Exam 2 Flashcards
Define selective permeability
Allowing some substances to cross it more easily than others
What is the fluid mosaic model?
Used to demonstrate the membrane is a “mosaic” of various proteins dispersed within the bilayer, with only the hydrophilic regions exposed to water
True or False: Phospholipids within the plasma membrane can move within the bilayer
True
True or False: Proteins can not move within the bilayer
False
As temperatures cool, membranes switch from a fluid state to a …
Solid state
True or false: The fluidity of a plasma membrane is affected by the type of hydrocarbon tails in phospholipids
True
At lower temperatures, the Plasma Membrane is more fluid if…
Unsaturated hydrocarbon tails with kinks are present
The plasma membrane is less fluid if…
Saturated hydrocarbon tails are present
Define viscous
Less warm temperatures, cholesterol makes the membrane less fluid by restraining the movement of phospholipids
How does chloesterol effect membrane fluidity at warm temperatures?
cholesterol makes the membrane less fluid by restraining the movement of phospholipids
How does cholesterol effect membrane fluidity at low temperatures?
At low temperatures, it maintains fluidity by preventing tight packing
What are integral proteins?
- Penetrate hydrophobic core
- Often transmembrane proteins
- Located all over the membrane
What are peripheral proteins?
- not embedded in lipid bilayer
- appendages are loosely bound to the surface of the membrane
What are the six major functions of membrane proteins?
- transport
- enzymatic
- attachment to cytoskeleton and extracellular matrix
- cell-cell recognition
- intercellular joining
- signal transduction
What is cell-cell recognition?
The cell’s ability to distinguish one type of neighboring cell from another
What is the purpose of membrane carbohydrates?
To interact with surface molecules of other cells, facilitating cell-cell recognition
How are glycolipids formed?
Membrane carbs covalently bonded to lipids
How are glycoproteins formed?
Membrane carbs covalently bonded to proteins
Molecules that start on the inside face of the ER…
End up on the outside face of the plasma membrane
When is symmetrical distribution of proteins, lipids, and assorted carbs in the plasma membrane determined?
When the membrane is built by the ER and the Golgi apparatus
What causes selective permeability?
Membrane structure
What is selective permeability?
When a cell must exchange materials with its surroundings, a process controlled by the plasma membrane
Describe the permeability of hydrophobic molecules?
- Nonpolar
- Hydrocarbons, CO2, O2
- Pass through membrane easily
Describe the permeability of hydrophilic molecules?
- Polar
- Sugars, H20, C6H12O6
- Do not pass through the membrane easily
Describe the permeability of ions?
- Na+, K+
- A charged atom and its surrounding shell of water
- Require transport proteins
What are the three mechanisms of transport?
Active
Passive
Bulk
What is passive transport?
- Substances diffuse DOWN the gradient
- Does not require ATP
- Facilitated diffusion included
What is active transport?
- Substances move against gradient
- ATP required
- Includes ion pumps and cotransports
What is bulk transport?
-Includes exocytosis and endocytosis
Define Osmosis
Mechanism of passive transport
Diffusion of water across a semipermeable membrane
How is the direction of osmosis determined?
By a difference in total solute concentration
True or false: Water diffuses from region of higher to lower solute concentration
FALSE
Define tonicity
Ability of a solution to cause a cell to gain/lose water
True or False: cells without rigid cell walls have osmotic problems in either a hypertonic or hypotonic environment
True
How do cells without rigid cell walls maintain internal environment?
Osmoregulation
Define osmoregulation
Control of water balance
What is special about the protist Paramecium?
It is hypertonic to its pond environment and has a contractile vacuole that acts as a pump
Define hypotonic
- When solute concentration is less outside than inside the cell (cell gains water)
- A cell swells until cell wall opposes uptake
What is the term for a hypotonic plant cell?
Turgid
Define hypertonic
- When solute concentration is greater outside than inside the cell (cell loses water)
- Membrane pulls away from cell wall (defined as plasmolysis)
What is the term for a hypertonic plant cell?
Plasmolyzed
Define isotonic
When solute concentration is the same inside as outside the cell (no net water movement)
What is the term for an isotonic plant cell?
Flaccid
What is the optimal environment for an animal cell?
Isotonic
What is the optimal environment for a plant cell?
Turgid (hypotonic)
True or False: Cell walls do not help maintain water balance
FALSE
Define transport proteins
Allow passage of hydrophilic substances across a membrane and are specific for the substance they move
What are channel proteins?
Have a hydrophilic channel that certain molecules or ions can use as a tunnel
Define aquaporins
Facilitate passage of water
Define carrier proteins
Bind to molecules to change shape to shuttle them across the membrane
Why is facilitated diffusion passive?
The solute moves down its concentration gradient
What are the inputs and outputs of the sodium potassium pump?
3 Na+ out
2 K+in
1 ATP used
What kind of transport mechanism is the Sodium Potassium pump?
Active
What is membrane potential?
Voltage difference across a membrane
True or false: the inside of the cell is negative compared to the outside
TRUE
Membrane potential favor the passive transport of ____ into the cell and _____ out of the cell
cations, anions
What is the electrochemical gradient?
2 combined forces driving the diffusion of ions across a membrane
What are the two forces of the electrochemical gradient?
Chemical and Electrical
What is the chemical component of the electrochemical gradient?
The ion’s concentration gradient
What is the electrical component of the electrochemical gradient?
Effect of the membrane potential on the ion’s movement
What is the electrogenic pump?
A transport protein that generates the voltage across a membrane
What are the typical examples of the electrogenic pump?
Sodium potassium pump (In animals) Proton pump (plants, fungi, bacteria)
Define cotransport
Occurs when active transport of a solute indirectly drives transport of another solute
What is the proton pump
Plants generally use gradient of H+ ions generated by proton pumps to drive active transport of nutrients into the cell
What is bulk transport?
- Small molecules and water enter or leave the cell through the lipid bilayer or by transport proteins
- Large molecules such as polysaccharides and proteins cross the membrane via vesicles
Define exocytosis
- transport vesicles migrate to membrane, fuse with it, and release their contents
- addition of plasma membranes
True or False: Many secretory cells use exocytosis to export their products
TRUE
Define endocytosis
- The cell takes in molecules by forming vesicles from the plasma membrane
- loss of plasma membrane
True or False: Endocytosis is a reversal of exocytosis involving different proteins
TRUE
What are the three types of endocytosis?
Phagocytosis
Pinocytosis
Recepter Mediated
What is Phagocytosis?
“Cellular eating”
Cell engulfs a particle in a vacuole
What is Pinocytosis?
“Cellular drinking”
cell creates vessicle around fluid
What is receptor mediated endocytosis?
Binding of ligands to receptors triggers vesicle formation
How does phagocytosis occur?
A cell engulfs a particle by wrapping pseudopodia around it, and packaging it within a vacuole. The particle is digested after the vacuole fuses with a lysosome containing hydrolytic enzymes
How does pinocytosis occur?
- The cell gulps tiny droplets of extracellular fluid to tiny vesicles.
- It is not the fluid itself that is needed by the cell, but the mlcs dissolved in the droplets.
- Nonspecific in the protein substances it transports
Define Ligand
Any molecule that binds specifically to a receptor site of another molecule
How does receptor mediated endocytosis occur?
Enables the cell to acquire bulk quantities of specific substances, even though these substances may not be very concentrated in the extracellular fluid
Describe intracellular receptors
- Flourid in the cytosol/nucleus of target cells
- small hydrophobic chemical messengers can easily cross membrane and activate receptors
What are examples of intracellular receptors?
Steroid and thyroid hormones of animals.
What is the role of an activated hormone receptor?
It can act as a transcription factor, turning on specific genes
Describe Protein Phosphorylation and Dephosphorylation
- Signal is transmitted by a CASCADE of protein phosphorylations
- This phosphorylation and dephosphorylation system act as a molecular switch
What is the role of the protein kinase?
Transfer phosphate groups from ATP to a protein
What is the role of the protein Phosphatase
To remove the phosphates
Describe the response of the phosphorylation and dephosphorylation
- other pathways regulate the activity of enzymes
- At each step, the number of activated products is much greater in the preceding step
- ultimately a signal transduction pathway leads to regulation of one or more cellular activities
Define metabolism
- The totality of an orgnaism’s chemical reactions
- an emergent property of life that arises from interactions between molecules within the cell
A metabolic pathway
- Begins with a specific molecule and ends with a product
- Each step is catalyzed by a specific enzyme
What is an exergonic reaction?
- releases energy that can perform work
- spontaneous
- negative delta G
- catabolism
- Goes down on a graph
What is an endergonic reaction?
- Requires energy to perform work
- nonspontaneous
- positive delta G
- anabolism
- Goes up on a graph
What are the three types of work performed by the cell?
Chemical
Mechanical
Transport
How do cells perform work?
They manage energy resources by energy coupling
Define energy coupling
Use of an exergonic process to drive an endergonic one
How are the bonds between phosphate groups of ATP’s tail broken?
Hydrolysis
True or False: Energy is released from ATP when the terminal phosphate bond is broken
TRUE
Why does this release of energy occur?
The chemical change to a state of lower free energy, NOT the phosphate bonds
True or false: The energy from the exergonic reaction of ATP hydrolysis can not be used to drive an endergonic reaction
FALSE
True or False: ATP drives chemical work
TRUE
Chemical work consists of:
- coupled reactions
- overall delta g is negative
- together the reactions are spontaneous
During Transport work
ATP phosphorylates transport proteins
During Mechanical work
ATP binds noncovalently to motor proteins and then is hydrolyzed
How is ATP a renewable resource?
It is regenerated by addition of a phosphate group to ADP
Where does the energy used to phosphorylate ADP come from?
Catabolic reactions in the cell
Where is chemical potential energy stored?
ATP and drives most cellular work.
Define catalyst
A chemical agent that speeds up a reaction without being consumed by the reaction
What is an example of a catalytic protein?
An enzyme
What is an example of an enzyme catalyzed reaction?
Hydrolysis of sucrose by the enzyme sucrase
What is activation energy (Ea)-
-Initial energy needed to start a chemical reaction
How is activation energy supplied?
The form of heat from surroundings
How do enzymes lower the Ea barrier?
-Enzymes catalyze reactions
What are the effects of enzymes on free energy and the rate of reactions?
Enzymes do not effect Ea and hasten reactions that would occur eventually
How are enzyme-substrate complexes formed?
When enzymes bind to the substrate
What is the active site?
Region on the enzyme where the substrate binds
What is the induced fit of a substance
Brings chemical group of the active site into positioins that enhance their ability to catalyze the chemical reaction
What can effect an enzyme’s activity?
- Temperature
- pH
- Chemicals that specifically influence the enzyme
True or false: Each enzyme does not require an optimal temperature and pH in which it can function
FALSE
Define cofactors
- Non protein enzyme helpers
- Inorganic
- Tightly bound
What are some examples of cofactors?
Iron, zinc, copper
What are coenzymes
- Organic cofactors
- Loosely bound
- Released as normal part of the catalytic cycle
What are the two types of enzyme inhibitors
Irreversible and reversible inhibitors
What are irreversible inhibitors?
Inhibitor usually attaches to the enzyme by covalent bonds
What are examples of irreversible inhibitors?
Some toxins and poisons, penicllins
What are the two types of reversible inhibitors?
Competitive and noncompetitive
What are competitive inhibitors?
- They bind to the active site of an enzyme, competing with the substrate
- can be overcome by increasing the concentration of the substrate
What are noncompetitive inhibitors?
-They bind to another part of an enzyme causing it to change shape and making active sites less effective.
True or False: Regulation of enzyme activity helps control metabolism
TRUE
What would result if a cell’s metabolic pathways were not tightly regulated?
Chemical chaos
What is allosteric regulation?
- When a protein’s function at one site is affected by binding of a regulatory molecule at another site
- May either inhibit or stimulate an enzyme’s activity
What are most allosterically regulated enzymes made from?
Polypeptide subunits
How does binding of an activator enzyme effect the form of the enzyme?
It stabalizes the active form of the enzyme
How does the binding of an inhibitor enzyme effect the form of the enzyme?
It stabalizes the inactive form of the enzyme
What are the activators and inhibitors of the catabolic enzymes when they regenerate ATP?
Activator: ADP
Inhibitor: ATP
Define cooperativity
A form of allosteric regulation that can amplify enzyme activity
How does cooperativity work?
Binding of one substrate molecule to active site of one subunit locks all subunits in active conformation
Define feedback inhibition
The end product of a metabolic pathway shuts down the pathway
How does feedback inhibition work?
It prevents a cell from wasting chemical resources by synthesizing more product than is needed
What do catabolic pathways do?
Breakdown organic molecules
Define cellular respiration
Breakdown of organic molecules for production of ATP
What is aerobic respiration?
Respiration that consumes oxygen
What is the chemical formula of cellular respiration?
C6H12O6 + 6O2 ——> 6CO2 + 6H20 + ATP
What is anaerobic respiration?
Use inorganic molecules other than the oxygen as the final electron acceptor at the end of the electron transport chain
Define fermentation
A partial degradation of sugars that occurs without oxygen
What is an oxidation-reduction reaction?
Chemical reactions that transfer electrons by reactants
How do you determine what reactant is oxidized/reduced
LEO goes GER
- Loses electrons=oxidized
- Gains electrons=reduced
How do you determine what reactant is the oxidzing/reducing agent?
Electron donor=reducing agent
electron acceptor=oxidizing agent
How do you label the reactants in a redox reaction when charges aren’t present?
- Oxidized gain O, lose H
- Reduced gain H, lose O
During cellular respiration, what is oxidized and what is reduced?
Glucose is oxidized
Oxygen is reduced
What are the stages of cellular respiration?
Glycolysis
Pyruvate oxidation (acetyl coA formation)
Citric acid cycle
Oxidative phosphorylation
Define glycolysis
- Breaks down glucose into two molecules of pyruvate
- Does not require oxygen
- Occurs in cytoplasm
What are the two phases of glycolysis
Energy investment
energy pay off
What are the net inputs and net outputs of glycolysis?
Inputs: Glucose, 2 NAD+, 4 ADP +P
Outputs: 2 pyruvates, 2 ATP, 2 NADH, 2 H2O
Define pyruvate oxidation (acetyl coA formation)
Completes breakdown of glucose
What are the net outputs of pyruvate oxidation?
2CO2, 2 NADH, 2 Acetyl CoA
Define citric acid cycle
Completes breakdown of glucose
Has 8 steps each catalyzed by a specific enzyme
What are the net inputs and net outputs per glucose of the Citric acid cycle?
Inputs: 2 FAD, 6 NAD+, 2ADP
Outputs: 4CO2, 2 FADH2, 6 NADH, 2 ATP
How do the inputs out and outputs differ if it were asked per pyruvate?
It is just half of each
Following glycolysis and the citric acid cycle, what accounts for most of the energy extracted from food?
NADH and FADH2
What electron carriers donate electrons to the ETC?
NADH and FADH2
What does donation to the ETC do?
Powers ATP synthesis via oxidative phosphorylation
What are most of the ETC’s components?
Proteins
What is the final proton acceptor?
O2
Define Oxidative Phosphorylation
Accounts for most of the ATP synthesis, powered by redox reactions
Where is the ETC located?
The cristae of the mitochondrion (inner membrane)
Where does kreb’s cycle occur?
Matrix
Does the ETC gnereate ATP directly?
No. It releases energy in manageable amounts
What is an example of chemiosmosis?
The use of energy in a H+ gradient to drive cellular work
Describe the process of chemiosmosis
- Electron transfer in ETC causes proteins to pump H+ from the mitochondrial matrix to the intermembrane space
- H+ then moves back across the membrane, passing through channels in ATP synthase that uses the exergonic flow of H+ to drive phosphorylation of ATP
What are the two components of oxidative phosphorylation?
- ETC
- Chemiosmosis
Describe the energy flow during cellular respiration
Glucose —-> Electron Carriers —-> ETC —-> Proton-motive force —-> ATP
How many ATP are made during cellular respiration?
30-32 ATP
How many ATP are made during glycolysis?
2 ATP
How many ATP are made during citric acid cycle?
2 ATP
How many ATP are made during Oxidative Phosphorylation?
26-28 ATP
What kind of phosphorylation are glycolysis and citric acid cycle?
Substrate level phosphorylation
Can glycolysis produce ATP with/without oxygen?
Yes
In the absence of O2, how does glycolysis produce ATP?
Anaerobic respiration, uses an ETC with a different final proton acceptor
Define fermentation
Glycolysis plus reactions that regenerate NAD+ which can be reused by glycolysis
What are the two types of fermentation?
alcohol and lactic acid
Describe alcohol fermentation
- Pyruvate is converted to ethanol in two steps, the first releases CO2
- ex// yeast used in brewing
Describe Lactic acid fermentation
- pyruvate reduced to NADH forming lactate as an end product
- ex// some fungi and bacteria, muscle cells
How do muscle cells used lactic acid
To generate ATP when O2 is scarce
To sustain high rates of glycolysis under anaerovic conditions, cells require
NAD+
Describe facultative anaerobes
- can survive using fermentation or cellular respiration
- ex// yeast, bacteria
Describe obligate anaerobes
-carry out fermentation or anaerobic respiration and cannot survive in presence of O2
What is the evolutionary significance of glycolysis
Glycolysis evolved in ancient prokaryotes before there was oxygen in the atmosphere
Describe Catabolism
- funnel electrons from many kinds of organic molecules into cellular respiration
- proteins are digested to amino acids
- fats digested to glycerol and fatty acids
How do amino groups contribute to glycolysis or the citric acid cycle
they feed the two processes
How is glycerol used?
Used in glycolysis
How are fatty acids used?
Used to generate acetyl coA
When fatty acids are broken down by beta oxidation what do they yield?
Acetyl CoA
Describe biosynthesis (Anabolic pathways)
Body uses small molecules to build other substances
What is the most common mechanism for control of cellular respiration?
Feedback Inhibition
If ATP concentration begins to ____ respiration ____; When there is _____ respiration _____
- drop, speeds up
- plenty of ATP, slows down
What is the equation for photosynthesis?
6 CO2 + 6 H20 —> C6H12O6 + 6 O2
Where do light reactions occur?
The thylakoids
What does the process of light reactions do?
- split water
- release O2
- Produce ATP (by phosphorylation)
- Form NADPH
Where does the Calvin cycle take place?
The stroma
What does the calvin cycle do?
Form sugar from CO2 using ATP and NADPH
What is Chlorophylla
-main photosynthetic pigment
What does Chlorophyll b do?
Broadens spectrum used for photosynthesis
What are carotenoids?
accessory pigments that absorb excessive light that would damage chlorophyll
A photosystem consists of…
reaction center surrounded by light harvesting complexes
What are light harvesting complexes?
pigment molecules bound to proteins
What do light harvesting complexes do?
funnel the energy of photons to the reaction center
What accepts an excited electron from chlorophyll a
primary electron acceptor in the reaction center
What is the first step of the light reactions?
solar powered transfer of an electron from chloryphyll a molecule to primary electron acceptor
What order are the photosystems in?
II first I second
What wavelength does PS II absorb?
p680
What wavelength does PS I absorb?
p700
What do the two photosystems generate?
ATP and NADPH
What are the two routes for electron flow during the light reaction?
Linear (noncyclic) or Cyclic
What is Linear (noncyclic) pathway
primary pathway
involves both photosystems
produces ATP and NADH
What is cyclic pathway
uses only PS I
Produces only ATP
Generates surplus ATP satisfying higher demand in calvin cycle
How do chloroplasts and mitochondria generate atp and what sources of energy do they use?
Chemiosmosis
mitochondria: transfer chemical energy from food to ATP
chloroplasts: transform light energy into chemical energy of ATP
True or false: Clavin cycle are reffered to as light independent reactions
TRUE
What are light independent reactions
Don’t require light directly, and occur in daylight
During Calvin cycle carbon enters the cycle as CO2 and leaves as a sugar named
Glyceraldehyde 3 Phosphate (G3P)
How many times must Calvin cycle take place to generate one G3P? How many CO2 are produced?
Three times, 3 CO2
What are the three phases of Calvin Cycle?
Carbon fixation
Reduction
Regeneration of the CO2 acceptor
WHat is carbon fixation catalyzed by?
Rubisco
What is the CO2 acceptor?
RuBP
To generate one G3P mlc, you need
9 ATP
6 NADPH
What are alternative mechanisms of carbon fixation?
dehydration
On hot dry days plants close to ____ which conserves water but also limits photosynthesis
stromata
During photorespiration
- Rubisco adds O2 to the calvin cycle instead of CO2
- Neither ATP or sugar are produced
- may be an evolutionary relic because rubisco first evolved when atmosphere had more CO2 than O2
Describe C4 Plants
- Minimize cost of photorespiration by incorporating CO2 into 4 carbon compounds
- These compounds are exported to bundle-sheath cells where they release CO2 that is then used in Calvin cycle
Describe CAM plants
- Open stromata at night to incorporate CO2 into organic acids
- Stomata close during day and CO2 released from organic acids and used in calvin cycle.
