What is the structure of the plasma membrane?
composed of phospholipids
How are phospholipids arranged in the plasma membrane?
Where are proteins in the bilayer?
attached to the outside and sometimes running through the bilayer
Phospholipids are fluid.
- They aren't rigid; they can move. Like cells are in a bubble of oil.
- Proteins are not locked in position.
Fluid Mosaic Structure/Model
Things are embedded in the membrane and can move.
What other things does the fluid nature allow?
- can seal itself
- portions can pinch off (also called vesicles)
- vesicles can fuse with another membrane
protein with a carbohydrate attached
cells to recognize a cell as yours
Integral proteins are amphipathic. Huh?
They have both hydrophobic and hydrophilic parts. That's how they get to stay in the bilayer without moving on through.
Where are integral proteins?
They go from outside to inside, all the way through the bilayer.
What are peripheral proteins?
They just sit on one side of the membrane.
What good is cholesterol?
Helps keep the membrane fluid and helps control what goes in and out
How does membrane structure affect function?
Phospholipid bilayer is selectively permeable.
Why does anyone care that membranes are selectively permeable?
Some stuff can pass through and some can't (from inside or outside)
Polar chemicals can't pass through the membrane.
Cells still need polar stuff, so they use transport proteins to brings stuff.
What about water?
It's small enough to pass through
What types of membrane proteins proteins are there?
- cell surface receptors
- cell surfacce identifiers
- intercellular junctions
- bring stuff into the cell
- must be integral
Cell Surface Receptors
- Chemicals interact with the proteins, but don't pass through them.
- Signal Transduction
Signal transduction (definition)
- the protein takes the message from teh chemical and tells the cell
- a way of detecting things outside the cell
Cell Surface Identifiers
- can be integral or peripheral
- often glycoproteins
- recongize certain cells and how to deal with them
- helps immune system determine what needs to stay/go
some proteins in the membrane act as catalysts to allow reactions to happen
integral proteins attach on one side to the cytoskeleton for stability, on the other side to the extracellular matrix
holds the whole cell in place
- some proteins attach the cell to other cells.
- protein to protein bond of adjacent cells
- (AKA cell adhesion proteins)
How is material transported?
What is diffusion?
net movement of substance from an area of higher concentration to an area of lower concentration
How do things work along a concentration gradient?
- Things still move fairly randomly, but attempts to find equilibrium.
- Substance becomes evenly (randomly) distributed.
Same thing happens with chemicals that can pass through the membrane (SIMPLE DIFFUSION)
Does diffusion along a concentration gradient require energy?
Does not require energy; happens because the stuff wants to be equal.
solute molecule move directly through the membrane due to their own concentration gradient
- Happens when the cell wants a chemical that can't pass through the membrane, but there is still a greater concentration outside, the chemical can move through a transport protein.
- Also doesn't take energy.
diffusion of water through a selectively permeable membrane
As more water moves into a cell...
... osmotic pressure increases to the point of lysis.
How do animal cells respond to isotonic solutions?
no net movement of water
equal solute concentration
higher [solute] outside than inside
How do animal cells respond to hypertonic solutions?
- lower [water] outside than inside
- net loss of water from cell
- cell shrinks, crenation
lower [solute] outside than inside
How do animal cells respond to hypotonic solutions?
- higher [water] outside than inside
- net flow of water into cell
- cell swells
How do plant cells respond to hypotonic solutions?
- Cytoplasm pushes against the cell wall, making the cell inflexible
How do plant cells respond to hypertonic solutions?
- Cell membrane shrinks, pulls away from cell wall
- Plant wilts
Can cells transport substances across the membrane against a concentration gradient?
Yes, but it requires energy.
moving substances across the plasma membrane against the concentration gradient
How does ATP work?
- Has a high energy phosphate bond
- Cell breaks one of these bonds and takes some of its energy
- ATP >> ADP
How does active transport work?
Look it up.
What is an example of active transport?
Sodium-potassium pump info:
- 3 sodium pumped out, 2 potassium pumped in
- allows cell to control volume and maintain osmotic pressure
How are particles transported across the plasma membrane?
Look it up.
Does endocytosis of liquids occur?
How do cells transport material across the plasma membrane?
- simple diffusion
- facilitated diffusion
- active transport
What are the types of endocytosis?
What is phagocytosis?
- folds of plasma membrane surround particle to be ingested, forming small vacuole around it
- vacuole pinches off inside inside cell
- lysosomes fuse with vacuole and pour hydrolytic enzymes onto ingested material
What is pinocytosis?
- tiny droplets of fluid are trapped by folds of plasma membrane
- these pinch off into cytosol as small fluid-filled vesicles
- contents are slowly transferred to the cytosol
How do cells connect together?
What types of cell junctions are there?
Do any cell junctions allow cells to exchange materials?
What are anchoring junctions?
cadherins lock together forming a desmosome
What are cadherins?
fibery things from anchoring junctions
Where are anchoring junctions needed?
What are tight junctions?
totally seal gaps between cells like they are zipped
Where are tight junctions needed?
What are gap junctions?
two cells are joined by connexons that allow passage
What are connexons?
- hollow tubes made of 6 protein strands (ish) that allow cells to exchange materials, electrical charges
- can open or close
Where are gap junctions needed?
What do we mean by energy?
capacity to do work
How do we measure energy?
- kilojoules (kJ)
- 1 kilocalorie = 4.184 kJ
Why isn't energy measured in calories?
Calories really measure heat energy.
What forms of energy exist?
What is potential energy?
- It's called energy because of position or state, not because it's doing anything.
- stored energy
What is kinetic energy?
energy of motion
Any form of energy can...
...be converted into another form.
Potential energy can be converted to...
... kinetic energy. And vice versa.
Chemical energy can be converted to...
... kinetic energy (movement). And vice versa.
Light energy can be converted to...
... chemical energy (photosynthesis).
What is the first law of thermodynamics?
Energy cannot be created or destroyed; it changes from one form to another.
What is the second law of thermodynamics?
Entropy is always increasing.
What is entropy?
Every change in energy...
... loses useful energy as heat.
The universe want energy to...
... be evenly dispersed.
How does this energy stuff influence organisms?
- Organisms must be open systems.
- Organisms must continually obtain energy from their surroundings to do work.
What type of energy is important in chemical reactions?
Gibbs Free Energy (G)
What is free energy?
energy available for work
Where is free energy?
- Most organisms have a certain amount of free energy.
- Most chemical reactions have a change in free energy.
How can a change in free energy occur?
- Exergonic reactions
- Endergonic reactions
- release energy
- are spontaneous
need input of energy
Exergonic reactions are used to...
... provide energy for endergonic reactions.
How is ATP involved in cell energetics?
Cells use ATP to link exergonic and endergonic reactions. (book figure)
How do exergonic and endergonic reactions match metabolism?
- breakdown of large molecules into smaller ones
- Ex. starch -> glucose -> CO2
- makes the energy needed for anabolism
- synthesis of large molecules from smaller ones
- Ex. amino acids -> protein --> muscle (anabolic steroids)
What other types of reactions do cells use to generate energy?
oxidation-reduction reactions (redox)
What do redox reactions involve?
- involves the exchange of electrons
- oxidation = loss of electrons
- reduction = gain of electrons
What is an example of an electron carrier?
- accepts electrons as part of H atoms
How do cells control reactions?
The cell controls the needed energy.
What controls activation energy?
Cells produce enzymes to lower activation energy of specific reactions.
What do catalysts do?
lower the amount of activation energy needed
What are enzymes?
biological catalysts, most are proteins.
- make certain reactions more likely to take place.
- increases rate of reaction.
How do enzymes function?
Adding substrates changes the shape of the enzyme, bring the substrates close enough to react.
What are enzymes like after reactions?
What does the tertiary/quarternary structure of an enzyme do?
gives the enzyme activity
What is the active site of an enzyme?
region where substrates bind
What is an enzyme's allosteric site
any non-catalytic site
How does the cell regulate enzyme activity?
- Only produce enzymes when needed
- Some enzymes need allosteric activation
What do regulator proteins do?
attach to allosteric sites of enzymes, deactivating them
What else affects enzyme activity?
- enzyme and substrate concentration
More enzyme =
More substrate does not =
temporarily stops or slows reactions by blocking active sites
temporarily stops or slows reactions by binding to an allosteric site
inhibitors permanently bind to enzymes, damaging them so they don't work anymore
What is cellular respiration?
cells obtain energy (ATP) from organic compounds
C6H12O6 + O2 --> ENERGY + CO2 + H2O
- This is aerobic respiration because it uses oxygen.
- Actually a series of smaller reactions
What type of process is aerobic respiration?
What are the main processes in cellular respiration?
- 1. glycolysis: glucose --> 2 pyruvate
- acetyl CoA formation: pyruvate --> Acetyl CoA
- 2. citric acid cycle: acetyl CoA --> CO2
- 3. electron transport: transfer electrons to O2
Where does glycolysis take place?
Where cellular respiration (aside from glycolysis) take place?
What is glycolysis?
- occurs in the cytoplasm
- glucose --> 2 pyruvate
What reactions occur during glycolysis?
look it up.
What happens to the pyruvate?
look it up
What happens to the acetyl CoA?
- enters the citric acid cycle
- "acetyl" is converted in CO2
- occurs in mitrondria matrix
What is citric acid cycle AKA?
What does the citric acid cycle produce per acetyl CoA?
What does the citric acid cycle produce per glucose?
What happens to NADH and FADK2?
- Electron (H) carriers
- Pass electrons to ETS
- Inner membrane of mitochondria
What the electron transport system of mitochondria?
inner membrane has proteins that deal with the electrons
How does glycosis occur without oxygen?
- Cells use pyruvate as an electron acceptor in fermentation process
- Not as effective as aerobic, still works
How do cells use lipids for energy?
- Beta Oxidation
- Glycerol -->--> glyceraldehyde-3-phosphate --> glycolysis
How does Beta Oxidation work?
fatty acids -->-->--> Acetyl CoA (which goes to CA cycle)
How do cells use proteins for energy?
look it up