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Biology 100 > Biology 203 (Exam 2) > Flashcards

Biology 203 (Exam 2) Flashcards

(80 cards)

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1
Q

Free-Energy Change △G

Biologists:

A 
－Want to know which reactions occur
spontaneously and which require input
of energy
– To do so, Biologists need to
determine energy changes that occur
in chemical reactions
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2
Q

Free-Energy Change △G

The free-energy change of a reaction

A

Tells us whether or not the reaction

occurs spontaneously

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3
Q

A living system’s free energy

A 
Energy that can do work when
temperature and pressure are
uniform
• As in a living cell
• △G must have a negative value
for a process to be spontaneous

△G = Gfinal state – Ginitial state

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4
Q

Free energy is a measure of a system’s instability

A

Its tendency to change to a more stable state

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5
Q

During a spontaneous change

A

－Free energy decreases and the stability of a system
increases
– Unless something prevents it, each system will move
toward greater stability
• Diver on a top of a platform
• Drop of concentrated dye
• Sugar molecule

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6
Q

Equilibrium is a state of maximum stability

A

A process is spontaneous and can perform work only when it is moving toward equilibrium.

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7
Q

The change in free energy (△G) during a process

A

Related to the change in enthalpy or change in total energy (△H), change in entropy (△S), and temperature in Kelvin (T)

△G = △H - T△S

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8
Q

Free energy extra

A

Only processes with a negative ΔG are spontaneous
• Spontaneous processes can be harnessed to perform
work

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9
Q

Equilibrium and Metabolism

The concept of free energy :

A

Can be applied to the chemistry of life’s processes

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10
Q

Exergonic and endergonic reactions in metabolism

A

An exergonic reaction
■Proceeds with a net release of free energy and is spontaneous

An endergonic reaction
▪ Absorbs free energy
from its surroundings
and is nonspontaneous

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11
Q

Reactions in a closed system

A

Eventually reach equilibrium and then do no work

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12
Q

Cells are not in equilibrium

A

They are open systems experiencing a constant flow of material

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13
Q

A catabolic pathway in a cell

A

Releases free energy in a series of reactions

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14
Q

Closed and open hydroelectric systems

A

Can serve as analogies.

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15
Q

A defining feature of life

A

Metabolism is never at equilibrium

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16
Q

ATP

A

powers cellular work by coupling exergonic reactions to endergonic reactions

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17
Q

A cell does three main kinds of work:

A

– Chemical
• Coupling energy from ATP (△G 0)

– Transport
• Pumping ions and molecules across
membranes against concentration
gradient

– Mechanical
• muscle contraction, vesicle,
flagella and cilia movement

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18
Q

To do work, cells manage energy resources by energy coupling

A

The use of an exergonic process to drive an endergonic one

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19
Q

Most energy coupling in cells is mediated by ATP

A

－Cell’s energy shuttle

– Composed of ribose (a sugar), adenine
(a nitrogenous base), and three
phosphate groups

– The bonds between the phosphate
groups of ATP’s tail can be broken by
hydrolysis

– Energy is released from ATP when the
terminal phosphate bond is broken

– This release of energy comes from the
chemical change to a state of lower
free energy
        • Not from the phosphate bonds
           themselves
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20
Q

How ATP performs work

A

The three types of cellular work are powered by the hydrolysis of ATP
－Mechanical
– Transport
– Chemical

In the cell
– Energy from the exergonic
reaction of ATP hydrolysis
• Can be used to drive an endergonic reaction

Overall, the coupled reactions
are exergonic

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21
Q

ATP drives endergonic

reactions by phosphorylation

A

Transferring a phosphate group to some other molecule
• Such as a reactant

The recipient molecule becomes phosphorylated

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22
Q

ATP is a renewable resource

A

Regenerated by addition of a phosphate group to adenosine diphosphate (ADP)

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23
Q

The energy to phosphorylate ADP

A

Comes from catabolic reactions in the cell

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24
Q

The chemical potential energy

A

Temporarily stored in ATP drives most cellular work

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25
A catalyst
A chemical agent that speeds up a reaction | • Without being consumed by the reaction
26
An enzyme
– A catalytic protein
27
Hydrolysis of sucrose by the | enzyme sucrase
An example of an enzymecatalyzed | reaction
28
Every chemical reaction | between molecules
Involves bond breaking and | bond forming
29
The initial energy needed to | start a chemical reaction
Activation energy (EA)
30
Activation energy
Often supplied in the form of heat from the | surroundings
31
Enzymes catalyze reactions
by | lowering the EA barrier
32
Enzymes do not affect the change | in free energy (ΔG)
Instead, they hasten reactions that would occur | eventually
33
The reactant that an enzyme acts on
– Called the enzyme’s substrate
34
The enzyme binds to its substrate
Forming an enzyme-substrate complex
35
The active site
The region on the enzyme where the substrate binds
36
Induced fit of a substrate
－Brings chemical groups of the active site into positions | – Enhance their ability to catalyze the reaction
37
In an enzymatic reaction
Substrate binds to the active | site of the enzyme
38
The active site can lower an EA barrier by
``` －Orienting substrates correctly – Straining substrate bonds – Providing a favorable microenvironment – Covalently bonding to the substrate ```
39
An enzyme’s activity can be | affected by
－General environmental factors, such as temperature and pH – Chemicals that specifically influence the enzyme
40
Effects of Temperature and pH
``` －Each enzyme has an optimal temperature in which it can function – Each enzyme has an optimal pH in which it can function ```
41
Cofactors
``` Cofactors are nonprotein enzyme helpers – May be inorganic • metal in ionic form – May be organic • coenzyme ``` ``` Coenzymes include vitamins • Vitamin C – Ascorbic acid – Scurvy – Required for the synthesis of collagen – Bleeding from mucous membranes, spots on skin ```
42
Enzyme Inhibitors
Competitive inhibitors – Bind to the active site of an enzyme – Competing with the substrate Noncompetitive inhibitors – Bind to another part of an enzyme – Causing the enzyme to change shape – Making the active site less effective
43
Regulation of enzyme activity
Helps control metabolism
44
Living cells require energy | from outside sources
``` －Some animals, such as the giant panda, obtain energy by eating plants – Some animals feed on other organisms that eat plants ```
45
Energy flows into an ecosystem as sunlight
Leaves as heat
46
Photosynthesis generates O2 and organic molecules
Used in cellular respiration
47
Cells use chemical energy stored in organic molecules
－Regenerate ATP | • Powers work
48
Stages of Cellular Repsiration | A Preview
Cellular respiration has three stages: - Glycolysis * Breaks down glucose into two molecules of pyruvate - The citric acid cycle * Completesthe breakdown of glucose - Oxidative Phosphorylation * Accounts for most of the ATP synthesis
49
Cellular Respiration
Includes both aerobic and anaerobic respiration ``` – Often used to refer to aerobic respiration • Although carbohydrates, fats, and proteins are all consumed as fuel ``` ``` – Helpful to trace cellular respiration with the sugar glucose: Cellular Respiration C6H12O6 + 6 O2 >>>> 6 CO2 + 6 H2O + Energy (ATP + heat) ```
50
Redox Reactions: Oxidation and Reduction
* The transfer of electrons during chemical reactions – Releases energy stored in organic molecules • This released energy is ultimately used to synthesize ATP
51
The Principle of Redox (slide 6, ch10)
``` --Chemical reactions that transfer electrons between reactants are called oxidation-reduction reactions • Redox reactions – In oxidation • A substance loses electrons – Oxidized – In reduction • A substance gains electrons – Reduced – The amount of positive charge is reduced ```
52
Reducing Agents and Oxidizing Agents
*The electron donor – Called the reducing agent • The electron acceptor – Called the oxidizing agent • Some redox reactions do not transfer electrons – But change the electron sharing in covalent bonds – An example is the reaction between methane and O2
53
During cellular respiration
``` The fuel (such as glucose) is oxidized –O2 is reduced ```
54
Electron transport chain
``` Passes electrons in a series of steps • Breaks the fall of e- – Unlike an uncontrolled, explosive reaction ``` *O2 pulls electrons down the chain in an energy-yielding tumble • The energy yielded is used to regenerate ATP
55
Nicotinamide adenine | dinucleotide (NADH)
passes the electrons to the electron transport chain
56
Niacin
Vitamin B3
57
Pellagra
Vitamin deficiency disease
58
Tradition food preparation of corn
``` Treatment with lime • An alkali • Makes niacin nutritionally available • Corn dependence in Spain, American South (1900s) • No lime treatment • Pellagra first described • Aggression • Skin lesions • Dilated cardiomyopathy • Dementia • Death in 5 years ```
59
In cellular respiration:
Glucose and other organic molecules are broken down in a series of steps
60
Electrons from organic compounds are usually first transferred to NAD+
– A coenzyme
61
NAD+ functions as an oxidizing agent during cellular respiration
NAD+ is an electron acceptor
62
Each NADH (the reduced form of NAD+)
Represents stored energy | – Tapped to synthesize ATP
63
Glycolysis
``` “Splitting of sugar” – Breaks down glucose into two molecules of pyruvate – Occurs in the cytoplasm – Two major phases • Energy investment phase • Energy payoff phase ```
64
Energy Investment | Phase
``` Glucose enters the cell • Phosphorylated by hexokinase – Sugar trapped in cell – More chemically reactive – Transfer of a phosphate group • Investment of energy ```
65
Glycolisis: Energy Investment | Phase
``` Glucose-6-phosphate converted to its isomer • Fructose-6- phosphate ```
66
aerobic respiration takes place in about 20 steps, grouped into three stages:
1) Glycolysis 2) Formation of acetyl coenzyme A and the citric acid cycle (Krebs cycle) 3) The electron transport chain and chemiosmosis
67
Cellular respiration has three stages:
``` – Glycolysis • Breaks down glucose into two molecules of pyruvate – The citric acid cycle • Completes the breakdown of glucose – Oxidative phosphorylation • Accounts for most of the ATP synthesis ```
68
Oxidative Phosphorylation
• Process that generates most of the ATP – Powered by redox reactions • Oxidative phosphorylation – Accounts for almost 90% of the ATP generated by cellular respiration • A smaller amount of ATP is formed in glycolysis and the citric acid cycle – Substrate-level phosphorylation
69
During Oxidative Phosphorylation
Chemiosmosis Couples Electron Transport To ATP Synthesis Following glycolysis and the citric acid cycle, • NADH and FADH 2 account for most of the energy extracted from food • These two electron carriers donate electrons to the electron transport chain • Powers ATP synthesis via oxidative phosphorylation
70
Chemiosmosis
Diffusion of ions across a selectively-permeable membrane | • Generation of ATP by the movement of hydrogen ions across a membrane during cellular respiration
71
The Pathway of Electron Transport
``` Electron transport chain – In the cristae of the mitochondrion • Most of the chain’s components are proteins – Exist in multiprotein complexes – Flavoprotein (FMN) – Iron-sulfur protein (Fe-S) – Ubiquinones (Q) – Cytochromes (Cyt) • The carriers alternate reduced and oxidized states – As they accept and donate electrons • Electrons drop in free energy as they go down the chain – Finally passed to O2 • Forming H2O ```
72
Chemiosmosis Couples The Electron Transport | Chain to ATP Synthesis
Energy stored in a H+ gradient across a membrane – Couples the redox reactions of the electron transport chain to ATP synthesis • The H+ gradient – Referred to as a proton-motive force • Emphasizes its capacity to do work
73
NADH and FADH2 shuttle high-energy electrons to an | electron transport chain
-Built into the inner mitochondrial membrane – Electrons extracted from food • During glycolysis and the citric acid cycle
74
Gold Arrow
Trace the transport of electrons • Finally pass to oxygen at the “downhill” end of the chain • Forming water
75
• Most of the electrons
``` – Grouped into 4 complexes • Two mobile carriers – Ubiquinone (Q) – Cytochrome C (Cyt C) – Move electrons between the large complexes ```
76
Complexes I, III, and IV accept and then donate | elctrons
– Pump protons from the mitochondrial matrix into the intermembrane space – FADH2 deposits its electrons via complex II • Fewer protons being pumped compared to NADH
77
Chemical energy
--Transformed into a proton-motive force | • A gradient of H+ across the membrane
78
Electron transfer in the electron | transport chain
Causes proteins to pump H+ from the mitochondrial matrix to the intermembrane space
79
H+ then moves back across the | membrane
Pass through channels in ATP synthase
80
ATP synthase
Uses the exergonic flow of H+ to drive phosphorylation of ATP

Biology 100 (7 decks)

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