Biological molecules Flashcards

Question

what is the structure of saturated fatty acids?

Answer 1

Saturated fatty acids don’t have any double bonds between their carbon atoms. The fatty acid is ‘saturated’ with hydrogen.

Answer 2

Unsaturated fatty acids have at least one double bond | between carbon atoms, which cause the chain to kink.

Answer 3

1) Phospholipids are also macromolecules. They’re pretty similar to triglycerides except one of the fatty acid molecules is replaced by a phosphate group. 2) The phosphate group is hydrophilic (it attracts water molecules) and the fatty acid tails are hydrophobic.

Answer 4

In animals and plants, triglycerides are mainly used as energy storage molecules. Some bacteria (e.g. Mycobacterium tuberculosis) use triglycerides to store both energy and carbon. Triglycerides are good for storage because: 1) The long hydrocarbon tails of the fatty acids contain lots of chemical energy — a load of energy is released when they’re broken down. Because of these tails, lipids contain about twice as much energy per gram as carbohydrates. 2) They’re insoluble, so they don’t cause water to enter the cells by osmosis (see p. 58) which would make them swell. The triglycerides bundle together as insoluble droplets in cells because the fatty acid tails are hydrophobic (water-repelling) — the tails face inwards, shielding themselves from water with their glycerol heads.

Answer 5

Phospholipids are found in the cell membranes of all eukaryotes and prokaryotes. They make up what’s known as the phospholipid bilayer (see p. 50). Cell membranes control what enters and leaves a cell. 1) Phospholipid heads are hydrophilic and their tails are hydrophobic, so they form a double layer with their heads facing out towards the water on either side. 2) The centre of the bilayer is hydrophobic, so water-soluble substances can’t easily pass through it — the membrane acts as a barrier to those substances.

Answer 6

Cholesterol is another type of lipid — it has a hydrocarbon ring structure attached to a hydrocarbon tail. The ring structure has a polar hydroxyl (OH) group attached to it. In eukaryotic cells, cholesterol molecules help to regulate the fluidity of the cell membrane by interacting with the phospholipid bilayer. 1) Cholesterol has a small size and flattened shape — this allows cholesterol to fit in between the phospholipid molecules in the membrane. 2) At higher temperatures, they bind to the hydrophobic tails of the phospholipids, causing them to pack more closely together. This helps to make the membrane less fluid and more rigid. 3) At lower temperatures, cholesterol prevents phospholipids from packing too close together, and so increases membrane fluidity.

Answer 7

Long chains of amino acid

Answer 8

When two amino acids join together

Answer 9

When more than two amino acids joined together

Answer 10

one or more polypeptides

Answer 11

All amino acids have the same general structure — a carboxyl group (-COOH) and an amino group (-NH ) attached to a carbon atom. The difference between different 2 amino acids is the variable group (R on diagram) they contain. 2) All amino acids contain the chemical elements carbon, oxygen, hydrogen and nitrogen. Some also contain sulfur.

Answer 12

peptide bonds to form dipeptides on polypeptides

Answer 13

when a molecule of water is released during the reaction

Answer 14

When a reaction adds a molecule of water to break the peptide bond

Answer 15

Primary secondary tertiary and quaternary

Answer 16

Primary Structure — this is the sequence of amino acids in the polypeptide chain. Different proteins have different sequences of amino acids in their primary structure. A change in just one amino acid may change the structure of the whole protein.

Answer 17

Secondary Structure — the polypeptide chain doesn’t remain flat and straight. Hydrogen bonds form between nearby amino acids in the a chain. This makes it automatically coil into an alpha ( ) helix or fold b into a beta ( ) pleated sheet — this is the secondary structure.

Answer 18

Tertiary Structure — the coiled or folded chain of amino acids is often coiled and folded further. More bonds form between different parts of the polypeptide chain. For proteins made from a single polypeptide chain, the tertiary structure forms their final 3D structure.

Answer 19

Quaternary Structure — some proteins are made of several different polypeptide chains held together by bonds. The quaternary structure is the way these polypeptide chains are assembled together. E.g. haemoglobin is made of four polypeptide chains, bonded together. For proteins made from more than one polypeptide chain, the quaternary structure is the protein’s final 3D structure.

Answer 20

peptide between the amino acids

Answer 21

Hydrogen bonds

Answer 22

ionic bond disulfide bonds hydrophobic and hydrophilic interactions hydrogen bonds

Answer 23

Ionic bonds. These are attractions between negatively-charged R groups and positively-charged R groups on different parts of the molecule.

Answer 24

Disulfide bonds. Whenever two molecules of the amino acid cysteine come close together, the sulfur atom in one cysteine bonds to the sulfur in the other cysteine, forming a disulfide bond.

Answer 25

Hydrophobic and hydrophilic interactions. When hydrophobic (water-repelling) R groups are close together in the protein, they tend to clump together. This means that hydrophilic (water‑attracting) R groups are more likely to be pushed to the outside, which affects how the protein folds up into its final structure.

Answer 26

Hydrogen bonds — these weak bonds form between slightly positively-charged hydrogen atoms in some R groups and slightly negatively-charged atoms in other R groups on the polypeptide chain.

Answer 27

Quaternary structure — this tends to be determined by the tertiary structure of the individual polypeptide chains being bonded together. Because of this, it can be influenced by all the bonds mentioned above.

Answer 28

Globular Proteins Are Round and Compact 1) In a globular protein, the hydrophilic R groups on the amino acids tend to be pushed to the outside of the molecule. This is caused by the hydrophobic and hydrophilic interactions in the protein’s tertiary structure (see previous page). 2) This makes globular proteins soluble, so they’re easily transported in fluids. 3) Globular proteins have a range of functions in living organisms.

Answer 29

HAEMOGLOBIN is a globular protein that carries oxygen around the body in red blood cells (see page 86). It’s known as a conjugated protein — this means it’s a protein with a non-protein group attached. The non-protein part is called a prosthetic group. Each of the four polypeptide chains in haemoglobin has a prosthetic group called haem. A haem group contains iron, which oxygen binds to.

Answer 30

INSULIN is a hormone secreted by the pancreas. It helps to regulate the blood glucose level. Its solubility is important — it means it can be transported in the blood to the tissues where it acts. An insulin molecule consists of two polypeptide chains, which are held together by disulfide bonds.

Answer 31

AMYLASE is an enzyme (see page 42) that catalyses the breakdown of starch in the digestive system. It is made of a single chain of amino acids. Its secondary structure contains both alpha-helix and beta-pleated sheet sections. Most enzymes are globular proteins.

Answer 32

Fibrous proteins are insoluble and strong. They’re structural proteins and are fairly unreactive

Answer 33

Collagen keratin elastin

Answer 34

Collagen — found in animal connective tissues, such as bone, skin and muscle. It is a very strong molecule. Minerals can bind to the protein to increase its rigidity, e.g. in bone.

Answer 35

Keratin — found in many of the external structures of animals, such as skin, hair, nails, feathers and horns. It can either be flexible (as it is in skin) or hard and tough (as it is in nails).

Answer 36

• Elastin — found in elastic connective tissue, such as skin, large blood vessels and some ligaments. It is elastic, so it allows tissues to return to their original shape after they have been stretched.

Answer 37

Ca2+ Involved in the transmission of nerve impulses and the release of insulin from the pancreas. Acts as a cofactor for many enzymes e.g. those involved in blood clotting. Is important for bone formation.

Answer 38

Na+ Important for generating nerve impulses, for muscle contraction and for regulating fluid balance in the body.

Answer 39

k+ important for generating nerve impulses, for muscle contraction and for regulating fluid balance in the body. Activates essential enzymes needed for photosynthesis in plant cells

Answer 40

h+ Affects the pH of substances (more H+ ions than OH– ions in a solution creates an acid). Also important for photosynthesis reactions that occur in the thylakoid membranes inside chloroplasts

Answer 41

NH4+ Absorbed from the soil by plants and is an important source of nitrogen + (which is then used to make, e.g. amino acids, nucleic acids).

Answer 42

NO3- Absorbed from the soil by plants and is an important source of nitrogen – (which is then used to make, e.g. amino acids, nucleic acids).

Answer 43

HCO3- | Acts as a buffer, which helps to maintain the pH of the blood

Answer 44

Cl- Involved in the ‘chloride shift’ which helps to maintain the pH of the blood during gas exchange (see p. 87). Acts as a cofactor for the enzyme amylase (see p. 47). Also involved in some nerve impulses.

Answer 45

PO4 3- Involved in photosynthesis and respiration reactions. Needed for the synthesis of many biological molecules, such as nucleotides (including 3– ATP), phospholipids, and calcium phosphate (which strengthens bones).

Answer 46

OH- Affects the pH of substances (more OH– ions than H+ ions in a solution creates an alkali).

Answer 47

ion with positive charge

Answer 48

ion with negative charge

Answer 49

monnosacharides and disacharides?

Answer 50

reducing non-reducing

Answer 51

Benedict's test

Answer 52

1) Reducing sugars include all monosaccharides (e.g. glucose) and some disaccharides (e.g. maltose and lactose). 2) You add Benedict’s reagent (which is blue) to a sample and heat it in a water bath that’s been brought to the boil. The colour of the precipitate blue green yellow orange brick red changes from: 3) If the test’s positive it will form a coloured precipitate (solid particles suspended in the solution). 4) The higher the concentration of reducing sugar, the further the colour change goes — you can use this to compare the amount of reducing sugar in different solutions. A more accurate way of doing this is to filter the solution and weigh the precipitate.

Answer 53

1) If the result of the reducing sugars test is negative, there could still be a non-reducing sugar present. To test for non-reducing sugars, like sucrose, first you have to break them down into monosaccharides. 2) You do this by getting a new sample of the test solution, adding dilute hydrochloric acid and carefully heating it in a water bath that’s been brought to the boil. You then neutralise it with sodium hydrogencarbonate. Then just carry out the Benedict’s test as you would for a reducing sugar. 3) If the test’s positive it will form a coloured precipitate (as for the reducing sugars test). If the test’s negative the solution will stay blue, which means it doesn’t contain any sugar (either reducing or non-reducing).

Answer 54

Use Test Strips for Glucose Glucose can also be tested for using test strips coated in a reagent. The strips are dipped in a test solution and change colour if glucose is present. The colour change can be compared to a chart to give an indication of the concentration of glucose present. The strips are useful for testing a person’s urine for glucose, which may indicate they have diabetes.

Answer 55

Use the Iodine Test for Starch Just add iodine dissolved in potassium iodide solution to the test sample. • If starch is present, the sample changes from browny-orange to a dark, blue-black colour. • If there’s no starch, it stays browny-orange.

Answer 56

Use the Biuret Test for Proteins There are two stages to this test. 1) The test solution needs to be alkaline, so first you add a few drops of sodium hydroxide solution. 2) Then you add some copper(II) sulfate solution. • If protein is present the solution turns purple. • If there’s no protein, the solution will stay blue.

Answer 57

Use the Emulsion Test for Lipids Shake the test substance with ethanol for about a minute, then pour the solution into water. • If lipid is present, the solution will turn milky. • The more lipid there is, the more noticeable the milky colour will be. • If there’s no lipid, the solution will stay clear.

Answer 58

Used to Determine the Concentration of a Glucose Solution

Answer 59

1) You can use Benedict’s reagent and a colorimeter to get a quantitative estimate of how much glucose (or other reducing sugar) there is in a solution. 2) A colorimeter is a device that measures the strength of a coloured solution by seeing how much light passes through it 3) A colorimeter measures absorbance (the amount of light absorbed by the solution). The more concentrated the colour of the solution, the higher the absorbance is 4) It’s easiest to measure the concentration of the blue Benedict’s solution that’s left after the test (the paler the solution, the more glucose there was). So, the higher the glucose concentration, the lower the absorbance of the solution.

Answer 60

Initially you need to make up several glucose solutions of different, known concentrations. You can do this using a serial dilution technique: This is how you’d make five serial dilutions with a dilution factor of 2, starting with an initial glucose concentration of 40 mM... 1) Line up five test tubes in a rack. 2) Add 10 cm3 of the initial 40 mM glucose solution to the first test tube and 5 cm3 of distilled water to the other four test tubes. 3) Then, using a pipette, draw 5 cm3 of the solution from the first test tube, add it to the distilled water in the second test tube and mix the solution thoroughly. You now have 10 cm3 of solution that’s half as concentrated as the solution in the first test tube (it’s 20 mM). 4) Repeat this process three more times to create solutions of 10 mM, 5 mM and 2.5 mM.

Answer 61

Once you’ve got your glucose solutions, you need to make a calibration curve. Here’s how: 1) Do a Benedict’s test on each solution (plus a negative control of pure water). Use the same amount of Benedict’s solution in each case. 2) Remove any precipitate — either leave for 24 hours (so that the precipitate settles out) or centrifuge them. 3) Use a colorimeter (with a red filter) to measure the absorbance 1.0 of the Benedict’s solution remaining in each tube. 4) Use the results to make the calibration curve, showing absorbance against glucose concentration. Then you can test the unknown solution in the same way as the known concentrations and use the calibration curve to find its concentration.

Answer 62

Biosensors Can Detect Chemicals in a Solution 1) A biosensor is a device that uses a biological molecule, such as an enzyme (see page 42) to detect a chemical. 2) The biological molecule produces a signal (e.g. a chemical signal), which is converted to an electrical signal by a transducer (another part of the biosensor). 3) The electrical signal is then processed and can be used to work out other information. Example: Glucose Biosensors 1) A glucose biosensor is used to determine the concentration of glucose in a solution. 2) It does this using the enzyme glucose oxidase and electrodes. 3) The enzyme catalyses the oxidation of glucose at the electrodes — this creates a charge, which is converted into an electrical signal by the electrodes (the transducer). 4) The electrical signal is then processed to work out the initial glucose concentration.

Answer 63

Chromatography is Good for Separating and Identifying Things 1) Chromatography is used to separate stuff in a mixture — once it’s separated out, you can often identify the components. 2) For example, chromatography can be used to separate out and identify biological molecules such as amino acids, carbohydrates, vitamins and nucleic acids. 3) There are quite a few different types of chromatography — you only need to know about paper chromatography and thin-layer chromatography.

Answer 64

1) A MOBILE PHASE — where the molecules can move. • In both paper and thin-layer chromatography the mobile phase is a liquid solvent, such as ethanol or water. 2) A STATIONARY PHASE — where the molecules can’t move. • In paper chromatography the stationary phase is a piece of chromatography paper. • In thin-layer chromatography the stationary phase is a thin (0.1-0.3 mm) layer of solid, e.g. silica gel, on a glass or plastic plate.

Answer 65

Paper Chromatography is used to Identify Unknown Amino Acids

Answer 66

1) Draw a pencil line near the bottom of a piece of chromatography paper and put a concentrated spot of the mixture of amino acids on it. It’s best to carefully roll the paper into a cylinder with the spot on the outside so it’ll stand up. 2) Add a small amount of prepared solvent (a mixture of butan-1-ol, glacial ethanoic acid and water is usually used for amino acids) to a beaker and dip the bottom of the paper into it (not the spot). This should be done in a fume cupboard. Cover with a lid to stop the solvent evaporating.3) As the solvent spreads up the paper, the different amino acids (solutes) move with it, but at different rates, so they separate out. 4) When the solvent’s nearly reached the top, take the paper out and mark the solvent front with pencil. Then you can leave the paper to dry out before you analyse it (see below). 5) Amino acids aren’t coloured, which means you won’t be able to see them on the paper. So before you can analyse them, you have to spray the paper with ninhydrin solution to turn the amino acids purple. This should also be done in a fume cupboard and gloves should be worn. (Note: you can’t use ninhydrin to detect all biological molecules, only proteins and amino acids.) 6) You can then use R values to identify the separated molecules:

Answer 67

An R value is the ratio of the distance travelled by a solute to the distance travelled by the solvent. You can calculate it using this formula: R value of amino acid = distance travelled by solute / distance travelled by solvent When you’re measuring how far a solute has travelled, you measure from the point of origin to the vertical centre of the spot. You can work out what was in a mixture by calculating an R value for each solute and looking each R value up in a database, or table, of known values.

Answer 68

An R value is the ratio of the distance travelled by a solute to the distance travelled by the solvent. You can calculate it using this formula: R value of amino acid = distance travelled by solute / distance travelled by solvent When you’re measuring how far a solute has travelled, you measure from the point of origin to the vertical centre of the spot. You can work out what was in a mixture by calculating an R value for each solute and looking each R value up in a database, or table, of known values.

Biological molecules Flashcards

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