Chapter 3 – The Cellular Level of Organization
Generalized cell
 All eukaryotes are composed of three main parts:
o Plasma membrane: outer boundary; movement in and out of cell; flexibility.
o Cytoplasm: all structures and fluid found inside the cell excluding NUCLEUS
o Nucleus: contains DNA/RNA
Plasma membrane
- Responds to changes in internal and external membrane
The Plasma Membrane
- Bilayer of phospholipids and proteins
- FUILD MOSEIC MODEL – has flexibility, isn’t rigid
- Phospholipids move around
- Proteins help decide what comes in and out, they change; we put in new proteins, take out old ones
- Proteins act as “gatekeepers”
- Sugars and carbohydrates
THE STRUCTURE OF THE MEMBRANE – lipds
75% Phospholipids
Hydrophilic phosphate heads face water
Hydrophobic fatty acid tails are hidden from water
THE STRUCTURE OF THE MEMBRANE – proteins
2 types:
1. Integral – (proteins inside cell) they help move things across plasma membrane since they are through
bilayer
2. Peripheral – (proteins outside cell) help with communication, help link cells together
THE STRUCTURE OF THE MEMBRANE – (other proteins)
Glycocalyx:
- Strengthen cell surface (RBC)
o ATTRACTS FILM AND HELPS CELLS MOVE
- Attaches cells together (this is why sugars are sticky)
- cell-cell recognition (“SELF”)
SIX FUNCTIONS OF MEMBRANE PROTEINS
1. ION CHANNELS – selectively move substances across membrane
a. Na, Ca, K
2. TRANSPORTERS – bring substance into or out of cell
a. Glucose,
3. CELL-CELL RECOGNITION
4. RECEPTORS – sends info inside cell. Cell is likely going to bring about a change
a. Ex. Insulin release, cell recognizes this and produces more glucose cells
5. LINKERS – link cells together, link components of plasma membrane together
6. ENZYMES – carry out a change in a substance at the surface of the cell
a. Ex. Breaking down carbohydrates into sugars. Enzyme breaks down lactose molecules into
glucose
MEMBRANE PERMEABILITY:
Impermeable state: nothing allowed into cell
Permeable state: lets anything in
Selectively permeability: select things that come into and out of cell
- Molecular properties enhance membrane permeability
1. LIPID SOLUBILITY OF MOLECULE
a. high lipid solubility – move easily into cell
b. Low solubility (water soluble) – does not move easily into cell
2. MOLECULAR SIZE
MEMBRANE TRANSPORT
- EXCEPTION: water is highly polar and freely permeable
- Large, charged, water soluble things need help to go into cell
TYPES OF MEMBRANE TRANSPORT
1. PASSIVE – NO ENERGY (ATP)
2. ACTIVE – ENERGY (ATP)
PASSIVE PROCESS
- Things move down concentration gradient
- Diffusion of water: osmosis
1.
-
DIFFUSION
No energy required
Things move down its concentration gradient
It is affected by:
o Amount of substance
o Steepness of concentration gradient
o Temperature
2. FACILITATED DIFFUSION
a. Carrier mediated
i. Changes shape, Carry substance across plasma membrane
b. Channel mediated
i. Triggers cause gate to open or close
3. OSMOSIS
a. Movement of water
b. Water has a channel called a pore, where it can freely move across plasma membrane
(AQUAPORIN)
ACTIVE PROCESSES
1. Active transport
a. Primary active transport
i. Energy from ATP hydrolysis
b. Secondary Active Transport
i. Energy from primary transport
PRIMARY ACTIVE TRANSPORT
- Move things against concentration gradient
-
Ex. Sodium potassium pump
o Carrier pump called NA+-K+ ATPase
o Located in all plasma membranes
o Works as an antiporter (things move in opposite directions
o Pumps against Na and K gradient
 NA+ high outside cell pumps 3 out
 K+ high inside cell pumps 2 in
o Maintains electrochemical gradient
SECONDARY ACTIVE TRANSPORT
- Antiporter -carry two substances across the membrane in opposite directions
- Symporters: carry two substances across the membrane in the same direction
TRANSPORT IN VESICLES
Blank: membrane sacs
EXOCYTOSIS:
ENDOCYTOSIS
- Phagocytosis
o Cell eating
o atp
- Pinocytosis
o Cell drinking
THE MEMBRANE POTENTIAL
- A living resting cell has a polar plasma membrane
- Inside
o Inside: excess of negative charge
o Outside: excess of positive charge
Membrane potential – when there is a difference in charge outside and inside cell
Which way would positive ions want to move?
- Inside
Which way would negative ions want to move?
- Outside
Potassium channels are leakier than sodium channels
- This maintains membrane potential
2. CYTOPLASM
Cytosol is NOT the same as cytoplasm
- Chemical rxns take place here (glycolysis)
Organelles
3. Nucleus
- Large organelle
- Contains genes
WRAP UP
Apoptosis – planned programed cell death
Necrosis – cell death due to injury