Topic 1: Biological Molecules Flashcards

Question

What are polysaccharides? Give three examples

Answer 1

Polymers made from many monosaccharides joined by glycosidic bonds formed by condensation reactions. When hydrolysed, they break down into disaccharides or monosaccharides. Starch, glycogen, cellulose

Answer 2

Add two drops of iodine solution to 2cm^3 of food sample. A positive result will turn from yellow to blue-black

Answer 3

Not found in animal cells. Usually stored as intracellular starch grains, especially in seeds.

Answer 4

Made from chains of alpha glucose monosaccharides. - Amylose chains = unbranched with 1-4 glycosidic bonds. Wound in a helix that makes the molecule compact. Hydroxyl groups pointing inwards form hydrogen bonds that hold the helix in place - Amylopectin chains = branched with 1-6 glycosidic bonds at side branches

Answer 5

- Insoluble = doesn't affect water potential so water not drawn in by osmosis - Large + insoluble = doesn't diffuse out cells - Compact = a lot stored in a small space - Forms alpha glucose when hydrolysed = easily transported + readily used in respiration - Branches = many ends = acted on by enzymes simultaneously = glucose released rapidly

Answer 6

Animals and bacteria (never plants), stored in small granules in muscles and the liver (although fat is the main storage molecule in animals)

Answer 7

Similar to starch but more highly branched with shorter chains - Made from chains of alpha glucose with 1-4 and 1-6 (at side branches) glycosidic bonds

Answer 8

- Insoluble = doesn't draw water into cells by osmosis - Insoluble = doesn't diffuse out cells - Compact = lots stored in a small space (good for mobile animals) - More highly branched = more ends acted on by enzymes simultaneously = more rapidly broken down into glucose for respiration ( animals have higher metabolic + respiratory rate than plants because more active)

Answer 9

In plant cell walls as a rigid structural molecule

Answer 10

Monomers of beta glucose form straight, unbranched chains. Hydrogen bonds between adjacent parallel chains strengthen substance. Adjacent beta-glucose molecules rotate 180 degrees so hydroxyl groups can form hydrogen bonds. Grouped into microfibrils which are arranged into parallel fibrils.

Answer 11

- Provides rigidity to plant cells - Stops cells bursting as water enters by osmosis by exerting an inward pressure, stopping further influx of water - Makes plant cells turgid + push against each other, making non-woody parts of the plant semi-rigid

Answer 12

- Made from beta-glucose molecules = form long, straight unbranched chains - Molecular chains run parallel + are cross-linked by hydrogen bonds, adding collective strength - Molecules grouped into microfibrils, which are grouped into fibres, adding more strength - Microfibrils permeable to water as cells need it for metabolic reactions

Answer 13

Carbon, hydrogen, oxygen Proportion of O to C and H is smaller than carbohydrates Insoluble to water but soluble in organic solvent solvents (e.g alchohols, acetone)

Answer 14

- Cell membranes - phospholipids contribute to flexibility + transfer of lipid-soluble substances - Energy source - provide over 2x energy as the same mass of carbohydrate, and provide water - Waterproofing - insoluble in water so form waxy, lipid cuticles to conserve water OR an oily secretion (sebum) in mammals - Insulation - slow conductors so stored beneath surface to retain body heat + around nerve cells (electrical insulators) - Protection - often stored around delicate organs

Answer 15

Fats are solid at room temperature, oils are liquid

Answer 16

- Put 2cm^3 of food sample and 5cm^3 of ethanol in a completely dry test tube - Shake thoroughly to dissolve lipid - Add 5cm^3 of water and shake gently - Positive result = milky white emulsion (because lipid droplets dispersed finely) - As a control, repeat with just water, should remain clear

Answer 17

3 fatty acids form ester bonds with glycerol in a condensation reaction (hydrolysis = inverse) Differences in properties come from variations in the fatty acids: All have a carboxyl group + a hydrocarbon chain

Answer 18

Can be saturated (C atoms linked to the maximum possible number of H), mono-unsaturated (one C=C) or poly-unsaturated (many C=C) Double bonds cause the molecule to bend = can't pack together closely = liquid at room temp

Answer 19

- High ratio of energy-storing C-H bonds to C atoms = excellent source of energy - Low mass : energy ratio = lots of energy in a small volume = good storage molecule for mobile animals (less mass) - Large + non-polar = insoluble in water = doesn't affect osmosis or water potential of cells - High ratio of H:C atoms = release water when oxidised = source of water

Answer 20

Triglycerides Phospholipids

Answer 21

One glycerol, two fatty acids and a phosphate molecule form ester bonds in a condensation reaction. They are polar molecules (two ends behave differently). They have a polar head (phosphate molecules are hydrophilic - attract water and don't mix with fat) and a non-polar tail (fatty acids are hydrophobic - repel water and mix with fat)

Answer 22

Because they are polar molecules, they position themselves so the hydrophilic heads are as close to water as possible, with the hydrophobic tails as far away as possible

Answer 23

- Polar molecules = in aqueous environments, phospholipids form a bilayer within cell-surface membranes = a hydrophobic barrier is formed between the inside/outside of a cell - Hydrophilic phosphate heads help to hold at the surface of the cell-surface membrane - Phospholipid structure lets them form glycolipids by combining with carbohydrates within the cell-surface membrane. Important in cell recognition

Answer 24

Usually very large molecules but there are many types. Amino acids are the monomer units that combine to make a polymer called a polypeptide. These can combine to make proteins.

Answer 25

20 Individual amino acids have a tetrahedral shape due to the angles of the bonds

Answer 26

Two amino acids joined by a peptide bond (between N and C) by a condensation reaction.

Answer 27

H R O \ | // N - C - C / | \ H H O-H NH2 = amino group R = variable group COOH = carboxyl group The OH from the carboxyl group and a H from the amino group of another acid

Answer 28

H R1 H R2 O \ | | | // N - C - C -- N - C - C / | || | \ H H O H O-H C=O = carbonyl group peptide bond = C--N

Answer 29

- Add equal volumes of the food sample and Biuret's reagent - Positive result = turns from blue to purple

Answer 30

- Many amino acids join by a series of condensation reactions to form polypeptides (polymerisation). - Primary structure is the sequence of amino acids (determined by DNA) - Primary structure determines its shape (specific to function) - A change in 1 amino acid can change the shape (+ function)

Answer 31

Hydrogen bonding (between the electronegative oxygen of carbonyl groups and the slightly positive hydrogen of NH groups) of the peptide backbone folds amino acids into a repeating structure Can be an alpha-helix or beta-pleated sheet

Answer 32

- Secondary protein structure is twisted and folded further into a 3D pattern due to side chain interactions. - Maintained by disulfide bridges, ionic bonds and hydrogen bonds - 3D shape is important to function (so the protein is distinctive + recognisable to other molecules) - All globular proteins display tertiary structure

Answer 33

- Disulfide bridges - strong + not easily broken - Ionic bonds - between the carboxyl + amino groups not involved in peptide bonds, easily broken by pH changes - Hydrogen bonds - numerous but easily broken

Answer 34

Large proteins made from multiple polypeptide chains ( and non-protein / prosthetic groups) combined and held together by bonds. While 3D structure is important to function, primary structure determines the shape in the first place

Answer 35

A protein with a roughly spherical shape, mostly used for metabolic functions

Answer 36

A protein made from long chains, mostly used for structural functions Collagen

Answer 37

Globular protein that is reaction specific and acts as a biological catalyst (alters the rate of reaction without undergoing permanent change). Can be used repeatedly so are effective in small amounts

Answer 38

-Reactants collide with enough energy to alter the arrangement of atoms - Free energy of the products must be less than the substrates - Must have the activation energy

Answer 39

- Energy of a system available to perform work - Minimum amount of energy needed to start a reaction

Answer 40

- Lower the activation energy of a reaction so it can occur at a lower temperature - Allows metabolic reactions to occur at body temp which would otherwise be too slow to sustain life

Answer 41

- Enzymes bring substrate molecules together - Enzyme's active site affects bonds in the substrate so they are easier to break

Answer 42

Globular proteins at the tertiary structure, have a specific 3D shape which is a result of their sequence of amino acids (primary structure) Have an active site - functional region of the enzyme that the substrate binds to, made from a relatively small number of amino acids. Forms a small depression in the large molecule

Answer 43

Active site has a shape complementary to the substrate (molecule that the enzyme acts on). Certain amino acids in the active site temporarily bond to the substrate, forming an enzyme-substrate complex

Answer 44

Lock and Key and Induced Fit Induced Fit

Answer 45

- Substrate and enzyme shapes fit exactly, enzyme is considered a rigid structure - Suggests enzymes are rigid when they are flexible (molecules can bind to sites other than the active site which alters its shape)

Answer 46

- Proximity of the substrate changes the shape of the active site to mould around it - As it changes shape, it puts strain on the substrate's bonds, reducing the activation energy needed to break it. Any change in the enzyme's environment can change its shape - Enzyme-substrate complex forms and substrate is converted into products - When product leaves enzyme, active site returns to original shape - Shows how enzyme activity can be altered by other molecules (e.g inhibitors) - Shows how activation energy is lowered

Answer 47

- Must have an active site complementary to the substrate - Must come into physical contact with the substrate

Answer 48

- Rate of formation of product (upward curve on graph before it levels off) - Rate of disappearance of substrate (downwards curve on graph before it levels off)

Answer 49

- At first, lots of substrate but no product - Collisions between substrate + enzyme molecules frequent - All active sites occupied at once = substrate broken down rapidly - As reaction continues less substrate and more product - More difficult for contact between substrate + enzyme as there is less substrate + product molecules get in the way = slower rate - Rate continues to slow until so little substrate present that concentration can't be measured - Reaction stops when all the substrate is used up

Answer 50

- Temperature - pH - Enzyme concentration - Substrate concentration - Presence of inhibitors

Answer 51

- As temp increases, so does kinetic energy = molecules move quicker = more frequent collisions with more force. More enzyme-substrate complexes = quicker rate. - Optimum temp for that enzyme = fastest rate - After optimum temp, temp increases make atoms vibrate, breaking hydrogen, ionic + disulphide bonds in the enzyme, changing its shape. Substrate doesn't fit as well = lower rate - Denatured - at extreme temps, enzyme changes shape so much it no longer works (permanent change)

Answer 52

- Despite a higher metabolic rate, too much additional food would be needed to maintain 40 - Other proteins may be denatured at higher temperatures - Any further increase in temperature (e.g illness) could denature the enzymes

Answer 53

All enzymes have an optimum pH, any changes reduce its rate, extreme changes denature the enzyme because: - Change in H+ ion concentration alters charges on amino acids in the active site, so substrate can no longer bind + enzyme-substrate complex can't be formed - Significant changes could break hydrogen + ionic bonds maintaining the tertiary structure, changing the shape of the active site

Answer 54

- Low enzyme conc + rate- substrate in excess = not all substrates in an active site. Increase in enzyme concentration = proportional increase in rate (more active sites available) - Max rate - all substrate molecules occupy an active site at once - Very high enzyme conc - enzyme conc exceeds substrate (substrate is limiting factor) so further increase of enzymes has no effect as all substrate molecules already fill an active site

Answer 55

- Low substrate conc + rate - too few substrate molecules to occupy all active sites. As substrate concentration increases, rate increases proportionally - Max rate (Vmax) - all active sites occupied by substrate - When substrate is in excess, further increase in substrate has no effect as all active sites are full

Answer 56

A substance that directly or indirectly alters the active site of an enzyme, reducing its activity

Answer 57

- Permanent inhibitors - inhibitor binds so strongly to the enzyme that it can never be removed - Reversible inhibitors - most inhibitors only bind temporarily

Answer 58

- Competitive inhibitors - Non-competitive inhibitors

Answer 59

- Have a molecular shape similar to the substrate so can occupy the active site - Compete with substrate for available active sites - The difference in concentrations of inhibitor and substrate determines its effect (determines the likelihood of the next molecule to bind to the active site being a substrate molecule) - Eventually all substrate molecules will occupy an active site. Time taken depends on inhibitor concentration

Answer 60

- Bind to the enzyme at a site other than the active site (so don't need to resemble its shape) - Alter the shape of the active site so it is no longer complementary to the substrate and no enzyme-substrate complexes can form - Increasing substrate concentration has no effect as they aren't competing for the same site

Answer 61

A chemical that needs to be kept at a constant concentration often inhibits an enzyme at the start of the reaction that produces it If its concentration increases, more of it is available to inhibit the enzyme, producing less of it and decreasing its concentration.

Answer 62

Polynucleotides (polymers made from nucleotide monomers). DNA and RNA are important information-carrying molecules

Answer 63

- A pentose sugar (5 carbon atoms) - Phosphate group - Nitrogenous organic base (Adenine, Guanine, Cytosine, Thymine, Uracil) The base and the phosphate group both attach to the pentose sugar

Answer 64

Condensation reactions between the phosphate group of one nucleotide and the pentose sugar of another forms a phosphodiester bond. Forms dinucleotides and polynucleotides

Answer 65

Ribonucleic acid A single, relatively short polynucleotide chain The pentose sugar is ribose and the organic bases are adenine, guanine, cytosine and uracil

Answer 66

- One type transfers genetic information from DNA to the ribosomes - Ribosomes are made from proteins and another type of RNA - A third type of RNA is involved in protein synthesis

Answer 67

Deoxyribonucleic acid The pentose sugar is deoxyribose The organic bases are guanine, cytosine, adenine and thymine

Answer 68

Made from two very long polynucleotide strands joined by hydrogen bonds between complementary base pairs Strands are antiparallel (run in different directions) and arranged in a double helix Strands have a structural phosphate-deoxyribose backbone

Answer 69

Always specific - A with T (U in RNA) and G with C The base pairs are complementary SO quantities of A and T (and G and C) are equal. Ratio between two pairs varies between species 3 hydrogen bonds form between G and C but only 2 between A and T

Answer 70

Very stable molecule - Phosphodiester backbone protects more chemically reactive organic bases inside the double helix - Base stacking (other interactive forces between base pairs) hold the molecule together - Stability varies within molecule as G-C pairings have 3 H-bonds but A-T has 2. Higher proportion of G-C means a more stable molecule

Answer 71

- The hereditary material responsible for passing genetic information between cells and generations - Billions of base pairs in the DNA of a typical mammal = almost infinite variety of sequences = genetic diversity

Answer 72

- DNA coils around histones (proteins) to form chromosomes - Chromosomes found in the nucleus of the cell - Humans usually have 46 chromosomes (23 pairs)

Answer 73

- Very stable = passes from generation to generation without significant change (mutations are repaired so are rare) - Strands only joined by hydrogen bonds = allows them to separate in DNA replication + protein synthesis - Very large molecule = carries huge amount of genetic information - Base pairs within helical cylinder of deoxyribose-phosphate backbone = genetic information protected from corruption by outside chemical/physical forces - Base pairing = DNA can replicate + transfer information as mRNA

Answer 74

Thought it was proteins due to their chemical diversity. Thought DNA had too few components with a too simple structure

Answer 75

- Injected mouse with living safe bacterium that doesn't cause pneumonia + dead harmful form that does - mouse developed pneumonia - Only explanation was that dead bacterium had information on how to make the toxin but not the means, and the safe form had means but not info - Substances from dead bacteria were isolated and added to the safe form. Only the DNA let it produce the toxin, so must be hereditary material - When enzymes that break down DNA were added, it stopped producing the toxin

Answer 76

Apart from zygotes, all cells in multicellular organisms made from existing cells by cell division. First nuclear division (mitosis/meiosis) then cytokinesis (whole cell divides) Must replicate before nuclear division so all new cells have all genetic information to produce the proteins they need

Answer 77

Semi-conservative replication - A pool of the 4 nucleotides present (free nucleotides) - Both strands of DNA being copied as a template - The enzymes DNA helicase and DNA polymerase are present - A source of chemical energy (ATP) to drive the process

Answer 78

DNA helix unwinds so each new DNA molecule contains one original polynucleotide strand used as a template and one new strand. Contains half original DNA and half new

Answer 79

1) Enzyme DNA helicase breaks H bonds between nitrogenous bases, separates double helix + unwinds into 2 strands 2) Hydrolysis of ATP activates free nucleotides in nucleus 3) Each exposed polynucleotide strand acts as a template to which complementary free nucleotides attach 4) Nucleotides joined in condensation reactions by enzyme DNA polymerase to form new polynucleotide strand 5) 'Proof-reading' enzyme checks for mutations + a 'winding' enzyme winds polynucleotides into 2 DNA double helices 6) 2 daughter DNA molecules are genetically identical + contain half original, half new DNA

Answer 80

DNA strands are antiparallel - one is 3' to 5' (based on carbon numbers in deoxyribose) other is 5' to 3'. Active site of DNA polymerase only complementary to 3' end so nucleotides can only be added to the 3' end New strand is made in a 5' to 3' direction so DNA polymerase enzymes on each strand work in opposite directions

Answer 81

Watson and Crick with the help of Rosalind Franklin Proposed the semi-conservative model - Conservative model = original molecule stays intact + a separate daughter molecule built from scratch - Dispersive model = new molecule is half new, half original but original/new nucleotides are scattered throughout molecule (no strand stays intact)

Answer 82

Meselson and Stahl 1) Grew bacteria (because they replicate quickly) in a growth medium with the heavy isotope of nitrogen (15N) until all their DNA had incorporated 15N 2) Centrifuged bacteria to isolate DNA and 100% formed a band lower in the tube (more dense area) 3) Grew bacteria in 14N (light isotope) for 1 generation. After centrifugation, 100% DNA is hybrid (middle band). Disproved conservative model (would have 50% heavy, 50% light) 4) After 2nd generation, 50% formed a band at 14N and 50% was hybrid. Disproved dispersive (would have 100% hybrid) So semi-conservative is the only valid model

Answer 83

Adenosine Triphosphate A phosphorylated macromolecule made from adenine (nitrogenous base), a ribose sugar and 3 phosphate groups The adenine and the three phosphate groups attach to the ribose with high energy bonds (are unstable = low activation energy = easily broken)

Answer 84

A short-term (immediate) energy source - holds a convenient amount of energy to do work in the cell which is released when it is broken down

Answer 85

- Releases less energy = more manageable + less is wasted as heat - Hydrolysis of ATP is a single reaction = very quick release, breakdown of glucose requires several reactions = slower

Answer 86

An exergonic reaction catalysed by the ATP hydrolase enzyme to release energy. It is reversible ATP + H20 -> ADP + Pi + E ADP = adenosine diphosphate Pi = inorganic phosphate E = energy

Answer 87

An endergonic condensation reaction (phosphorylation) catalysed by the enzyme ATP synthase. Uses energy supplied by respiration ADP + Pi -> ATP + H20 ADP = adenosine diphosphate Pi = inorganic phosphate

Answer 88

- Photophosphorylation - in chlorophyll-containing plant cells during photosynthesis - Oxidative phosphorylation - in the mitochondria of plant + animal cells during respiration - Substrate-level phosphorylation - in plant + animal cells when phosphate groups are transferred from donor molecules to ADP

Answer 89

- Metabolic processes e.g building of macromolecules - Movement - energy for muscle filaments to slide past each other, shortening the muscle fibre, contracting the muscle - Active transport - change shape of carrier proteins in plasma membranes so molecules can move against concentration gradient - Secretion - form lysosomes necessary for secretion of cell products - Activation of molecules - inorganic phosphate released during ATP hydrolysis can phosphorylate other compounds to make them more reactive + lower activation energy

Answer 90

Something that allows work to be done. Can be changed between forms (e.g magnetic, light, heat) but never created or destroyed. Most energy used by organisms is stored in chemical bonds in molecules.

Answer 91

An atom/group of atoms that have an electric charge by losing/gaining electrons. Not based on carbon Found in cell cytoplasm + body fluids in high or low concentrations

Answer 92

- Irons ions - found in haemoglobin to play a role in oxygen transport - Phosphate ions - structural role in DNA + storing energy in ATP - Hydrogen ions - determine pH of solutions + so function of enzymes - Sodium ions - important in transport of glucose + amino acids across plasma membranes

Answer 93

Two hydrogen atoms covalently bonded to an oxygen atom. O has a slight negative charge and H is slightly positive making it a dipolar molecule. Positive pole of one molecule attracted to the negative pole of another, forming a hydrogen bond

Answer 94

- High specific heat capacity - High latent heat of vaporisation - Cohesion - Adhesion - Surface tension - Good solvent - Metabolite - Not easily compressed - Transparent

Answer 95

- Hydrogen bonds = high SHC because energy is used to break bonds before molecules can move faster. Doesn't change temp easily = acts as a buffer against sudden temp changes. = Thermostable aquatic environments (habitats), minimises temp fluctuations inside cells (constant optimum conditions for enzymes for metabolism) - Hydrogen bonds = high LHV (takes a lot of energy to evaporate) = used as a cooling mechanism (body heat used to evaporate sweat)

Answer 96

- Cohesion = water molecules stick together (form H bonds). Adhesion = water molecules stick to something else (H bonds). Together they allow water to be pulled up xylem vessels for one-way transport in plants - Surface tension = measure of how difficult it is to break surface of a liquid = allows some organisms to walk on water - Solvent - readily dissolves substances because dipolar molecules can surround ions (due to charge attraction) + prevent ionic bonds from forming, breaking up the substance

Answer 97

- Metabolite - used in hydrolysis, made by condensation, raw material in photosynthesis, chemical reactions take place in aqueous mediums - Not easily compressed = support (e.g turgor pressure in herbaceous plants, hydrostatic skeletons of animals) - Transparent = light can get to aquatic plants for photosynthesis, light-rays can penetrate jelly-like fluid that fills the eye + reach the retina

Topic 1: Biological Molecules Flashcards

(121 cards)