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A-level Biology > 3 Biological Molecules > Flashcards

3 Biological Molecules Flashcards

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1
Q

What reactions use water as a metabolite?

A
  • hydrolysis
  • condensation
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2
Q

Properties of water?

A
  • good solvent
  • relatively high specific heat capacity
  • relatively high latent heat of vaporisation
  • less dense as a solid
  • cohesive and adhesive
  • acts as reagent
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3
Q

Why can water form hydrogen bonds?

A

Due to the uneven electron affinity between hydrogen and oxygen atoms, so slight negative charge on oxygen atom attracts the slight positive charge on hydrogen atoms

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4
Q

Why is it important for water to be cohesive and adhesive?

A

Column of water does not break when water molecules are pulled up a narrow tube, so materials can be transported (e.g. cellulose)

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5
Q

Why is water less dense as a solid?

A

Water forms 4 H bonds with other H2O molecules at low temperatures, forming a lattice structure which expands resulting in the lower density of ice; this forms an insulating layer for aquatic animals as ice floats

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6
Q

Why is water a good solvent important?

A

Many ions and covalent polar substances can dissolve in water, which allows chemical reactions to occur in cells; also metabolites can be transported in blood efficiently when water acts as transport medium

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7
Q

Why is water having a relatively high SHC important?

A

Water absorbs/loses relatively large amount of heat before temperature change, which makes it able to maintain a constant temperature without big temperature fluctuations; so it provides stable habitats and is vital in maintaining temperatures that are optimal for enzyme activity

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8
Q

Why is water having relatively high LH of vaporisation important?

A

Water absorbs large amount of energy before turning into water vapour, as large amount of thermal energy is needed to break H bonds and evaporate, so only little water is required to evaporate for an organism to lose a great amount of heat

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9
Q

What are the biological roles of protein?

A
  • structural
  • catalytic
  • signalling
  • immunological
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10
Q

What is the general structure of an amino acid?

A
  • amine group (NH2)
  • carboxyl group (COOH)
  • hydrogen atom (H)
  • R group (variable side chain)
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11
Q

What bonds form in polypeptide?

A

Peptide bonds (–CO–NH–) are covalent bonds

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12
Q

Describe the formation of a peptide bond

A
  • covalent bond formed via a condensation reaction
  • hydrogen from amine group of 1 amino acid reacts with hydroxyl from the carboxyl group of an adjacent amino acid
  • resulting in formation of water and a peptide bond
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13
Q

Describe DNA

A
  • the genetic code which makes up genes
  • exist as double strand helix
  • contains 4 bases
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14
Q

3 chemical groups in a nucleotide?

A

Phosphate group
- inorganic chemical
- negatively charged

Nitrogenous base
- different nitrogen bases that make up the five different nucleotides

Pentose monosaccharide (sugar)
- DNA has deoxyribose sugar
- RNA has ribose sugar

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15
Q

How are nucleotides joined together?

A

Phosphodiester bonds between phosphate group and pentose sugar

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16
Q

What are the nitrogenous bases?

A
  • adenine
  • cytosine
  • guanine
  • thymine (only in DNA)
  • uracil (only in RNA)
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17
Q

Define “codon”

A

A DNA or RNA sequence of 3 nucleotides that encodes a particular amino acid

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18
Q

What are pyrimidines and purines?

A

Pyrimidine: 1 carbon ring (C, T, U)
Purine: 2 carbon rings (A, G)

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19
Q

What is semi-conservative replication?

A

Each new DNA molecule has one DNA strand from the original DNA molecule, which ensures genetic continuity and all genes are inherited by new cell

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20
Q

What are the enzymes involved in DNA replication?

A

DNA helicase:
travels along DNA backbone unwinds DNA and breaks H bonds between base pairs

DNA polymerase:
Catalyses the formation of phosphodiester bonds between free nucleotides which pair with DNA (only in 5’ to 3’ direction)

DNA ligase:
Joins the lagging strand segments together by phosphodiester bonds

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21
Q

What are the steps of DNA replication?

A
  1. Unwinding
    DNA helicase unwinds the DNA double helix by breaking H bonds between the base pairs on the two antiparallel strands
  2. Base pairing
    As the two strands separate activated nucleotides join with complementary base pairs and H bonds form
  3. Backbone
    The new nucleotides are joined by DNA polymerase which catalyses condensation reactions to form phosphodiester bonds of new strand
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22
Q

What is the primary structure of a protein determined by?

A

DNA sequence to form a simple polypeptide chain

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23
Q

How are secondary structured proteins formed?

A

Oxygen, hydrogen and nitrogen in the amino acids interact to form hydrogen bonds which folds the protein

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24
Q

What are the 2 types of secondary structure?

A

Alpha helix and Beta pleated sheet

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25
Q

Describe “alpha helix”

A
  • H bonds form with 1 peptide chain
  • bonds form every 4th amino acid
  • basis of globular proteins
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26
Q

Describe “beta pleated sheet”

A
  • H bonding between 2 parallel chains
  • used for structural proteins (e.g. keratin)
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27
Q

What bonds can form in tertiary and quaternary structured proteins?

A
  • weak interaction (e.g. hydrophobic or hydrophilic interactions)
  • hydrogen bonds
  • ionic bonds (> H bonds)
    -disulphide bonds (covalent and strongest between R groups containing sulphur)
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28
Q

Describe “quaternary structure”

A

Occurs in proteins that have more than 1 type of polypeptide chain working together, each polypeptide is referred to as a subunit

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29
Q

Describe “globular protein”

A
  • round or spherical
  • water soluble as hydrophilic components are on the outside
  • enzymes, transport proteins (e.g. albumin), messenger proteins (e.g. hormones)
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30
Q

Describe “conjugated protein”

A

Contain non protein prosthetic group e.g. haemoglobin has 4 haem groups (iron)

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31
Q

Describe “further conjugated protein”

A

Conjugated proteins combine with lipids or carbohydrates:
- lipoprotein is combination with lipid
- glycoprotein is combination with carbohydrate

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32
Q

Describe “fibrous protein”

A

Structural and insoluble:
- keratin provides structure to hair and nails
- collagen is a type of connective tissue in the body
- elastin are found in elastic fibres (e.g. alveoli or blood vessels)

33
Q

Define “non-overlapping”

A

Each base is only part of one triplet/codon, and each triplet/codon codes just one amino acid

34
Q

Define “degenerate”

A

More than one triplet code for an amino acid

35
Q

What is the name of the strand being transcripted?

A

Antisense strand

36
Q

Define “translation”

A

The process in which ribosomes in the cytoplasm or endoplasmic reticulum synthesise proteins

37
Q

Function of mRNA?

A

Carries the message of DNA from the nucleus to the cytoplasm

38
Q

Describe “tRNA”

A
  • single stranded
  • cloverleaf shape
  • two attachment sites
  • one end has site for amino acid
  • other end has site for anti-codons
39
Q

Describe “ribosome”

A
  • site of protein synthesis
  • formed from RNA and proteins
40
Q

Define “polysome”

A

Many ribosomes can travel along the mRNA at the same time

41
Q

Types of lipids?

A
  • triglyceride
  • phospholipid
  • sterol
42
Q

What type of molecules are lipids?

A

Macromolecules (large complex)

43
Q

General structure of triglyceride?

A

1 glycerol backbone and 3 fatty acid chains, connected by ester bonds

44
Q

Describe the formation of ester bond in triglycerides

A
  • glycerol and fatty acids contain hydroxyl group (OH)
  • the hydroxyl groups interact
  • leading to formation of 3 water molecules
  • reaction is called esterification
45
Q

In what ways can fatty acids vary?

A
  • length of hydrocarbon chain
  • saturated/unsaturated
46
Q

What does “saturated” mean?

A

Contains the greatest possible number of hydrogen atoms , without carbon-carbon double or triple bonds

47
Q

What does “unsaturated” mean?

A

Contains 1 or more double bond between carbon atoms (causes the molecule to bend)

48
Q

Difference between cis and trans fats?

A

Cis fatty acids have H atoms on the same side of the double bond which can be metabolised by enzymes.

Trans fatty acids has H atoms on opposite sides of the double bond, which cannot form enzyme-substrate complex so cannot be metabolised

49
Q

Functions of triglycerides?

A
  • energy storage
  • releases metabolic water and energy used to produce ATP
  • electric or heat insulation
  • buoyancy due to low density
  • protection by surrounding organs to reduce risk of damage
50
Q

General structure of phospholipid?

A

1 glycerol attached to 2 fatty acid chains (1 saturated and 1 unsaturated) and 1 phosphate ion

51
Q

Define “amphipathic”

A

Contains both hydrophobic and hydrophilic properties

52
Q

Why do phospholipids contain 1 saturated and 1 unsaturated fatty acid each?

A

Gives membrane fluidity

53
Q

Describe “sterol”

A
  • aka steroids
  • based on a carbon ring structure
  • amphipathic
54
Q

Functions of cholesterol?

A
  • major component of cell membrane
  • gives cell membrane fluidity and stability
55
Q

Function of carbohydrates?

A
  • energy sources
  • structural materials
56
Q

Examples of monosaccharides?

A
  • glucose
  • fructose
  • galactose
57
Q

Difference between alpha and beta glucose?

A

Alpha has the OH group at the bottom at 1’ but beta has the OH group on top at 1’

58
Q

How are monosaccharides bonded together?

A

In a condensation reaction to form glycosidic bonds

59
Q

Structure of maltose?

A
  • formed from 2 glucose
  • alpha 1-4 glycosidic bond
60
Q

Structure of sucrose (table sugar)?

A
  • formed from glucose and fructose
  • alpha 1-2 glycosidic bond
61
Q

Structure of lactose (milk sugar)?

A
  • formed from galactose and glucose
  • beta 1-4 glycosidic bond
62
Q

Describe “starch”

A
  • storage molecule found in plants
  • made of amylose and amylopectin
  • large molecule
  • insoluble
63
Q

Structure of amylose?

A
  • unbranched polymer of alpha glucose
  • joined by 1-4 glycosidic bond
  • chain of amylose twists to form helix
  • H bonds formed between glucose molecules hold its shape
  • allows starch to be compact
64
Q

Structure of amylopectin?

A
  • polymer of glucose joined by 1-4 glycosidic bond
  • has a branch every 20-30 glucose molecule
  • branch is 1-6 glycosidic bond
65
Q

Describe “glycogen”

A
  • similar structure to amylopectin but has a more branched structure due to 1-6 glycosidic bonds
  • stored as compact granules in muscles and liver
  • insoluble
  • more dense and broken more rapidly
66
Q

Describe “cellulose”

A
  • structural
  • used in cell walls
  • made of beta glucose
  • strong and insoluble
  • every 2nd beta glucose is inverted
67
Q

Steps of forming structure by cellulose?

A
  1. Cellulose chain
  2. Microfibril
  3. Macrofibril
  4. Cellulose fibre
68
Q

Define “synthesis”

A

The building of large complex molecules from smaller molecules

69
Q

Define “transport”

A

Pumping molecules or ions across membrane by active transport

70
Q

Define “movement”

A

Protein muscle fibres in muscle cell contract

71
Q

Describe “adenosine triphosphate”

A
  • a store of chemical potential energy
  • molecules are hydrolysed to release chemical energy
72
Q

Structure of ATP?

A

Adenine: nitrogenous base
Ribose: pentose sugar
3 phosphate groups: inorganic phosphate

73
Q

How does ATP release energy?

A
  • energy is released when bonds are broken by hydrolysis reaction
  • ATP is resynthesized in condensation reactions
  • ATP is stored as fats and carbohydrates as ATP is relatively unstable
  • during cellular respiration fats and carbohydrates are broken down to make ATP
74
Q

Properties of ATP?

A

Small: easy to move about, in and out of cells

Water soluble: energy-requiring processes happen in aqueous environments

Contains bond between phosphates with intermediate energy: reduces amount of energy being wasted as heat

Releases energy in small quantities: quantities needed for cellular reactions, energy is not wasted

Easily regenerated: can be recharged with energy

75
Q

Describe “reducing sugar”

A
  • a sugar that serves as a reducing agent
  • has a free aldehyde (CH=O) or ketone (C=O) functional group
76
Q

How can Benedict’s solution be used to assess reducing sugar content in solutions?

A
  • qualitative
  • semi-quantitative
  • quantitative
77
Q

What chemicals are used in a test for non-reducing sugars?

A
  • hydrochloric acid (HCl)
  • sodium hydrogen carbonate (NaHCO3)
78
Q

What chemicals make up Biuret reagent?

A
  • sodium hydroxide (NaOH)
  • hydrated copper sulfate (CuSO4)

A-level Biology (7 decks)

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