Transcript Structure

Unit 1.2: Cells and Transport Processes
I. Three Main Components of a Cell:
A. Cell Membrane:
1. Structure: a phospholipid bilayer
a. 2 layers of lipid tails “sandwiched” between phosphate heads
b. Lipid tails are hydrophobic; no water in the middle of the
“sandwich” so they are “protected”
c. Phosphate heads are hydrophilic; can interact with water
2
2. Functions:
a. Provides structure to the cell
b. Controls what enters and exits the
cell: “selectively permeable”
1) Lets some things in, keeps others
out
2) Materials that need to get into or
out of the cell pass through
protein channels:
a) Peripheral: on one side or the other;
for cell recognition and communication
b) Integral: go all the way thru; like
“tunnels”, but specific to certain
molecules
3) Fluid Mosaic Model: phospholipids
and proteins move around in the
membrane, are not stuck in one
place
3
B. Nucleus:
1. Structure:
a. Phospholipid bilayer: like the
cell membrane
b. Nuclear pores: allow materials
to move into and out of nucleus
1) Like the “protein channels” in the
cell membrane
2. Functions:
a. Stores DNA:
1) As chromatin to make proteins
2) As chromosomes during mitosis
b. Contains nucleolus:
1) Makes ribosomes that migrate to
cytoplasm through nuclear pores
4
C. Cytoplasm:
1. Structure: gel-like material;
contains cytosol, cytoskeleton
and organelles
a. Cytosol: fluid composed of water,
dissolved salts, minerals, etc…
b. Cytoskeleton: filaments that
provide framework, allow
movement of materials in the cell
• Actin, tubulin
2. Function:
a. Maintains shape of cell
b. Provides suspension of organelles
5
II. Organelles:
A. Endoplasmic Reticulum (ER)
1. Structure: interconnected “cisterns/sacs”
a. Can be rough or smooth
1) Rough if ribosomes are attached: in cells that export proteins
2) Smooth if no ribosomes attached: in cells that detoxify substances
2. Function: to transport proteins
a. Like a highway system or the circulatory system
6
B. Ribosome:
1. Structure: two subunits made
of RNA and protein
2. Function: to make proteins
a. Binds amino acids together
according the DNA coded into
mRNA
C. Golgi Apparatus:
1. Structure: flattened sacs of ER
a. like a portion of ER that has
“budded off”
2. Function: to modify proteins
for export
a. “tags” them with molecules to
direct where they will be
“delivered”
7
D. Mitochondria:
1. Structure: rod-shaped, double-membrane
a.
Inner membrane (cristae) is highly folded, more
surface area = more reactions.
2. Function: converts food into energy – respiration
• C6H12O6 + O2CO2 + H2O + ATP
E. Lysosome:
1.
2.
Structure: phospholipid bilayer surrounding
hydrolytic enzymes
Function: Stores enzymes that break down food,
old organelles, viruses/bacteria
F. Vesicles:
1. Structure: phospholipid bilayer “sac” that pinches
off from cell membrane
2. Function: to transport material into or out of cell
8
G. Cytoskeleton:
1. Structure: made of microfilaments
and microtubules
a. Microfilaments: actin protein
b. Microtubules: tubulin protein
2. Function: to provide structure,
movement
H. Centrosome: (centrioles)
1. Structure: two hollow cylinders
made of microtubules
a. Each arranged in 9 groups of 3
b. At right angles to each other
2. Function: form mitotic spindle to
move chromosomes during mitosis
9
I. Cilia and Flagella:
1. Structure: both made of tubulin
proteins in a “9+2” arrangement
a. Cilia: many, short fibers
b. Flagella: a single, long fiber
c. “Dynein” protein provides motive
power
2. Function: both used for movement
a. Cilia: move materials over cell surface
with back-and-forth motion
1)
Ex: cilia line bronchioles in your throat,
helps to filter dust
b. Flagella: moves the entire cell using
propeller-like motion
1)
Sperm are the only flagellated human
cells
10
III.Transport Across Membranes:
A. Direction of movement depends on “concentration
gradient” Next time: define
B. Moving down
(with) the gradient
means the substance
Concentration
Gradient
moves from an area with more to an area with less of the
same substance.
1. Moves until both areas have same amount of substance
2. Like a truck moving downhill, from more height less height;
doesn’t require energy
11
C. Moving up (against) the gradient means the substance
moves from an area with less of that substance to an area
with more of that same substance
1. “Balance” cannot be achieved
2. Like a truck moving uphill from low height  more height;
requires energy!
12
Transport Across Cell Membranes
Passive Transport – no energy required
Active Transport – requires energy
Membrane
Pumps
Ex: Na+/K+
pump
Osmosis:
water
Diffusion:
substances
Facilitated
Diffusion
Endocytosis: takes
substance into cell
Pinocytosis
Liquids in
“drinking”
Ion Channels
Phagocytosis:
solids in
“eating”
Exocytosis:
substances exit
cell
13
IV. Passive Transport: no energy needed
A. Osmosis: Movement of water from area with
more  area with less (down its gradient)
B. Diffusion: movement of a substance from area
with more  area with less (down its gradient)
14
C. Comparing Solute Concentrations:
1. Hypertonic: outside solution has more salt
than the cell
a. Hypertonic: more salts = less water
b. Less water outside cell = more water in cell, so…
water will flow out of the cell
1) Animal cells will shrink - crenation
2. Hypotonic: outside solution has less salt than
the cell
a. Hypotonic: less salts = more water
b. More water outside cell = less water in cell, so…
water will flow into the cell
a. Animal cell will burst - plasmolysis
3. Isotonic: same amount of “salts” in both
solutions, so no “net” movement
15
D. Diffusion across cell membrane:
1. Nonpolar substances “dissolve” directly through:
a. “Like dissolves like”: Lipid tails of membrane are nonpolar, so
small, nonpolar molecules pass through membrane quickly
1) Ex: CO2, O2
b. Some small, polar molecules also dissolve through, but slower.
1) Ex: H2O, urea
16
2. Facilitated Diffusion: “facilitate” = help
a. Carrier proteins (“tunnels”) allow large
molecules to travel across membrane.
1) Carrier proteins are specific for molecule:
glucose protein will not transport amino
acids
2) No ATP needed b/c moving down its
gradient
b.
Ion channels allow charged atoms
(ions) to travel through.
1) Ex: Na+, Ca2+, Cl2) Ion channels are also specific for each ion.
a)
Ex: Na+ channel will not transport Ca2+
17
V. Active Transport – Requires energy!
A. Materials move from area with
less
into area with more
1. Against the gradient, up the hill
B. Membrane Pumps
1. Carrier proteins, ion channels can
also be used for active transport
2. Sodium-Potassium Pump
a. Exchanges 3 Na+ for 2 K+
b. **ATP required to change shape of
carrier protein
c. For transmitting nerve impulses
18
C. Exocytosis: substance “exits”
cell
1. Ex: proteins for export, waste,
toxins, etc…
2. Vesicle containing material
fuses with cell membrane,
releasing contents to outside
D. Endocytosis: substances
taken “into” cell
1. External material enclosed in
vesicle
2. Two types of endocytosis:
a. Pinocytosis: cell takes in liquid;
“drinking”
b. Phagocytosis: cell takes in
solids; “eating”
19
Warm-up answers for this unit:
20