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A-Level Biology > Biological Molecules > Flashcards

Biological Molecules Flashcards

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1
Q

Define monomer. Give some examples

A
  • Smaller units that join together to form larger molecules.
  • E.g. monosaccharides, amino acids, nucleotides.
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2
Q

Define polymer. Give some examples

A
  • Molecules formed when many monomers join together.
  • E.g. polysaccharides, proteins, DNA/RNA
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3
Q

What happens in a condensation reaction?

A

A chemical bond forms between 2 molecules & a molecule of water is produced.

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4
Q

What happens in a hydrolysis reaction?

A

A water molecule is used to break a chemical bond between 2 molecules.

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5
Q

Name the 3 hexose monosaccharides

A

Glucose, fructose, galactose

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6
Q

Name 2 disaccharides. Describe how they form.

A
  1. Maltose: glucose + glucose
  2. Sucrose: glucose + fructose
  3. Lactose: glucose + galactose
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7
Q

Describe the structure and functions of starch.

A
  • Storage polymer of alpha-glucose in plant cells.
  • Insoluble = no osmotic effect
  • large = does not diffuse out of cells
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8
Q

Describe the structure and functions of glycogen

A
  • Main storage polymer of alpha-glucose in animals
  • Branched = many terminal ends for hydrolysis
  • Insoluble = no osmotic effect and does not diffuse out of cells
  • Compact
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9
Q

Describe the structure and function of cellulose

A
  • Straight-chain, unbranched molecule
  • H-bond crosslinks between parallel strands form microfibrils = high tensile strength.
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10
Q

Describe the benedict’s test for reducing sugars

A
  1. Add and equal volume of Benedict’s reagent to a sample.
  2. Heat the mixture in an electric water bath at 100 degrees for 5 mins.
  3. Positive result: colour change from blue to orange & brick-red precipitate forms.
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11
Q

Describe the Benedict’s test for non-reducing sugars

A
  1. Negative result: Benedict’s reagent remains blue
  2. Hydrolyse non-reducing sugars by adding 1cm-cubed of HCl. Heat in a boiling water bath for 5 mins.
  3. Neutralise the mixture using sodium carbonate solution.
  4. Proceed with Benedict’s test as usual.
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12
Q

Describe the test for starch

A
  1. Add iodine solution
  2. Positive result: colour change from orange to blue-black
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13
Q

Describe how to test for lipids in a sample

A
  1. Dissolve solid samples in ethanol
  2. Add an equal volume of water and shake.
  3. Positive result: milky white emulsion forms
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14
Q

How do triglycerides form?

A

Condensation reaction between 1 molecule of glycerol & 3 fatty acids forms ester bonds.

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15
Q

Relate the structure of triglycerides to their functions

A
  • High energy: mass ratio = high calorific value from oxidation.
  • Insoluble hydrocarbon chain = no effect on water potential
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16
Q

Compare phospholipids and triglycerides

A
  • Both have glycerol backbone
  • Both may be attached to fatty acids
  • Both contain the elements, C,H,O
  • Both formed by condensation reactions.
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17
Q

Are phospholipids and triglycerides polymers?

A

No. They are macromolecules.

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18
Q

Are phospholipids and triglycerides polymers?

A

No. They are macromolecules.

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19
Q

Why is water a polar molecule?

A

O is more electronegative than H, so attract the pair of electrons in the covalent bond more easily.

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20
Q

State 4 important properties of water

A
  1. Metabloite/solvent for chemical reactions in the body
  2. High specific heat capacity
  3. High latent heat of vapourisation
  4. Cohesion between molecules
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21
Q

Explain why water is significant to living organisms

A
  • Solvent for polar molecules during metabolic reactions.
  • Enables organisms to avoid fluctuations in core temperature.
  • Cohesion-tension of water molecules in transpiration stream.
22
Q

What are inorganic ions and where are they found in the body?

A
  • Ions that do not contain carbon atoms
  • Found in cytoplasm & extracellular fluid
  • May be in high or very low concentrations
23
Q

Explain the role of hydrogen ions in the body

A
  • High concentration of H+ = low pH.
  • H+ ions interact with H-bonds & ionic bonds in tertiary structure of proteins, which can cause them to denature
24
Q

Explain the role of iron ions in the body

A
  • Fe2+ bonds to porphyrin ring to form haem group in haemoglobin.
  • Haem group has binding site to transport 1 molecule of O2 around body in bloodstream.
  • 4 haem groups per haemoglobin molecule.
25
Q

Explain the role of sodium ions in the body

A

Involved in co-transport for absorption of glucose & amino acids in lumen of gut.

26
Q

Explain the role of sodium ions in the body

A

Involved in co-transport for absorption of glucose & amino acids in lumen of gut.

27
Q

Explain the role of phosphate ions in the body

A

DNA
ATP

28
Q

What is the general structure of an amino acid?

A

-COOH (carboxyl) group
-R variable side group
-NH2 (amine) group

29
Q

Describe how to test for proteins in a sample

A
  1. Add equal volume of sodium hydroxide to sample at room temperature.
  2. Add drops of dilute copper (II) sulfate solution. Swirl to mix.
  3. Positive result: colour changes from blue to purple
30
Q

How many amino acids are there and how do they differ from one another?

A

20
differ by R group

31
Q

How many levels of protein structure are there?

A

4

32
Q

Define the primary structure of a protein

A
  • Sequence, number & type of amino acids in the polypeptide
  • Determined by sequence of codons on mRNA
33
Q

Define secondary structure of a protein

A

Hydrogen bonds form between O attached to -C=O& H attached to -NH

34
Q

Describe the 2 types of secondary protein structure

A

Alpha-helix

35
Q

Describe the 2 types of secondary structure

A

Alpha-helix
* all N-H bonds on same side of protein chain
* spiral shape
* H-bonds parallel to helical axis

Beta-pleated sheet:
*N-H and C=O groups alternate from one side to the other.

36
Q

Define tertiary structure of a protein. Name the bonds present

A

3D structure formed by further folding of polypeptide

Bonds: disulfide bridges, ionic bonds, hydrogen bonds

37
Q

Describe the structure and function of globular proteins

A

Spherical and compact

Hydrophilic R groups face outwards & hydrophobic R groups face inwards

Involved in metabolic processes

38
Q

What are enzymes

A

Biological catalysts

Specific tertiary structure determines shape of active site. Complementary to specific substrate.

Formation of enzyme-substrate (ES) complexes lowers activation energy.

39
Q

Explain the induced fit model of enzyme action

A

Shape of active site is not directly complementary to substrate & is flexible.

Conformational change enables (ES) complexes to form.

This puts strain on substrate bonds, lowering activation energy.

40
Q

What is in a nucleotide?

A

Phosphate group, pentose sugar, base

41
Q

Name the pentose sugar in DNA & RNA

A

DNA: deoxyribose
RNA: ribose

42
Q

State the role of DNA in living cells

A

Base sequence of genes codes for functional RNA & amino acid sequence of polypeptides.

Genetic information determines inherited characteristics = influences structure & function of organisms.

43
Q

State the role of RNA in living cells

A

mRNA: Complementary sequence to 1 gene from DNA with introns (non-coding regions) spliced out. Codons can be translated into a polypeptide by ribosomes.

rRNA: component of ribosomes

tRNA: supplies complementary amino acids to mRNA codons during translation

44
Q

How do polynucleotides form?

A

Condensation reactions between nucleotides form strong phosphodiester bonds (sugar-phosphate backbone)

45
Q

Describe the structure of DNA

A

Double helix of 2 polynucleotide strands

H-bonds between complementary bases (A-T & C-G)

46
Q

Relate the structure of DNA to its functions

A

Sugar-phosphate backbone & many H-bonds provide stability

Long molecule stores lots of information

Helix is compact for storage in nucleus

base sequence of triplets codes for amino acids

double stranded for semi-conservative replication

complementary base pairing for accurate replication

weak H-bonds break so strands separate for replication

47
Q

Describe the structure of mRNA

A

Long ribose polynucleotide (shorter than DNA)

Contains U instead of T

Single stranded

48
Q

Describe the structure of tRNA

A

Single stranded of about 80 nucleotides

Folded into clover shape

Anticodon on one end, amino acid binding site on the other

49
Q

Why is DNA replication described as semiconservative?

A

Strands of DNA molecule act as a template

New DNA molecule contains 1 old strand and 1 new strand

50
Q

Outline the process of semiconservative replication

A

1.DNA helicase breaks H-bonds between base pairs
2. Each strand acts as a template
3. Free nucleotides from nuclear sap attach to exposed bases by complementary base pairing
4. DNA polymerase catalyses condensation reactions that join adjacent nucleotides on new strand
5. H-bonds reform.

A-Level Biology (8 decks)

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