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Biology > Unit 1: Biological Molecules > Flashcards

Unit 1: Biological Molecules Flashcards

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AP® Biology flashcards Biology 101 flashcards
1
Q

Define a monomer - with examples

A

Monomers are small, basic molecular units. They can join together to form larger molecules (polymers)
Examples: monosaccharides (glucose, fructose and galactose), amino acids and nucleotides

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2
Q

Define polymers - with examples

A

Polymers are large, complex molecules composed of long chains of monomers joined together.
Examples: polysaccharides, proteins, DNA/RNA and most carbohydrates.

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3
Q

What happens in a condensation reaction?

A

A chemical bond forms between 2 molecules and 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 bod between 2 molecules.

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5
Q

What are the 3 heroes monosaccharides?

A
  • glucose
  • fructose
  • galactose

All have the molecular formula: C6H12O6

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6
Q

What type of bond is formed when monosaccharides react?

A

(1,4 or 1,6) glycosidic bond.
2 monomers = 1 chemical bond = disaccharide
Multiple monomers = many chemical bonds = polysaccharide

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7
Q

What are 3 disaccharides and how are they formed?

A
  • maltose: glucose + glucose
  • sucrose: glucose + fructose
  • lactose: glucose + galactose

A condensation reaction forms glycosidic bond between two monosaccharides.
All have the molecular formula: C12H22O11

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8
Q

What elements do all carbohydrates contain?

A

C, H and O

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9
Q

What type of sugar is glucose?

A

Hexose

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10
Q

What are the two types of glucose?

A

Alpha and beta
They are isomers (molecules with the same molecular formula as each other, but with the atoms connected in a different way)

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11
Q

What the difference between alpha and beta glucose?

A

Alpha glucose has H on top and OH at bottom at right group
Beta glucose has OH on top and H at bottom at right group

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12
Q

What’s the test for presence of sugars?

A

Benedict’s test

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13
Q

Describe the test for presence of reducing sugars

A
  1. Reducing sugars include all monosaccharides and some disaccharides (e.g. maltose and lactose).
  2. Add Benedict’s reagent (blue) to a sample and heat it in a water bath that has been brought to a boil (100 degrees for 5 mins).
  3. If test is positive it will form a coloured precipitate (solid particles suspended in the solution)
    -> colour of precipitate changes from: blue - green - yellow - orange - brick red
  4. The higher the conc 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 weight the precipitate.

always use an excess of Benedict’s solution - this makes sure that all the sugar reacts

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14
Q

Describe the test for the presence of non-reducing sugars

A
  1. If result of reducing sugars is negative, non-reducing sugars could still be present, such as sucrose. To test for them 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 water bath that’s been brought to a boil (100 degrees for 5 mins). You then neutralise it with sodium hydrogen-carbonate. Then just carry out the Benedict’s test as you would for a reducing sugar.
  3. If the test is positive it will form a coloured precipitate (as it did for reducing sugars). If test is negative the solution will stay blue, which means it doesn’t contain sugar (either reducing or non-reducing).
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15
Q

Describe the structure and functions of starch

A

Storage polymer of a-glucose in plant cells
- insoluble = no osmotic effect on cells
- large = doesn’t diffuse out of cells

Made from amylose:
- 1,4 glycosidic bonds
- unbranched chain of a-glucose
- helix (coiled) with intermolecular H-bonds = compact -> good for storage - fit more in smaller space.

Made from amylopectin:
- 1,4 & 1,6 glycosidic bonds
- branched = many terminal ends for hydrolysis into glucose

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16
Q

What’s the test for presence of starch?

A

The iodine test

17
Q

Describe the test for the presence of starch

A
  1. Add iodine dissolved in potassium iodide solution to the test sample.
  2. If starch is present, the sample changes colour from browny-orange to a blue-black colour.
  3. If starch isn’t present the colour remains browny-orange.
18
Q

Describe the structure and functions of glycogen

A

Main storage polymer of a-glucose in animal cells (but also found in plant cells)
- 1,4 & 1,6 glycosidic bonds
- branched = many terminal ends for hydrolysis, stored glucose can be released quickly -> important for energy release in animals
- insoluble = no osmotic effect & does’t diffuse out of cells
- compact -> good for storage

19
Q

Describe the structure and functions of cellulose

A

Polymer of B-glucose gives rigidity to plant cells walls (prevents bursting under turgor pressure, holds stem up)
- 1,4 glycosidic bonds
- straight-chain, unbranched molecule
- alternate glucose molecules are rotated 180 degrees
- H-bonds crosslinks between parallel strands form microfibrils = high tensile strength (structural support for cells e.g. plant cell walls)

20
Q

Outline how colorimetric could be used to give qualitative results for the presence of sugars and starch

A
  1. Make standard solutions with known concentrations. Record absorbance or % transmission values.
  2. Plot calibrations curve: absorbance or % transmission (y-axis), concentration (x-axis)
  3. Record abundance or % transmission values of unknown samples. Use calibration curve to read off concentration
21
Q

What’s the structure of a triglyceride?

A

One molecule of glycerol with three fatty acids attached to it

Fatty acid molecules have long ‘tails’ made up of hydrocarbons - they’re ‘hydrophobic’ (repel water molecules). They make lipids insoluble in water.
All fatty acids have the same basic structure, but hydrocarbon tail varies (variable ‘R’ group)

22
Q

How do triglycerides form?

A

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

23
Q

Contrast saturated and unsaturated fatty acids

A

Saturated:
- contain only single bonds
- straight-chain molecules have many contact points
- higher melting point = solid at room temp
- found in animal fats
- ‘saturated’ with hydrogen

Unsaturated:
- contain C-C double bonds
- ‘Kinked’ molecules have fewer contact points
- lower melting point = liquid at room temp
- found in plant oils

24
Q

Relate the structure of triglycerides to their functions

A
  • long hydrocarbon tail contain lots of chemical energy = load of energy is released when they’re broken down.
  • high energy: mass ratio = high calorific value from oxidation (energy storage)
  • insoluble hydrocarbon chain = no effect on water potential of cells & used for waterproofing. The triglycerides clump together as insoluble droplets in cells because the fatty acid tails = hydrophobic - they face inwards, shielding themselves from water with there glycerol heads
  • slow conductor of heat = thermal insulation e.g. adipose tissue
  • less dense than water = buoyancy of aquatic animals
25
Q

Describe the structure and function of phospholipids

A

Amphipathic molecule: glycerol backbone attached to 2 hydrophobic fatty acid tails & 1 hydrophilic phosphate head.
- forms phospholipid bilayer in water = component of membranes
- tails can splay outwards = waterproofing

26
Q

How does the structure of phospholipids relate to their functions?

A
  • make up the bilayer of cell membranes = which control what enters and leaves a cell
  • heads are hydrophilic and tails are hydrophobic = they form a double layer with their heads facing out towards the water on either sides.
  • centre of bilayer is hydrophobic = water-soluble substances cant easily pass through - membrane act as a barrier to those substances
27
Q

Compare phospholipids and triglycerides

A
  • both have glycerol backbone
  • both may be attached to a mixture of saturated, monounsaturated & polyunsaturated fatty acids
  • both contain the elements: C, H, O.
  • both formed by condensation reactions
28
Q

Contrast phospholipids and triglycerides

A

Phospholipids:
- 2 fatty acids & 1 phosphate group attached
- hydrophilic head & hydrophobic tail
- used primarily in membrane formation

Triglycerides:
- 3 fatty acids attached
- entire molecule is hydrophobic
- used primarily as a storage molecule (oxidation releases energy)

29
Q

Are phospholipids and triglycerides polymers?

A

No: they aren’t made from small repeating units. They are macromolecules.

30
Q

What’s the test for the presence of lipids?

A

The Emulsion test

31
Q

Describe the test for the presence of lipids

A
  1. Shake the test substance with ethanol for about a minute so it dissolves.
  2. Add an equal volume of water and shake again
  3. If lipids are present, a milky white emulsion forms
  4. The more lipid there is, the more noticeable the milky colour will be

Biology (6 decks)

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