature plants
L. Extracellular matrix
1. outside the cell
2. made of glycoproteins
a) collagen-strong fiber network
b) proteoglycan-protein rich in carbohydrates
c) fibronectin-serves as an anchor for collagen and proteoglycan; attaches to
integrin
d) integrin-protein embedded in the plasma membrane
e) Figure 7.29 on p. 133
M. Intercellular junction
1. direct contact between cells
a) plasmodesmata-openings in cell walls that allows cytosol to move between cells
in plants
b) tight junction-membranes of neighboring animal cells are fused together
c) desmosomes (anchoring junctions)-act like rivets to fasten cells into sheets
d) gap junctions (communication junctions)-provide channels between cells that
allow ions, sugars and amino acids to pass through