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Biology 100 > Biology 203 (Exam 2) > Flashcards

Biology 203 (Exam 2) Flashcards

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AP® Biology flashcards Biology 101 flashcards
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
Q

A catalyst

A

A chemical agent that speeds up a reaction

• Without being consumed by the reaction

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26
Q

An enzyme

A

– A catalytic protein

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27
Q

Hydrolysis of sucrose by the

enzyme sucrase

A

An example of an enzymecatalyzed

reaction

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28
Q

Every chemical reaction

between molecules

A

Involves bond breaking and

bond forming

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29
Q

The initial energy needed to

start a chemical reaction

A

Activation energy (EA)

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30
Q

Activation energy

A

Often supplied in the form of heat from the

surroundings

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31
Q

Enzymes catalyze reactions

A

by

lowering the EA barrier

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32
Q

Enzymes do not affect the change

in free energy (ΔG)

A

Instead, they hasten reactions that would occur

eventually

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33
Q

The reactant that an enzyme acts on

A

– Called the enzyme’s substrate

34
Q

The enzyme binds to its substrate

A

Forming an enzyme-substrate complex

35
Q

The active site

A

The region on the enzyme where the substrate binds

36
Q

Induced fit of a substrate

A

－Brings chemical groups of the active site into positions

– Enhance their ability to catalyze the reaction

37
Q

In an enzymatic reaction

A

Substrate binds to the active

site of the enzyme

38
Q

The active site can lower an EA barrier by

A 
－Orienting substrates correctly
– Straining substrate bonds
– Providing a favorable
microenvironment
– Covalently bonding to the
substrate
39
Q

An enzyme’s activity can be

affected by

A

－General environmental factors,
such as temperature and pH
– Chemicals that specifically
influence the enzyme

40
Q

Effects of Temperature and pH

A 
－Each enzyme has an optimal temperature in which it can
function
– Each enzyme has an optimal pH in which it can function
41
Q

Cofactors

A 
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
Q

Enzyme Inhibitors

A

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
Q

Regulation of enzyme activity

A

Helps control metabolism

44
Q

Living cells require energy

from outside sources

A 
－Some animals, such as the
giant panda, obtain energy
by eating plants
– Some animals feed on
other organisms that eat
plants
45
Q

Energy flows into an ecosystem as sunlight

A

Leaves as heat

46
Q

Photosynthesis generates O2 and organic molecules

A

Used in cellular respiration

47
Q

Cells use chemical energy stored in organic molecules

A

－Regenerate ATP

• Powers work

48
Q

Stages of Cellular Repsiration

A Preview

A

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
Q

Cellular Respiration

A

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
Q

Redox Reactions: Oxidation and Reduction

A
  • The transfer of electrons during
    chemical reactions
    – Releases energy stored in organic
    molecules

• This released energy is ultimately
used to synthesize ATP

51
Q

The Principle of Redox (slide 6, ch10)

A 
--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
Q

Reducing Agents and Oxidizing Agents

A

*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
Q

During cellular respiration

A 
The fuel (such as glucose) is oxidized
–O2 is reduced
54
Q

Electron transport chain

A 
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
Q

Nicotinamide adenine

dinucleotide (NADH)

A

passes the
electrons to the electron
transport chain

56
Q

Niacin

A

Vitamin B3

57
Q

Pellagra

A

Vitamin deficiency disease

58
Q

Tradition food preparation of corn

A 
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
Q

In cellular respiration:

A

Glucose and other organic molecules are broken down in a series of steps

60
Q

Electrons from organic compounds are usually first transferred to NAD+

A

– A coenzyme

61
Q

NAD+ functions as an oxidizing agent during cellular respiration

A

NAD+ is an electron acceptor

62
Q

Each NADH (the reduced form of NAD+)

A

Represents stored energy

– Tapped to synthesize ATP

63
Q

Glycolysis

A 
“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
Q

Energy Investment

Phase

A 
Glucose enters the
cell
• Phosphorylated by
hexokinase
– Sugar trapped in
cell
– More chemically
reactive
– Transfer of a
phosphate group
• Investment
of energy
65
Q

Glycolisis: Energy Investment

Phase

A 
Glucose-6-phosphate
converted to its
isomer
• Fructose-6-
phosphate
66
Q

aerobic respiration takes place in about 20 steps, grouped into three stages:

A

1) Glycolysis
2) Formation of acetyl coenzyme A and the citric acid cycle (Krebs cycle)
3) The electron transport chain and chemiosmosis

67
Q

Cellular respiration has three stages:

A 
– 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
Q

Oxidative Phosphorylation

A

• 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
Q

During Oxidative Phosphorylation

A

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
Q

Chemiosmosis

A

Diffusion of ions across a selectively-permeable membrane

• Generation of ATP by the movement of hydrogen ions across a membrane during cellular respiration

71
Q

The Pathway of Electron Transport

A 
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
Q

Chemiosmosis Couples The Electron Transport

Chain to ATP Synthesis

A

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
Q

NADH and FADH2 shuttle high-energy electrons to an

electron transport chain

A

-Built into the inner mitochondrial membrane
– Electrons extracted from food
• During glycolysis and the citric acid cycle

74
Q

Gold Arrow

A

Trace the transport of electrons
• Finally pass to oxygen at the “downhill” end of
the chain
• Forming water

75
Q

• Most of the electrons

A 
– Grouped into 4 complexes
• Two mobile carriers
– Ubiquinone (Q)
– Cytochrome C (Cyt C)
– Move electrons between the large
complexes
76
Q

Complexes I, III, and IV accept and then donate

elctrons

A

– 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
Q

Chemical energy

A

–Transformed into a proton-motive force

• A gradient of H+ across the membrane

78
Q

Electron transfer in the electron

transport chain

A

Causes proteins to pump H+ from the mitochondrial matrix to the
intermembrane space

79
Q

H+ then moves back across the

membrane

A

Pass through channels in ATP synthase

80
Q

ATP synthase

A

Uses the exergonic flow of H+ to drive phosphorylation of ATP

Biology 100 (7 decks)

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