Download (nucleus, cytosol, organelles, membrane) and their basic functions

Chapter 3 Lecture Outline
page 1
I. cell structure
 cells consist of cytoplasm surrounded by the cell membrane
 the cytoplasm consists of cytosol plus organelles
 each cell has a nucleus* that is located somewhere inside the cell
*red blood cells eject their nuclei before entering the blood
A. membrane structure
1. lipid bilayer
a. phospholipids
each molecule has a hydrophilic “head” and a
hydrophobic “tail”
they automatically arrange themselves in a double layer
so the tails are always inside
BIOL 2404
Strong/Fall 2006
Chapter 3 Lecture Outline
page 2
b. cholesterol molecules among the tails keep the membrane
flexible and stable
2. proteins sit between the phospholipid molecules
a. receptors
b. channels
c. carriers
d. enzymes
e. anchors
f. recognition
3. carbohydrates are attached to the outer surface of phospholipids
and proteins
a. adhesives
b. recognition
B. cytosol is the same as intracellular fluid (ICF)
 slightly viscous
 water, ions, proteins, carbohydrates, amino acids, lipids
BIOL 2404
Strong/Fall 2006
Chapter 3 Lecture Outline
page 3
C. organelles are intracellular structures that perform specific functions
1. cytoskeleton - protein fibers for shape, attachment, movement,
intracellular transport
2. microvilli - short finger-like extensions of cell membrane supported
by microtubules that increase the cell’s surface area
3. centrioles used in cell division
4. cilia - long hair-like extensions of the cell membrane supported by
microtubules that move materials across the cell’s surface
5. flagellum - very long hair-like extension of the cell membrane
supported by microtubules that moves the cell
6. ribosomes - small structures made of protein and RNA that are
either in the cytosol or attached to the endoplasmic reticulum
 they read RNA molecules that are copies of parts of the DNA
in the nucleus, and use the information to make proteins
7. endoplasmic reticulum (ER) - network of connected membrane
tubes attached to the nuclear envelope
a. smooth ER (SER) has no ribosomes makes lipids and
carbohydrates for all membranes
 makes steroids
 makes and stores glycogen
b. rough ER (RER) has ribosomes on its surface
 makes proteins
 both SER and RER deliver molecules to the Golgi apparatus
BIOL 2404
Strong/Fall 2006
Chapter 3 Lecture Outline
page 4
8. Golgi apparatus - stack of flattened membrane discs that
a. make and package secretions
b. make new membranes
c. package enzymes for intracellular use
9. lysosomes - hydrolytic enzymes enclosed in a membrane
 break down and recycle old cell parts
 kill engulfed pathogens
10. peroxisomes - enzymes enclosed in a membrane
 break down some organic molecules
 produce hydrogen peroxide (a free radical)
11. mitochondria
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double membrane
inner membrane has wrinkles called cristae
fluid inside inner membrane is matrix
enzymes in matrix and cristae break down fuel molecules to
make ATP
this process requires oxygen to get rid of the byproducts
(aerobic)
mitochondria contain DNA that is different from nuclear DNA
mitochondria are inherited from the maternal parent
they replicate themselves
the number of mitochondria in a cell depends on the cell’s
energy needs
D. nucleus
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usually one per cell
stores DNA (genetic information)
surrounded by a double membrane with pores (nuclear envelope)
human DNA occurs in long molecules called chromosomes
all cells except eggs and sperm have 46 chromosomes (2 sets of 23
chromosomes each)
BIOL 2404
Strong/Fall 2006
Chapter 3 Lecture Outline
page 5
II. functions of the cell membrane
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separates ICF and extracellular fluid (ECF)
controls movement into and out of the cell
responds to signals from outside the cell
attaches cells together in some tissues
A. transport through the cell membrane
1. permeability determines which molecules can pass through a
membrane
 cell membranes are selectively permeable, allowing some
things to pass in or out but not others
 factors that affect the ability of a molecule to pass though a
membrane are:
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size:
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lipid solubility:
(molecules that are polar or have an electrical charge have low
lipid solubility)
2. energy is required for all forms of transport
a. kinetic energy (diffusion)
b. ATP (active transport, vesicular transport)
3. diffusion
a. physical basis
 molecules move and collide randomly
 the amount of movement depends on their level of kinetic
energy
 the level of kinetic energy depends on the temperature
 eventually, molecules become evenly distributed
BIOL 2404
Strong/Fall 2006
Chapter 3 Lecture Outline
page 6
b. definition
 random motion makes it look like molecules are moving from
where their concentration is higher to where their concentration
is lower
c.
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diffusion can occur
inside the cell (in the ICF)
outside the cell (in the ECF)
across the cell membrane
o through the lipid bilayer
o through channels
d. osmosis is the diffusion of water through a cell membrane
 it appears as if water moves towards the side of the membrane
with the higher solute concentration
 assume the solutes have a force that attracts water
 this force is called osmotic pressure
 the higher the solute concentration of a solution, the higher its
osmotic pressure
BIOL 2404
Strong/Fall 2006
Chapter 3 Lecture Outline
page 7
 when a cell is in a solution with the same solute concentration (solute
concentration of ICF = solute concentration of ECF):
 osmotic pressure is equal on both sides of the membrane
 no net movement of water through the membrane
 when a cell is in a solution with a lower solute concentration (solute
concentration of ICF < solute concentration of ECF):
 osmotic pressure is higher in the ICF
 net movement of water into the cell
 when a cell is in a solution with a higher solute concentration (solute
concentration of ICF > solute concentration of ECF):
 osmotic pressure is higher in the ECF
 net movement of water out of the cell
BIOL 2404
Strong/Fall 2006
Chapter 3 Lecture Outline
page 8
4. carrier mediated transport
 specific membrane proteins assist molecules through the
membrane
 carriers are specific
 carriers may take more than one molecule or more than one type
of molecule per trip
 carriers may move molecules in opposite directions
a.
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facilitated diffusion is required when:
molecule is going down its concentration gradient but
is too large to fit through channels
is not lipid soluble enough to go through the lipid bilayer
b. active transport is required when molecules must be moved
against their concentration gradient
 example: Na/K-ATPase (sodium-potassium pump)
5. vesicular transport
 involves small membrane sacs
 is required when large molecules or large volumes must be moved
across the cell membrane
a. endocytosis
 molecules to be moved into cell are surrounded by cell membrane
to form vesicle inside cell
 vesicle separates from membrane
BIOL 2404
Strong/Fall 2006
Chapter 3 Lecture Outline
page 9
examples:
phagocytosis – bacteria, dead cells
pinocytosis – drops of ECF
b. exocytosis
 molecules to be moved out of cell are packaged into a vesicle
 the vesicle joins the inside of the cell membrane and opens to the
outside, releasing its contents
 also use to add more cell membrane
B. membrane potentials
 a combination of channels and carriers in the cell membranes of resting
cells maintains an unequal and opposite distribution of ions and
electrical charges on the inside and outside surface of the cell
membrane
 this is a form of potential energy
BIOL 2404
Strong/Fall 2006