Chapter 1 - The Chemical Basis of Life (3) Flashcards

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1
Q

Functions of proteins

A
enzymes = mediate chemical reactions in organisms
structure = used as building material
hormones = released by glands to cause an effect elsewhere in the body
antibodies = produced by immune system which target pathogens for destruction
transport = pump molecules against a concentration gradient
recognition = identify cells to your immune system
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2
Q

Structure of proteins

A

highly organized, complex molecules
their structure is described using up to 4 different levels of scrutiny
1 has the smallest scope
4 has the largest scope

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3
Q

Primary structure

A

the order of amino acids
met, val, leu, ala, try
all amino acids have the same structure
20 different amino acids for each position in a protein allows for an almost infinite number of possible sequences
the variety leads to a diverse structural and functional importance

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4
Q

Alpha helix

A

a common, stable and strong helical arrangement
stabilized by hydrogen bonds between a carbonyl oxygen and the amide hydrogen four amino acids down the chain
R-groups project outward from helix
the ends are created due to L-proline, which makes the structure very stiff
eg. keratin

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5
Q

Beta-pleated sheet

A

different sections of a polypeptide lie side by side
stabilized by hydrogen bonds
adjacent R-groups alternately project above and below the sheet, and therefore do not get in the way of the structure
eg. silk

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6
Q

Tertiary structure

A

overall, complex structure of a polypeptide
maintained by intermolecular attractions
disulphide bridges between cysteines can link distant regions of a polypeptide
polar and charged R-groups are attracted by water and clump together in hydrophobic pockets, but are unable to associate with lipids in membranes
bulky R-groups distort secondary structures such as alpha-helices
the R-group of proline is bonded twice, the inflexibility disrupting alpha-helices

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7
Q

Protrusions and pockets

A
protrusions = allow protein to interact with complementary pocket of another protein
pockets = provide attachment points for prosthetic groups and coenzymes
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8
Q

Quaternary structure

A

interaction between polypeptide and either other polypeptide(s) or prosthetic group(s)
the forces holding subunits together are the same as those that cause tertiary structure
disulphide linkages
hydrophilic and hydrophobic interactions
hydrogen bonding between subunits

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9
Q

Fibrous proteins

A

typically rod shaped
alpha-keratin
found in hair, fingernails, wool
characterized by long polypeptide chains with an uninterrupted alpha helix
beta-keratin
found in spider webs and silk
secondary structures consists of beta pleated sheets

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10
Q

Globular proteins

A

typically fold into compact spherical or oblong forms
maximizes the number of hydrogen bonds with water
hemoglobin
consists of 4 globular subunits, each with a heme prosthetic group
binds oxygen in blood cells
myoglobin
single globular polypeptide with an associated heme subgroup
binds oxygen in muscle cells

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11
Q

Thermodynamics

A

the study of energy transformations
first law = energy cannot be created or destroyed, only converted from one form to another
second law = during energy conversions, some of the energy is lost as heat, which increases the entropy of the molecules in the universe

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12
Q

Second law of thermodynamics

A

making ice cubes increases the entropy of the universe
even though water molecules are more orderly in cubes, the energy used by the freezer wasted energy
this is why there is no such thing as a perpetual motion machine

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13
Q

Exergonic reactions

A

same as exothermic, but occur at body temperature, can use enzymes
overall net release of energy
reactants have less bond energy, but more potential energy than the products
self-sustaining reactions (energy released acts as activation energy for other reactions)
eg. respiration

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14
Q

Endergonic reactions

A

same as endothermic, but occur at body temperature
require an overall input of energy
reactants have more bond energy but less potential energy than the products
not self-sustaining (requires continuous activation energy)
eg. photosynthesis

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15
Q

Metabolism

A

catabolic reaction = breaks down larger molecules to smaller ones, exergonic
anabolic reaction = builds larger molecules from smaller ones, endergonic
metabolism = total sum of the catabolic and anabolic reactions

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16
Q

Role of enzymes

A

molecules often don’t react unless they are activated (generally with heat)
this is the activation energy
enzymes decrease the activation energy of chemical reactions so they can occur at body temperatures

17
Q

Lock and key model

A

enzymes have a unique 3D shape which is complementary to the shape of specific substrates
only the correct substrates bind to the active site of the enzyme
the enzyme flexes, stressing bonds and causing new ones to form
products leave the active site
some enzymes can also put things together

18
Q

Induced fit model

A

enzyme normally exists in an inactive form
as substrates bind to the active site, enzyme is induced to achieve optimal fit
since the active site is not exclusively configured until after induction, enzymes have the ability to bind to several substrates

19
Q

Competitive inhibition

A

caused by a molecule which is similar to the substrate

binds to the active site, preventing the substrate from binding

20
Q

Non-competitive inhibition

A

caused by the binding of a molecule to a region other than the active site of an enzyme
changes the shape of the active site, preventing the enzyme from functioning

21
Q

Allosteric regulation

A

form of non-competitive inhibition
consists of two or more subunits whose shapes can be altered by activators or inhibitors to allosteric sites
activator or substrate binds with the enzyme in active site, locking it in active form
inhibitor binds in allosteric site, locking it in inactive form

22
Q

Feedback inhibition - one enzyme

A

a product produced by an enzyme can inhibit its activity
when product is in abundance, it binds competitively with the active site
as the product is used up, it diffuses away and the enzyme is free to produce more product, maintaining the concentration
excess of product leads to a slow diffusion, acting as competitive inhibitor

23
Q

Feedback inhibition - metabolic pathway

A

the end product of the pathway binds at an allosteric site on the first enzyme of the pathway
this shuts down the entire pathway, minimizing the intermediate products

24
Q

Low temperature and enzyme activity

A

substrates diffuse into the active site very slowly
products diffuse away slowly, interfering entry of new substrates
enzyme is very stiff

25
Q

High temperature and enzyme activity

A

substrates diffuse into active site faster
products diffuse away faster
enzyme is more flexible

26
Q

Denaturation

A

at excessively high temperatures, the enzyme’s activity increases a lot
this affects the intermolecular attractions and disulphide bridges and the enzyme can no longer maintain its tertiary structure
the enzyme is denatured and rendered useless

27
Q

Lowering pH and enzyme activity

A

adds protons to neutral amino or charged carboxyl groups
previously neutral amino groups become positive
previous charged carboxyl groups become neutral

28
Q

Raising pH and enzyme activity

A

removes protons
charged amino groups become neutral
neutral carboxyl groups become charged

29
Q

pH and enzyme activity

A

altering the charge of the R-groups affects their intermolecular interactions with water and other parts of the enzyme
this therefore changes the tertiary structure of the enzyme
each enzyme has a different optimal pH

30
Q

Redox reactions

A

in metabolic processes, molecules or atoms often lose their high potential energy electrons to a different atom or molecule
the transfer of such excited electrons is called a redox reaction, as reductions and oxidations always happen together

31
Q

Electron donors and acceptors

A
electron donors = 
are oxidized in a redox reaction
are reducing agents
electron acceptors = 
are reduced in a redox reaction
are oxidizing agents
32
Q

Electron carriers

A
NADH = mitochondria, becomes NAD+
FADH2 = mitochondria, becomes FADH
NADPH = chloroplasts, becomes NADP