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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
Describe “alpha helix”
- H bonds form with 1 peptide chain - bonds form every 4th amino acid - basis of globular proteins
26
Describe “beta pleated sheet”
- H bonding between 2 parallel chains - used for structural proteins (e.g. keratin)
27
What bonds can form in tertiary and quaternary structured proteins?
- weak interaction (e.g. hydrophobic or hydrophilic interactions) - hydrogen bonds - ionic bonds (> H bonds) -disulphide bonds (covalent and strongest between R groups containing sulphur)
28
Describe “quaternary structure”
Occurs in proteins that have more than 1 type of polypeptide chain working together, each polypeptide is referred to as a subunit
29
Describe “globular protein”
- round or spherical - water soluble as hydrophilic components are on the outside - enzymes, transport proteins (e.g. albumin), messenger proteins (e.g. hormones)
30
Describe “conjugated protein”
Contain non protein prosthetic group e.g. haemoglobin has 4 haem groups (iron)
31
Describe “further conjugated protein”
Conjugated proteins combine with lipids or carbohydrates: - lipoprotein is combination with lipid - glycoprotein is combination with carbohydrate
32
Describe “fibrous protein”
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
Define “non-overlapping”
Each base is only part of one triplet/codon, and each triplet/codon codes just one amino acid
34
Define “degenerate”
More than one triplet code for an amino acid
35
What is the name of the strand being transcripted?
Antisense strand
36
Define “translation”
The process in which ribosomes in the cytoplasm or endoplasmic reticulum synthesise proteins
37
Function of mRNA?
Carries the message of DNA from the nucleus to the cytoplasm
38
Describe “tRNA”
- single stranded - cloverleaf shape - two attachment sites - one end has site for amino acid - other end has site for anti-codons
39
Describe “ribosome”
- site of protein synthesis - formed from RNA and proteins
40
Define “polysome”
Many ribosomes can travel along the mRNA at the same time
41
Types of lipids?
- triglyceride - phospholipid - sterol
42
What type of molecules are lipids?
Macromolecules (large complex)
43
General structure of triglyceride?
1 glycerol backbone and 3 fatty acid chains, connected by ester bonds
44
Describe the formation of ester bond in triglycerides
- glycerol and fatty acids contain hydroxyl group (OH) - the hydroxyl groups interact - leading to formation of 3 water molecules - reaction is called **esterification**
45
In what ways can fatty acids vary?
- length of hydrocarbon chain - saturated/unsaturated
46
What does “saturated” mean?
Contains the greatest possible number of hydrogen atoms , without carbon-carbon double or triple bonds
47
What does “unsaturated” mean?
Contains 1 or more double bond between carbon atoms (causes the molecule to bend)
48
Difference between cis and trans fats?
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
Functions of triglycerides?
- 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
General structure of phospholipid?
1 glycerol attached to 2 fatty acid chains (1 saturated and 1 unsaturated) and 1 phosphate ion
51
Define “amphipathic”
Contains both hydrophobic and hydrophilic properties
52
Why do phospholipids contain 1 saturated and 1 unsaturated fatty acid each?
Gives membrane fluidity
53
Describe “sterol”
- aka steroids - based on a carbon ring structure - amphipathic
54
Functions of cholesterol?
- major component of cell membrane - gives cell membrane fluidity and stability
55
Function of carbohydrates?
- energy sources - structural materials
56
Examples of monosaccharides?
- glucose - fructose - galactose
57
Difference between alpha and beta glucose?
Alpha has the OH group at the bottom at 1’ but beta has the OH group on top at 1’
58
How are monosaccharides bonded together?
In a condensation reaction to form **glycosidic bonds**
59
Structure of maltose?
- formed from 2 glucose - alpha 1-4 glycosidic bond
60
Structure of sucrose (table sugar)?
- formed from glucose and fructose - alpha 1-2 glycosidic bond
61
Structure of lactose (milk sugar)?
- formed from galactose and glucose - beta 1-4 glycosidic bond
62
Describe “starch”
- storage molecule found in plants - made of *amylose* and *amylopectin* - large molecule - insoluble
63
Structure of amylose?
- 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
Structure of amylopectin?
- polymer of glucose joined by 1-4 glycosidic bond - has a branch every 20-30 glucose molecule - branch is 1-6 glycosidic bond
65
Describe “glycogen”
- 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
Describe “cellulose”
- structural - used in cell walls - made of beta glucose - strong and insoluble - every 2nd beta glucose is inverted
67
Steps of forming structure by cellulose?
1. Cellulose chain 2. Microfibril 3. Macrofibril 4. Cellulose fibre
68
Define “synthesis”
The building of large complex molecules from smaller molecules
69
Define “transport”
Pumping molecules or ions across membrane by active transport
70
Define “movement”
Protein muscle fibres in muscle cell contract
71
Describe “adenosine triphosphate”
- a store of chemical potential energy - molecules are hydrolysed to release chemical energy
72
Structure of ATP?
Adenine: nitrogenous base Ribose: pentose sugar 3 phosphate groups: inorganic phosphate
73
How does ATP release energy?
- 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
Properties of ATP?
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
Describe “reducing sugar”
- a sugar that serves as a reducing agent - has a free aldehyde (CH=O) or ketone (C=O) functional group
76
How can Benedict’s solution be used to assess reducing sugar content in solutions?
- qualitative - semi-quantitative - quantitative
77
What chemicals are used in a test for non-reducing sugars?
- hydrochloric acid (HCl) - sodium hydrogen carbonate (NaHCO3)
78
What chemicals make up Biuret reagent?
- sodium hydroxide (NaOH) - hydrated copper sulfate (CuSO4)

A-level Biology (7 decks)

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