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A level Biology AQA > Biological Molecules > Flashcards

Biological Molecules Flashcards

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1
Q

What elements are common to all the molecules of life?

A

Carbon, Hydrogen and Oxygen

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2
Q

What are the four main groups of carbon based molecules common to all life forms?

A

Carbohydrates, Lipids, Proteins and Nucleic Acids

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3
Q

Which molecule forms part of the plasma membrane?

A

Phospholipids

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4
Q

Which biological molecule forms proteins?

A

Amino acids (and nucleic acids)

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5
Q

Which two biological molecules are the main respiratory substrates?

A

Lipids and Carbohydrates

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6
Q

What is a polymer?

A

A series of repeating units (monomers) joined together

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7
Q

What reaction joins two monomers together?

A

Condensation reaction

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8
Q

What reaction breaks down polymers?

A

Hydrolysis

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9
Q

What type of chemical bond is formed between monomers?

A

Covalent bond

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10
Q

Why is it known as a condensation reaction?

A

A molecule of water is produced/released

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11
Q

Describe the process of hydrolysis

A

A water molecule is used to break a covalent bond. An H and an OH group are joined to the monomers.

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12
Q

What type of reaction joins monosaccharides together?

A

Condensation reaction

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13
Q

What is a disaccharide and what is the bond involved?

A

Two monosaccharides joined together by a glycosidic bond

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14
Q

What type of reaction breaks down disaccharides?

A

Hydrolysis

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15
Q

What disaccharide is made by joining two glucose molecules?

A

Maltose

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16
Q

What disaccharide is made by joining fructose and glucose?

A

Sucrose

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17
Q

What disaccharide is made by joining glucose and galactose?

A

Lactose

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18
Q

What are the 3 types of polysaccharides that alpha-glucose can form?

A

-Amylose
-Amylopectin
-Glycogen

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19
Q

What type of reaction breaks polysaccharides apart?

A

Hydrolysis

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20
Q

Describe the structure of glycogen

A

Polymer of alpha-glucose it is highly branched

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21
Q

State the two structures that make up starch

A

Amylopectin and Amylose

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22
Q

Describe the structure and properties of starch

A

A mixture of two polysaccharides of alpha glucose. Amylose is a long branched chain of alpha glucose. The angles of the glycosidic bonds give it a coiled structure which makes it compact so it is good for storage. Amylopectin is a long branched chain of a glucose. Its side branches allow enzymes to get at the glycosidic bonds easily so glucose can be released quickly. It is insoluble in water

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23
Q

What’s the differences and similarities between starch and glycogen?

A

Glycogen is always branched, starch isn’t. Starch is found in plants, glycogen in animals. Both are energy stores, both made of alpha glucose.

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24
Q

How are the monosaccharides in cellulose arranged?

A

Alternative β-glucose molecules are turned upside down

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25
Q

Why are different enzymes needed to digest starch and cellulose?

A

Different shape molecule requires a different enzyme as they have different active site shapes. Cellulose is made of β-glucose and starch of α-glucose. 1,6 glycosidic bonds are only in starch. Starch is made of amylose and amylopectin, cellulose is linear and starch is branched

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26
Q

Based on the arrangement of cellulose molecules, explain why cell walls provide strength and support to plant cells.

A

-Cellulose molecules form hydrogen bonds with each other to make microfibrils
-Fibres are tough and flexible

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27
Q

1,6 glycosidic bonds are found on…

A

Amylopectin and Glycogen

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28
Q

β-glucose can be found only in…

A

Cellulose

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29
Q

Describe the structure of amylopectin, including the bonds involved and the shape

A

Amylopectin is a long branched chain of glucose. Its side branches, 1,4 and 1,6 glycosidic bonds, branched

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30
Q

What type of reaction joins nucleotides?

A

Condensation

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31
Q

What is semi conservative replication?

A

Half of the strands in each new DNA molecule are from the original DNA molecule

32
Q

Why is it known as semi conservative replication?

A

Because the original strand is split in two and half of each strand comes from the original, half is conserved

33
Q

What evidence do we have to prove there is two strands?

A

the Meselson and Stahl experiment

34
Q

What enzyme breaks the hydrogen bonds between the bases?

A

DNA helicase

35
Q

What enzyme adds new nucleotides to the new strand?

A

DNA polymerase

36
Q

Why is one strand known as the template strand?

A

because it acts as a template for new nucleotides to create a new strand with the correct complimentary base pairing

37
Q

State the enzymes involved in DNA replication

A

DNA helicase, DNA polymerase

38
Q

Which enzyme separates the strands in DNA replication?

A

DNA helicase

39
Q

State the role of DNA polymerase

A

joins nucleotides together in condensation reactions

40
Q

State the steps of DNA replication in order

A
  1. DNA helicase separates the two strands by breaking the hydrogen bonds between bases
  2. Each strands acts as a template
  3. Free nucleotides attach to template strand through complementary base pairing
  4. DNA polymerase joins nucleotides by reforming hydrogen bonds between bases
  5. Replication is semi conservative as new DNA molecules contain one old strand and one new strand
41
Q

The free nucleotides pair up with the exposed bases on the DNA strands based on which principle?

A

complementary base pairing

42
Q

Name the 4 bases found in DNA, name the bond that form between them

A

Adenine - thymine (2 hydrogen bonds) Guanine - cytosine (3 hydrogen bonds)

43
Q

Which molecules make up the backbone of a polynucleotide?

A

Phosphates and pentose/ribose sugars

44
Q

Describe the difference between bacterial DNA and eukaryotic DNA

A

bacterial DNA is short, circular and not associated with proteins. Eukaryotic DNA is long, linear and associated with proteins to form chromosomes

45
Q

What are the four differences between DNA and RNA?

A

thymine + uracil, deoxyribose + ribose, double stranded + single stranded, long strand + short strand

46
Q

What is the structure of ATP?

A

it contains a ribose sugar, an adenine base but has three phosphate groups

47
Q

What does the hydrolysis of ATP produce?

A

ADP + Pi

48
Q

Give the equation for the formation of ATP

A

ADP + Pi = ATP (reversible reaction)

49
Q

What are the differences between ATP and a DNA nucleotide?

A

ATP contains two more phosphate groups and is only made of adenine bases, DNA can have 4 different bases

50
Q

State four roles of lipids

A

Source of energy, waterproofing, insulation, protection

51
Q

What does a triglyceride consist of?

A

Glycerol and 3 fatty acids

52
Q

What bonds hold a triglyceride together?

A

Ester bonds

53
Q

How is a phospholipid different to a triglyceride and how is it similar?

A

Only 2 fatty acids, a phosphate head. Both have fatty acids

54
Q

How many water molecules are needed when breaking down a triglyceride?

A

3

55
Q

What is the term for the reaction that forms lipids?

A

Condensation reaction

56
Q

Describe how phospholipids can form a bilayer arrangement

A
  • Hydrophilic heads point outwards
  • Hydrophobic tails point inwards
57
Q

State the monomer of a protein

A

amino acids

58
Q

What are the components that make up an amino acid?

A

central carbon - H atom - amine group - carboxyl group

59
Q

What part of the amino acid is variable and how many types are there?

A

R group - 20

60
Q

Name the bond formed between two amino acids

A

peptide bond

61
Q

What is the primary structure of a protein?

A

amino acid sequence

62
Q

What is the secondary structure of a protein?

A

alpha helix + beta pleated sheets

63
Q

What is the tertiary structure of a protein?

A

folding into a 3D shape

64
Q

What is the quaternary structure of a protein?

A

binding with other subunits

65
Q

State the bonds in a secondary protein

A

Hydrogen bonds

66
Q

State the bonds in the tertiary structure of proteins

A

Ionic, hydrogen, disulphide bridges

67
Q

Name the reaction that breaks down proteins

A

hydrolysis

68
Q

Why does increasing the temperature of a reaction increase the rate of reaction?

A

as temperature increases so does the rate of reaction because there is more kinetic energy so the molecules move faster increasing the number of collisions and therefore the number of ES-complexes formed

69
Q

If you were to increase the concentration of substrate in a reaction but the rate of reaction did not increase, what would you suggest is the limiting factor?

A

enzyme concentration

70
Q

How can the pH affect the rate of an enzyme controlled reaction?

A

Above and below the optimum pH for each enzyme the H+ ions and OH- ions disrupt the ionic and hydrogen bonds holding the enzymes tertiary structure in place.
At extremes of pH the active site changes shape and no more ES-complexes can be formed as the substrate no longer fits. The enzyme is permanently denatured, the reaction stops.

71
Q

Describe the test for a reducing sugar and state the positive result

A

add benedict’s reagent, heat
positive result= turns from blue to orange/brown

72
Q

What can be done if the test for a reducing sugar produces an negative result but sugars should be present?

A

Take another sample, add HCl and heat in water bath, then add NaOH to neutralise. Add benedict’s then heat

73
Q

Why is the benedict’s test known as a semi-quantitative test

A

because it tells you how much sugar there is but not exactly how much (not fully quantitative

74
Q

How can we use a colorimeter to do a quantitative benedict’s test?

A

-Colorimeters measure the absorbance or transmission of light by a coloured solution
-More concentrated solution, more light absorbed/less light transmitted
-Compare to data table (known concentrations vs abs/trans value)

75
Q

Describe the test for starch and state the positive result

A

add iodine solution, if starch is present it will change from orange/brown to blue/black

76
Q

Describe the test for protein and state the positive result

A

add biuret solution, if proteins are present then the solution will turn from blue to purple

77
Q

Describe the test for lipids and state the positive result

A

mix the sample with ethanol, mix solution with water then shake,
white emulsion layer forms if a lipid is present

A level Biology AQA (2 decks)

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