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biological molecules Flashcards

1
Q

What are monomers and polymers

A

● Monomers- smaller, repeating molecules / units from which larger molecules / polymers are made
● Polymers- molecules made from many (a large number) identical / similar monomer molecules

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2
Q

What happens in a condensation reaction

A

● 2 molecules join together
● Forming a chemical bond
● Releasing a water molecule

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3
Q

What happens in hydrolysis reactions

A

● 2 molecules separated
● Breaking a chemical bond
● Using a water molecule

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4
Q

Give examples of polymers and the monomers from which they’re made

A

Nucleotides —-> polynucleotide (DNA/RNA)
monosaccharide eg glucose —-> polysaccharide eg starch
Amino acid —-> polypeptide (protein)

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5
Q

What are monosaccharides? Give 3 common examples

A

● Monomers from which larger carbohydrates are made
● Glucose, fructose, galactose

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6
Q

Describe the difference between the structure of α-glucose and β-glucose

A

● Isomers- same molecular formula but differently arranged atoms
● OH group is below carbon 1 in α-glucose but above carbon 1 in β-glucose

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7
Q

What are disaccharides and how are they formed?

A

● Two monosaccharides joined together with a glycosidic bond
● Formed by a condensation reaction, releasing a water molecule

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8
Q

List 3 common disaccharides & monosaccharides from which they’re made

A

Maltose —> Glucose + glucose
Sucrose —-> Glucose + fructose
Lactose —-> Glucose + galactose

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9
Q

What are polysaccharides and how are they formed?

A

● Many monosaccharides joined together with glycosidic bonds
● Formed by many condensation reactions, releasing many water molecules

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10
Q

Describe the basic function and structure of starch and glycogen

A
  • Starch*
    Energy store in plant cells
    ● Polysaccharide of α-glucose
    ● Some has 1,4-glycosidic bonds so is unbranched (amylose)
    ● Some has 1,4- and 1,6-glycosidic bonds so is branched (amylopectin)
    glucogen Energy store in
    animal cell - polysaccharide made of alpha glucose 1,4 and 1,6 glycosidic bonds —
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11
Q

Explain how the structures of starch and glycogen relate to their functions

A

Starch (amylose)
● Helical → compact for storage in cell
● Large, insoluble polysaccharide molecule → can’t leave cell / cross cell membrane
● Insoluble in water → water potential of cell not affected (no osmotic effect)

Glycogen ( and starch/amylopectin)
● Branched → compact / fit more molecules in small area
● Branched → more ends for faster hydrolysis → release glucose for respiration to
make ATP for energy release
● Large, insoluble polysaccharide molecule → can’t leave cell / cross cell membrane
● Insoluble in water → water potential of cell not affected (no osmotic effect)

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12
Q

Describe the basic function and structure of cellulose

A

Function
● Provides strength and structural support to plant / algal cell walls
Structure
● Polysaccharide of β-glucose
1,4-glycosidic bonds so forms straight, unbranched chains
Chains linked in parallel by hydrogen bonds, forming microfibrils

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13
Q

Explain how the structure of cellulose relates to its function

A

● Every other β-glucose molecule is inverted in a
long, straight, unbranched chain
● Many hydrogen bonds link parallel strands
(crosslinks) to form microfibrils (strong fibres)
● Hydrogen bonds are strong in high numbers
● So provides strength to plant cell walls

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14
Q

Name 3 reducing sugars

A

Reducing sugars = monosaccharides, maltose, lactose

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15
Q

Describe the test for reducing sugars

A
  1. Add Benedict’s solution (blue) to sample
  2. Heat in a boiling water bath
  3. Positive result = green / yellow / orange / red precipitate
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16
Q

Name non-reducing sugars

A

Sucrose

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17
Q

Describe the test for non-reducing sugars

A
  1. Do Benedict’s test (as above) and stays blue / negative
  2. Heat in a boiling water bath with acid (to hydrolyse into reducing sugars)
  3. Neutralise with alkali (eg. sodium bicarbonate)
  4. Heat in a boiling water bath with Benedict’s solution
  5. Positive result = green / yellow / orange / red precipitate
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18
Q

Suggest a method to measure the quantity of sugar in a solution

A

● Carry out Benedict’s test as above, then filter and dry precipitate
● Find mass / weight

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19
Q

Suggest another method to measure the quantity of sugar in a solution

A

1.Make sugar solutions of known concentrations
(eg. dilution series)
2. Heat a set volume of each sample with a set
volume of Benedict’s solution for the same time
3. Use colorimeter to measure absorbance (of
light) of each known concentration
4. Plot calibration curve- concentration on x axis,
absorbance on y axis and draw line of best fit
5. Repeat Benedict’s test with unknown sample and
measure absorbance
6. Read off calibration curve to find concentration
associated with unknown sample’s absorbance

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20
Q

Describe the biochemical test for starch

A
  1. Add iodine dissolved in potassium iodide (orange / brown) and shake / stir
  2. Positive result = blue-black
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21
Q

Name two groups of lipid

A

Triglycerides and phospholipids

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22
Q

Describe the structure of a fatty acid (RCOOH)

A

● Variable R-group- hydrocarbon chain (this may be saturated or unsaturated)
●-COOH = carboxyl group

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23
Q

Describe the difference between saturated and unsaturated fatty acids

A

● Saturate- no C=C double bonds in hydrocarbon chain → all carbons fully saturated with hydrogen
● Unsaturated- one or more C=C double bond in hydrocarbon chain (creating a bend / kink)

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24
Q

Describe how triglycerides form

A

● 1 glycerol molecule and 3 fatty acids
● 3 condensation reactions
● 3 condensation reactions
● Removing 3 water molecules
● Forming 3 ester bonds

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25
Explain how the properties of triglycerides are related to their structure
Function: energy storage ● High ratio of C-H bonds to carbon atoms in hydrocarbon chain ○ So used in respiration to release more energy than the same mass of carbohydrates ● Hydrophobic / non-polar fatty acids so insoluble in water (clump together as droplets, tails inwards) ○ So no effect on water potential of cell (or can be used for waterproofing)
26
Describe the difference between the structure of triglycerides and phospholipids
One of the fatty acids of a triglyceride is substituted by a phosphate-containing group
27
Describe how the properties of phospholipids relate to their structure
Function: form a bilayer in cell membrane, allowing diffusion of lipid-soluble (non-polar) or very small substances and restricting movement of water-soluble (polar) or larger substances ● Phosphate heads are hydrophilic ○ Attracted to water so point to water (aqueous environment) either side of membrane ● Fatty acid tails are hydrophobic ○ Repelled by water so point away from water / to interior of membrane
28
Describe the test for lipids
1. Add ethanol, shake (to dissolve lipids), then add water 2. Positive result = milky white emulsion
29
Describe / draw the general structure of an amino acid
● COOH = carboxyl group ● R = variable side chain / group ● H2N = amine group Central carbon
30
How many amino acids are common in all organisms? How do they vary?
The 20 amino acids that are common in all organisms differ only in their side group (R)
31
Describe how amino acids join together
● Condensation reaction ● Removing a water molecule ● Between carboxyl / COOH group of one and amine / NH2 group of another ● Forming a peptide bond
32
What are dipeptides and polypeptides?
● Dipeptide- 2 amino acids joined together ● Polypeptide- many amino acids joined together
33
Describe the primary structure of a protein
Sequence of amino acids in a polypeptide chain, joined by peptide bond
34
Describe the secondary structure of a protein
● Folding (repeating patterns) of polypeptide chain eg. alpha helix / beta pleated sheets ● Due to hydrogen bonding between amino acids ● Between NH (group of one amino acid) and C=O (group)
35
Describe the tertiary structure of a protein
● 3D folding of polypeptide chain ● Due to interactions between amino acid R groups (dependent on sequence of amino acids) ● Forming hydrogen bonds, ionic bonds and disulfide bridges
36
Describe the quaternary structure of a protein
● More than one polypeptide chain ● Formed by interactions between polypeptides (hydrogen bonds, ionic bonds, disulfide bridges)
37
Describe the test for proteins
- add biuret reagent - positive test result (purple colour)
38
How do enzymes act as biological catalysts?
● Each enzyme lowers activation energy of reaction it catalyses ● To speed up rate of reaction
39
Describe the induced-fit model of enzyme actio
1. Substrate binds to (not completely complementary) active site of enzyme 2. Causing active site to change shape (slightly) so it is complementary to its substrate 3. So enzyme-substrate complex forms 4. Causing bonds in substrate to bend / distort, lowering activation energy Describe
40
Describe how models of enzyme action have changed over time
● Initially lock and key model (now outdated) ○ Active site a fixed shape, complementary to one substrate ● Now induced-fit model
41
Explain the specificity of enzymes
● Specific tertiary structure determines shape of active site ○ Dependent on sequence of amino acids (primary structure) ● Active site is complementary to a specific substrate ● Only this substrate can bind to active site, inducing fit and forming an enzyme-substrate complex
42
Describe and explain the effect of enzyme concentration on the rate of enzyme-controlled reaction
● As enzyme concentration increases, rate of reaction increases ○ Enzyme concentration = limiting factor (excess substrate) ○ More enzymes so more available active sites ○ So more enzyme-substrate complexes form ● At a certain point, rate of reaction stops increasing / levels off ○ Substrate concentration = limiting factor (all substrates in use)
43
Describe and explain the effect of substrate concentration on the rate of enzyme-controlled reactions
● As substrate concentration increases, rate of reaction increases ○ Substrate concentration = limiting factor (too few substrate molecules to occupy all active sites) ○ More enzyme-substrate complexes form ● At a certain point, rate of reaction stops increasing / levels off ○ Enzyme concentration = limiting factor ○ As all active sites saturated / occupied (at a given time
44
Describe and explain the effect of temperature on the rate of enzyme-controlled reactions
● As temperature increases to optimum, rate of reaction increases ○ More kinetic energy ○ So more enzyme-substrate complexes form ● As temperature exceeds optimum, rate of reaction decreases ○ Enzymes denature- tertiary structure and active site change shape ○ As hydrogen / ionic bonds break ○ So active site no longer complementary ○ So fewer enzyme-substrate complexes form
45
Describe and explain the effect of pH on the rate of enzyme-controlled reactions
● As pH increases / decreases above / below an optimum, rate of reaction decreases ○ Enzymes denature- tertiary structure and active site change shape ○ As hydrogen / ionic bonds break ○ So active site no longer complementary ○ So fewer enzyme-substrate complexes form 11
46
Describe and explain the effect of concentration of competitive inhibitors on the rate of enzyme-controlled reactions
● As concentration of competitive inhibitor increases, rate of reaction decreases ○ Similar shape to substrate ○ Competes for / binds to / blocks active site ○ So substrates can’t bind ○ So fewer enzyme-substrate complexes form ● Increasing substrate concentration reduces effect of inhibitors (dependent on relative concentrations of substrate and inhibitor)
47
Describe and explain the effect of concentration of non-competitive inhibitors on the rate of enzyme-controlled reactions
● As concentration of non-competitive inhibitor increases, rate of reaction decreases ○ Binds to site other than the active site (allosteric site) ○ Changes enzyme tertiary structure / active site shape ○ So active site no longer complementary to substrate ○ So substrates can’t bind ○ So substrates can’t bind ○ So fewer enzyme-substrate complexes form ● Increasing substrate concentration has no effect on rate of reaction as change to active site is permanent reaction
48
Describe the basic functions of DNA and RNA in all living cells DNA
DNA - Holds genetic information which codes for polypeptides (proteins) RNA - Transfers genetic information from DNA to ribosomes
49
Name the two types of molecule from which a ribosome is made
RNA and protein
50
RNA and dna nucleotide
DNA - Phosphate group, deoxyribose sugar, nitrogenous bases - adenine, thymine,guanine, cytosine RNA - phosphate group - ribose sugar, nitrogenous bases - adenine, uracil, guanine and cytosine
51
Describe how nucleotides join together to form polynucleotides
● Condensation reactions, removing water molecules ● Between phosphate group of one nucleotide and deoxyribose / ribose of another ● Forming phosphodiester bonds
52
Why did many scientists initially doubt that DNA carried the genetic code?
The relative simplicity of DNA - chemically simple molecule with few components
53
Describe the structure of DNA
● Polymer of nucleotides (polynucleotide) ● Each nucleotide formed from deoxyribose, a phosphate group and a nitrogen-containing organic base ● Phosphodiester bonds join adjacent nucleotides ● 2 polynucleotide chains held together by hydrogen bonds ● Between specific complementary base pairs- adenine / thymine and cytosine / guanine ● Double helix
54
Describe the structure of (messenger) RNA
● Polymer of nucleotides (polynucleotide) ● Each nucleotide formed from ribose, a phosphate group and a nitrogen-containing organic base ● Bases - uracil, adenine, cytosine, guanine ● Phosphodiester bonds join adjacent nucleotides ● Single helix
55
Compare and contrast the structure of DNA and (messenger) RNA Suggest
Pentose sugar is deoxyribose vs Pentose sugar is ribose Has the base thymine vs Has the base uracil Double stranded / double helix vs Single stranded / single helix Long (many nucleotides) vs Shorter (fewer nucleotides) Has hydrogen bonds / base pairing Does not
56
Suggest how the structure of DNA relates to its functions
● Two strands → both can act as templates for semi-conservative replication ● Hydrogen bonds between bases are weak → strands can be separated for replication ● Complementary base pairing → accurate replication ● Many hydrogen bonds between bases → stable / strong molecule ● Double helix with sugar phosphate backbone → protects bases / hydrogen bonds ● Long molecule → store lots of genetic information (that codes for polypeptides) ● Double helix (coiled)→ compac
57
Suggest how you can use incomplete information about the frequency of bases on DNA strands to find the frequency of other bases
1. % of adenine in strand 1 = % of thymine in strand 2 (and vice versa) 2. % of guanine in strand 1 = % of cytosine in strand 2 (and vice versa) Because of specific complementary base pairing between 2 strands
58
Why is semi-conservative replication important?
Ensures genetic continuity between generations of cells
59
Describe the process of semi-conservative DNA replication
1. DNA helicase breaks hydrogen bonds between complementary bases, unwinding the double helix 2. Both strands act as templates 3. Free DNA nucleotides attracted to exposed bases and join by specific complementary base pairing 4. Hydrogen bonds form between adenine-thymine and guanine-cytosine 5. DNA polymerase joins adjacent nucleotides on new strand by condensation reactions 6. Forming phosphodiester bonds Semi conservative- each new DNA molecule consists of one original / template strand and one new stran
60
semi conservative means
- each new DNA molecule consists of one original / template strand and one new strand
61
Use your knowledge of enzyme action to suggest why DNA polymerase moves in opposite directions along DNA strands
● DNA has antiparallel strands ● So shapes / arrangements of nucleotides on two ends are different ● DNA polymerase is an enzyme with a specific shaped active site ● So can only bind to substrate with complementary shape (phosphate end of developing strand)
62
Name the two scientists who proposed models of the chemical structure of DNA and of DNA replication
Watson and Crick
63
Describe the work of Meselson and Stahl in validating the Watson-Crick model of semi-conservative DNA replication
1. Bacteria grown in medium containing heavy nitrogen (15N) so nitrogen is incorporated into DNA bases ○ DNA extracted & centrifuged → settles near bottom, as all DNA molecules contain 2 ‘heavy’ strands 2. Bacteria transferred to medium containing light nitrogen (14N) and allowed to divide once ○ DNA extracted & centrifuged → settles in middle, as all DNA molecules contain 1 original ‘heavy’ and 1 new ‘light’ strand 3. Bacteria in light nitrogen (14N) allowed to divide again ○ DNA extracted & centrifuged → half settles in middle, as contains 1 original ‘heavy’ and 1 new ‘light’ strand; half settles near top, as contains 2 ‘light’ strands
64
ATP stands for
Adenosinetriphosphate
65
Describe the structure of ATP
● Ribose bound to a molecule of adenine (base) and 3 phosphate groups ● Nucleotide derivative (modified nucleotide)
66
Describe how ATP is broken down
● ATP (+ water)→ ADP (adenosine diphosphate) + Pi (inorganic phosphate) ● Hydrolysis reaction, using a water molecule ● Catalysed by ATP hydrolase (enzyme
67
Give two ways in which the hydrolysis of ATP is used in cells
● Coupled to energy requiring reactions within cells (releases energy) ○ eg. active transport, protein synthesis ● Inorganic phosphate released can be used to phosphorylate (add phosphate to) other compounds, making them more reactive
68
Describe how ATP is resynthesised in cells
● ADP + Pi → ATP (+ water) ● Condensation reaction, removing a water molecule ● Catalysed by ATP synthase (enzyme) ● During respiration and photosynthesis
69
Suggest how the properties of ATP make it a suitable immediate source of energy for cells
● Releases energy in (relatively) small amounts / little energy lost as heat ● Single reaction / one bond hydrolysed to release energy (so immediate release) ● Cannot pass out of cell
70
Explain how hydrogen bonds occur between water molecules
● Water is polar molecule ● Slightly negatively charged oxygen atoms attract slightly positively charged hydrogen atoms of other water molecules
71
5 properties of water
Metabolite Solvent High specific heat capacity Large latent heat of vaporisation Strong cohesion between water molecules
72
Water as a metabolite
Used in condensation / hydrolysis / photosynthesis / respiration
73
Water as a solvent
1. Allows metabolic reactions to occur (faster in solution) 2. Allows transport of substances eg. nitrates in xylem, urea in blood
74
High spc in water
● Buffers changes in temperature ● As can gain / lose a lot of heat / energy without changing temperature 1.Good habitat for aquatic organisms as temperature more stable than land 2. Helps organisms maintain a constant internal body temperature
75
Water as latent heat
● Allows effective cooling via evaporation of a small volume (eg. sweat) ● So helps organisms maintain a constant internal body temperature
76
Strong cohesion bet water mol
1. Supports columns of water in tube-like transport cells of plants eg. transpiration stream through xylem in plants 2. Produces surface tension where water meets air, supporting small organisms (to walk on water)
77
Where are inorganic ions found in the body?
In solution in cytoplasm and body fluid, some in high concentrations and others in very low concentrations
78
Role of hydrogen ions
● Maintain pH levels in the body → high concentration = acidic / low pH ● Affects enzyme rate of reaction as can cause enzymes to denature (topic 1.4.2)
79
Iron ions (Fe2+)
● Component of haem group of haemoglobin ● Allowing oxygen to bind / associate for transport as oxyhaemoglobin (topic 3.4.1)
80
Sodium ions (Na+)
1. Involved in co-transport of glucose / amino acids into cells (topic 2.3 / 3.3) 2. Involved in action potentials in neurons (topic 6.2) 3. Affects water potential of cells / osmosis (topic 2.3)
81
Phosphate ions (PO4 3-)
1. Component of nucleotides, allowing phosphodiester bonds to form in DNA / RNA 2. Component of ATP, allowing energy release 3. Phosphorylates other compounds making them more reactive (topic 1.6) 4. Hydrophilic part of phospholipids, allowing a bilayer to form (topic 1.3 / 2.3)

Bio Aqa (29 decks)

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