SCIENCE BIOLOGY_Sec3 (Chpt 3): Biological molecules Flashcards
1
Q
carbohydrates (def) [2pts]
A
- organic molecules made up of elements carbon, hydrogen and oxygen
- hydrogen and oxygen atoms present in ratio 2:1
2
Q
types of carbohydrates [3 types]
A
- single sugars (monosaccharides)
- double sugars (disaccharides)
- complex carbohydrates (polysaccharides)
3
Q
simple sugars
A
- monosaccharides
- can pass through partially permeable membrane (e.g. cell membrane)
4
Q
double sugars
A
disaccharides
5
Q
complex carbohydrates [2pts]
A
- polysaccharides
- complex macromolecules such as starch, glycogen and cellulose
6
Q
single sugars (3 examples)
A
- glucose
- fructose
- galactose
7
Q
double sugars (3 examples)
A
- maltose
- sucrose
- lactose
8
Q
single sugars: glucose (occurrence)
A
found in plants and animals
9
Q
single sugars: fructose (occurrence)
A
- fruit sugar
- common in plants, but rare in animals
10
Q
maltose (combination/formation)
A
formed by 2 glucose units
11
Q
sucrose (combination/formation)
A
formed by 1 glucose unit and 1 fructose unit
12
Q
lactose (combination/formation)
A
formed by 1 galactose unit and 1 glucose unit
13
Q
condensation reaction (def)
A
chemical reaction when two molecules combine together to form a single molecule with elimination of water molecule
14
Q
splitting of component [3pts + e.g.]
A
- undergo hydrolysis
- e.g. disaccharide split into component monosaccharides
- water molecule added to disaccharide to split it into component monosaccharides
- enzymes usually required
15
Q
complex carbohydrates: starch [6pts]
A
- structure: made up of several thousand glucose molecules joined together
- role: storage form of carbohydrates in plants
- when needed: can be digested to glucose to provide energy for cell activities
- found in storage organs of plants (e.g. potato tubers)
- not formed or stored by animals
- relatively insoluble and thus ideal for storage
16
Q
complex carbohydrates: cellulose [5pts]
A
- structure: made up of many glucose molecules joined together
- bond together between glucose unit are different from that in starch
- role: cellulose cell wall protects plant cells from bursting or damage
- cellulose cannot be digested in our intestines (serve as dietary fibre that prevents constipation)
- occurrence: present in cell walls of plants
17
Q
complex carbohydrates: glycogen [4pts]
A
- structure: branched molecule, made up of many glucose molecules joined together
- role: storage form of carbohydrates in mammals
- when needed: digested to glucose to provide energy for cell activities
- occurrence: stored in liver and muscles of mammals
18
Q
reasons why glycogen and starch are ideal for storage in cells [4pts]
A
- insoluble in water: does not change water potentials in cells
- cannot pass through cell membrane (will not be lost from cells)
- can be broken down easily to glucose when needed
- highly compact: occupy less space than individual glucose molecules that form them
19
Q
digestion of starch into single sugars [3pts + two stages]
A
- digestion of starch into glucose involves diff. stages
- each stage requires diff. enzyme to break down chemical bonds within specific carbohydrate molecules
- hydrolysis reaction breaking down bonds of starch and maltose to form glucose molecules with help of enzymes
First stage: enzyme amylase hydrolyses (or breaks down) starch molecules into maltose molecules
Second stage: enzyme maltase hydrolyses (or breaks down) maltose molecules into glucose molecules
20
Q
functions of carbohydrates: source of energy
A
substrate for respiration to provide energy for cell activities
21
Q
functions of carbohydrates: forming supporting structures
A
some carbohydrates are able to form supporting structures
e.g. cellulose in cell walls of plants
22
Q
functions of carbohydrates: conversion to other organic compounds
A
excess carbohydrates can be converted into amino acids and fats
23
Q
functions of carbohydrates: formation of nucleic acids
A
forming nucleic acids, e.g. DNA
24
Q
functions of carbohydrates: production of nectar
A
used to produce nectar in flowers
25
functions of carbohydrates: synthesis lubricants
involves in forming lubricants, e.g. mucus
26
Types of carbohydrates [2 types]
1. Reducing sugars
2. Starch
27
Carbohydrates - reducing sugars [example]
- glucose
- fructose
- maltose
28
Testing reagent for reducing sugars
benedict’s solution
29
Benedict’s solution description [3pts]
- some sugars: reducing properties, will produce red precipitate when boil with Benedict’s solution
- contains copper (II) sulfate, blue in colour: can be reduced to red precipitate of copper (I) oxide by these sugars (reducing sugars)
- test is semi-quantitative: can give approximate indication of how much reducing sugars is present
30
Benedict’s solution procedure
add an equal volume of Benedict’s solution to the sample in a test tube. Place the test tube in a hot water bath for a few minutes
31
Benedict’s solution: Amount of reducing sugars is + colour change
Reducing sugars absent: solution remains blue
Tiny amount: Blue to green precipitate
Moderate amount (low concentration) : blue to yellow or orange precipitate
Large amount (high concentration): blue to brick-red precipitate
32
Testing reagent for starch
iodine solution
33
Iodine solution [2pts]
- add a few drops of iodine solution to food sample
- brown iodine solution changes to blue-black when starch is present
34
Fats [6pts]
- type of lipid
- organic compounds made up of carbon, hydrogen and oxygen
- contain lesser number of O atoms in proportion to H atoms —> hence no generalised formula
- need more oxygen and are less efficient in releasing energy than carbohydrates
- made up of one glycerol molecule and three fatty acid molecules
- can be animal or plant fats
35
Examples of sources of fats
- food rich in fats (e.g. butter, cheese, fatty meat, nuts, peas, beans, palm oil)
- meat of most fish and ‘white meats’ (e.g. chicken and turkey) contain relatively less fats, but some fish (e.g. salmon, herring) have more fats
36
Functions of fats [5pts]
1. Energy
2. Insulation
3. Solvent
4. Prevention of water loss
5. Constituent of protoplasm
37
Function of fats - energy/ storage of energy [3pts]
- source of energy
- serve as long-term energy storage in body
- have higher energy value compared to carbohydrates
38
Functions of fats - insulation [2pts + e.g.]
- natural insulating material
- prevent excessive heat loss
- e.g. whales have blubber (fats) to keep them warm in freezing ocean temperatures
39
Functions of fats - solvent [1pt]
solvent for certain vitamins and hormones
40
Functions of fats - prevention of water loss [3pts]
- oil substance (secreted by glands in skin): helps reduce water loss from skin surface
- forms thin layer over skin surface to reduce rate of evaporation of water
- reduces rate of heat loss from skin: acts as insulating layer
41
Functions of fats - constituent of protoplasm [1pt]
essential part of cells, especially in cell membranes
42
Testing for fats
Ethanol emulsion test
43
Test for fats: ethanol emulsion test procedure
add an equal volume of ethanol to the sample in a test tube. Mix thoroughly and add an excess of water
44
Test for fats (ethanol emulsion test) results
- contents of test tube remain clear: fats absent
- white emulsion formed (ethanol and water added to fats): fats present
45
Proteins [3pts]
- organic substances made up of carbon, hydrogen, oxygen, nitrogen (sulfur and phosphorus: may be present)
- always present in all cells
- largest and most complex of all food substance
46
amino acids
- building blocks of proteins
- each amino acid has simple basic structure:
1. Amino group (—NH₂)
2. Acidic group (—COOH)
3. Side chain
- 20 different naturally occurring amino acids: different side chains
47
Diff amino acids join tgt through…
Peptide bonds in linear sequence to form polypeptide
48
Diff polypeptides join tgt to form…
even longer chain of amino acids
49
One or more longer chains of amino acids can then…
interact and combine to form protein molecule that is folded into more complex, three-dimensional (3-D) shape
50
Examples of sources of proteins
1. Animal: milk, eggs, seafood, meat
2. Plants: soya beans, nuts, grains, vegetables
51
Functions of proteins [3pts]
1. Synthesis of new cytoplasm, for growth and repair of worn-out cells
2. Synthesis of enzymes and some hormones
3. Formation of antibodies to fight diseases
52
Test for proteins
biuret test
53
Biuret solution
blue solution which consists of sodium hydroxide and copper (II) sulfate
54
Biuret test procedure
add equal volume of NaOH solution to sample in a test tube. Add a few drips of 1% CuSO₄ solution. Shake and mix well.
OR
Add equal volume of biuret solution to sample in a test tube
55
Biuret test results + conclusions
solution remains blue: proteins absent
Solution turns violet (or deep purple): proteins present
56
