Midterm 2 Flashcards
1
Q
Basic Requirements of a Cell
A
- a system, to encode/transmit information
2.a membrane to separate inside from - ENERGY
2
Q
Energy
A
the capacity to do work or to be transferred as heat
3
Q
Kinetic energy examples
A
- ocean waves, falling rocks, moving hockey puck
- electricity (flow of electrons)
- light (photons)
4
Q
Potential Energy
A
stored energy
5
Q
Potential energy example
A
object, because of its position
- boulder at the top of a hill
6
Q
do electrons further away from the nucleau possess more or less potential energy
A
more
7
Q
what happens when an electron gains energy
A
it moves to a higher energy level that is farther away from the nucleus
8
Q
what forms does energy exist in
A
chemical, electrical, mechanical, electromagnetic radiation, visible light
9
Q
Can energy be transformed between forms
A
yes, flashlight
10
Q
Kinetic energy
A
nergy possessed by an object because it is in motion
11
Q
What is thermodynamics
A
study of energy and its transformations
12
Q
What are the three types of systems
A
open, closed, isolated
13
Q
isolated system
A
does not exchange matter or energy with its surrounding (universe)
14
Q
closed system
A
can exchange energy but not matter with its surroundings (earth)
15
Q
Open system
A
both energy and matter can move freely between the system and surroundings (the ocean absorbs and releases energy/ part if the hydrological cycle)
16
Q
What systems do thermodynamics apply to
A
biotic and abiotic
17
Q
1st law of thermodynamics
A
Energy cannot be created or destroyed, it can only be transferred or transformed.
18
Q
2nd law of thermodynamics
A
The transfer or transformation of energy increases the entropy of a system and its surroundings (entropy is always increasing)
19
Q
What can make reactions spontaneous
A
entropy and enthalpy
20
Q
Entropy (S)
A
The tendency of energy to become dispersed or spread out
21
Q
Can you ever have 100% energy
A
no
22
Q
What happens when energy is transferred or transformed
A
energy is lost
23
Q
When do reactions tend to be spontaneous
A
if products have less potential energy than reactants
24
Q
Total energy = ?
A
Total energy= usable energy+ usable energy
H = G + TS
25
Enthalpy
the heat content of a system ΔH
Reflects the number and kinds of chemical bonds that exist between atoms
26
Exothermic Reactions
Products have less total/thermal energy than reactants
Energy released
-'ve ΔH
spontaneous
27
Endothermic Reactions
Products have more total/thermal energy than reactants
Requires input of energy
+'ve ΔH
Tend to be non-spontaneous
28
Free energy
energy available to do work
29
free energy equation
ΔG = Gproducts - Greactants
ΔG = ΔH − TΔS
30
Two groups of metabolic reactions:
Exergonic, endergonic
31
what do exergonic and endergonic reactions require
activation energy
32
Diffusion
Molecules move spontaneously from higher concentration to lower concentration
33
What is diffusion driven by
increase in entropy and the energy associated with the molecules is spread out
34
equillibrium
maximum stability
35
when is the equilibrium point reached
reactants are converted to products and products are converted back to reactants at equal rates.
36
As a system approaches equilibrium what happens to its free energy
it lowers
37
What kind of system are living systems
open
38
metabolic pathway
series of sequential reactions in which products of one reaction are used immediately as reactants for the next reaction in the series
39
catabolic pathway
Energy is released by breakdown of complex molecules to simpler compounds
40
Anabolic pathway
Consumes energy to build complicated molecules from simpler ones
41
Catabolism vs Anabolism vs metabolism
Catabolism:Breakdown of molecules into smaller units, releasing energy
Anabolism: Building of molecules from smaller units, requiring an input of energy
Metabolism: Collection of all chemical reactions present within a cell or organism
42
ATP Hydrolysis:
ATP hydrolysis releases free energy that can be used as a source of energy for the cell
43
energy coupling
the coupling of an endergonic reaction to an exergonic reaction
44
Enzyme-Catalyzed Reactions
Enzymes bind to a reactant (substrate)
After binding to reactant, and ultimately releasing the product(s), the enzyme is unchanged
Highly specific, recognizing a unique substrate or a class of similar substrates
45
Catalyst
Chemical agent that speeds up the rate of reaction without itself being chemically altered
46
Enzyme Cofactors
Nonprotein groups necessary for catalysis to occur
Cofactors: Metallic ions (Mg2+, Fe2+, Cu2+, Zn2+)
47
Coenzymes
: Organic cofactors such as vitamins
48
Transition state
During catalysis, the substrate and active site of the enzyme form an intermediate transition state
49
Enzymes facilitate the formation of the transition state via 3 major mechanisms:
1. Bringing the reacting molecules into close proximity
2. Exposing the reactant molecules to altered environments that promote their interactions
3. Changing the shape of a substrate molecule
50
When substrate concentration is low:
Reaction rate slows
Enzymes and substrates collide infrequently
51
When substrate concentration is high:
Enzymes become saturated with reactants
Rate of reaction levels off
52
Enzyme inhibitors
nonsubstrate molecules that can bind to an enzyme and decrease its activity
53
Competitive inhibition
Inhibitor competes with the normal substrate for active site
54
Noncompetitive inhibition
Inhibitor does not compete with normal substrate for active site, but combines with sites elsewhere on enzyme
55
Enzyme regulation
Allosteric regulation- occurs with the reversible binding of a regulatory molecule to an allosteric site, a location on the enzyme that is different from the active site
56
Noncompetitive activator
Allosteric activators convert an enzyme from the low to the high affinity state
57
The importance of selectively permeable membranes
Cells and organelles need barrier to separate internal and external contents
58
selectively permeable membrane Barrier must have following qualities:
Impermeable to most molecules and ions
Ability to exchange specific molecules/ions between compartments
Insoluble in water
Permeable to water
59
What is a cellular Membrane
A permeability barrier that consists of:
Phospholipids, glycolipids
Sterols (except in bacteria):
Cholesterol (animals)
Ergosterols (fungi)
Phytosterols (plants)
Membrane proteins
Membrane proteins include:
Integral proteins (transmembrane)
Peripheral membrane proteins
60
Fluid Mosaic Model of Membranes
Membranes are not rigid
They consist of a fluid lipid bilayer in which proteins are embedded and float freely
61
The fluid mosaic model of membrane structure is supported by two major pieces of experimental evidence.
- membranes are fluid
- membrane asemmetry
62
Hydrophobic molecules
No polar regions
Do not interact electrostatically with water
Disrupt hydrogen-bonded structure of water
Tend to coalesce with each other in water
Water molecules tend to exclude molecules that disrupt hydrogen bonding
Hydrophobic interactions are a major driving force in folding of molecules (like proteins), assembly of cellular structures, and membrane organization.
63
Phospholipids are
Amphipathic
64
Amphipathic
Polar head group → Hydrophilic (polar)
2 Non-polar hydrocarbon tails → Hydrophobic (non polar)
65
what is fluidity dependent on
how densely individual lipid molecules can pack together
66
What is maintaining proeper fluidity influenced by
Composition of lipid molecules; Degree of unsaturation of fatty acid tails, Presence of sterols
Temperature
67
phospholipids composed of saturated fatty acids
Each carbon is bound to max number of hydrogens (all single bonds between C’s)
Straight shape
Tighter packing
68
Phospholipids composed of unsaturated fatty acids
Double-bonds between carbons
introduce kinks
Less dense packing
69
what happens at low temperatures
At low temperatures → enzymes and proteins cannot function if fluidity is not maintained
70
what happens at high temperatures
At high temperatures → Too fluid, get leakage
71
what do organisms do to optimize fluidity
Organisms can modify the lipid composition of their membranes to optimize fluidity in response to different temperatures by changing:
72
key functions of membrane proteins
1. transport
2. enzymatic activity
3.signal transduction
4. attachment/recognition
73
Integral Membrane Proteins
Proteins embedded in phospholipid bilayer
74
what are integral memebrane proteins composed of
predominantly nonpolar amino acids usually coiled into alpha helices
75
Peripheral Membrane Proteins
On surface of membrane
Do not interact with hydrophobic core
Held together by noncovalent bonds
Many on cytoplasmic side of membrane
Made up of mixture of polar and non- polar amino acids
76
Integral Membrane Proteins Interact with ...
the Membrane Hydrophobic Core
77
Peripheral Membrane Proteins Interact with...
the Membrane Hydrophilic Surface
78
Passive Membrane Transport
Movement of molecules across a membrane without need to expend chemical energy such as ATP
79
what is passive transport driven by
diffusion
80
Diffusion
Net movement of substance from region of higher to lower concentration
81
driving force of diffusion
increase in entropy
82
There Are Two Types of Passive Transport
simple, facilotated
83
Simple diffusion
Passive transport of molecules across a membrane without the involvement of a transporter
84
Facilitated Diffusion
Passive transport of molecules across a membrane with the aid of a transporter
85
Carrier Proteins
Bind a specific single solute and transport it across the lipid bilayer (uniport transport)
Undergo conformational changes that move the solute-binding site from one side of the membrane to the other
Can become saturated when there are too few transport proteins to handle all the solute molecules
86
Most proteins that carry out facilitated diffusion of ions are controlled by
“gates” that open or close their transport channels
87
Gates can be opened or closed in response to various stimuli, such as
voltage across the membrane or the presence of signal molecules
88
Osmosis
Diffusion of water molecules
89
Water can move (slowly) across membranes by
simple diffusion
90
water moves from
From hypotonic solution (lower concentrations of solute molecules) To hypertonic solution (higher concentrations of solute molecules)
91
Active transport requires
a direct or indirect input of energy derived from ATP hydrolysis or concentration gradients
92
Active Membrane Transport Moves substances against
against their concentration gradients; requires cells to expend energy
93
Active Membrane Transport depends on
membrane transport proteins
94
Two Kinds of Active Transport:
primary and secondary
95
Primary active transport
Same protein that transports the molecules also hydrolyzes ATP to power transport directly
96
Secondary active transport
Transport indirectly driven by ATP hydrolysis
97
Primary Active Transport
Moves positively charged ions across membranes
- H+ pumps (proton pumps)
Cells lining stomach
- Ca2+ pump
Maintain low intracellular Ca2+ concentration
Na+/K+ pump
-- 3 Na+ out, 2 K+ in for every pump cycle
Creates negative membrane potential
Electrochemical gradient across membrane
98
Secondary Active Transport involves
symport and antiport
99
symport
Cotransported solute moves through
membrane channel in same direction
as driving ion
100
antiport
Driving ion moves through membrane
channel in one direction, providing
energy for active transport of another
molecule in opposite direction
101
Exocytosis and endocytosis move
large molecules and particles in and out of cells
102
Exocytosis
Secretory vesicle carries secreted materials
Moves through cytoplasm and contacts the plasma membrane
Vesicle membrane fuses with plasma membrane, releasing contents to cell exterior
103
Endocytosis
Encloses materials outside cell in plasma membrane
Pockets inward and forms endocytic vesicle onmcytoplasmic side
104
Two forms of endocytosis
Bulk-phase (pinocytosis)
Receptor-mediated endocytosis
105
Receptor-Mediated Endocytosis
Molecules bind to receptor proteins on outer cell surface
After binding, receptors collect into a depression in PM called a coated pit
- Network of proteins, called clathrin, on cytoplasmic side
Pit pinches off PM to form endocytic vesicle
106
Why is membrane signaling important?
Ability to sense and respond to external stimuli, or changes in the environment, is a key characteristic of life
107
steps in cell signalling
receptor activation, signal transduction, response, termination
108
Reception by a Cell-Surface Receptor
Signal molecules: Hormones, Neurotransmitters
Receptors:Integral membrane glycoproteins
Responses usually rapid,short-lived events (regulate enzyme activity)
109
Reception by a Receptor Within Cell
Signal molecules: Steroid hormones -testosterone, estrogen
Intracellular receptors: Steroid hormone receptor- Hormone-binding domain & DNA-binding domain
Responses typically occur over a longer time due to changes in gene expression
110
Cell communication systems based on surface receptors have three components:
Extracellular signal molecules
Surface receptors that receive the signals
Internal response pathways triggered when receptors bind a signal
