Biology exam questions - biological molecules Flashcards
Describe a biochemical test to show that raffinose solution contains a
non-reducing sugar
- heat with acid and neutralise
- heat with benedict’s solution
- red/ orange precipitate formed
A student carried out the Benedict’s test. Suggest a method, other than
using a colorimeter, that this student could use to measure the quantity of
reducing sugar in a solution.
- filter and dry precipitate
- find the mass
Lactulose is a disaccharide formed from one molecule of galactose and
one molecule of fructose.
Other than both being disaccharides, give one similarity and one difference
between the structures of lactulose and lactose.
similarity - both contain galactose
difference - lactulose contains fructose whereas lactose contains glucose
Describe two differences between the structure of a cellulose molecule
and a glycogen molecule.
-Cellulose is made up of β-glucose (monomers) and glycogen is
made up of α-glucose (monomers);
-Cellulose molecule has straight chain and glycogen is
branched;
- glycogen has 1,4- and 1,6- glycosidic bonds and cellulose has
only 1,4- glycosidic bonds;
Describe and explain two features of starch that make it a good storage
molecule
Insoluble (in water), so doesn’t affect water potential;
coiled / (α-)helix so can fit many (molecules) in
small area;
4. Branched / more ends for fast breakdown / enzyme action
Describe the structure of glycogen.
polysaccharide of alpha glucose
joined by glycosidic bonds
2 marks
Explain one way in which starch molecules are adapted for their function in
plant cells
Insoluble;
Don’t affect water potential
2 marks
Explain how cellulose molecules are adapted for their function in plant
cells.
Long and straight chains;
Become linked together by many hydrogen bonds to form
fibrils;
Provide strength (to cell wall).
a) Describe how an ATP molecule is formed from its component molecules
- made from adenine, ribose and three phosphates
- condensation reaction
- catalysed by ATP synthase enzyme
The new antibiotic is safe to use in humans because it does not inhibit the
ATP synthase found in human cells.
Suggest why human ATP synthase is not inhibited and bacterial synthase
is inhibited
Human ATP synthase has a different shape active site to
bacterial ATP synthase
ATP is an energy source used in many cell processes. Give two ways in
which ATP is a suitable energy source for cells to use.
Releases energy instantaneously;
Phosphorylates other compounds, making them more reactive;
Can be rapidly re-synthesised;
Is not lost from / does not leave cells
( max 2) .
Describe how ATP is resynthesised in cells.
- from ATP and inorganic phosphate
- from ATP synthase
Give two ways in which the hydrolysis of ATP is used in cells.
- to release energy for respiration’
- to add inorganic phosphate to compounds to make them more reactive
Describe the structure of DNA
Polymer of nucleotides;
Each nucleotide formed from deoxyribose, a phosphate (group) and
an organic/nitrogenous base;
Phosphodiester bonds (between nucleotides);
Double helix/2 strands held by hydrogen bonds;
(Hydrogen bonds/pairing) between adenine, thymine and
cytosine, guanine
Describe how a phosphodiester bond is formed between two nucleotides
within a DNA molecule
Condensation (reaction)/loss of water;
(Between) phosphate and deoxyribose;
(Catalysed by) DNA polymerase;
max two
In the process of semi-conservative DNA replication, the two strands within
a DNA molecule are separated. Each then acts as a template for the
formation of a new complementary strand.
Describe how the separation of strands occurs.
DNA helicase;
Breaks hydrogen bonds between bases ( complementary base pairs)
Describe the role of DNA polymerase in the semi-conservative replication
of DNA.
Joins (adjacent DNA) nucleotides;
(Catalyses) condensation (reactions);
(Catalyses formation of) phosphodiester bonds (between adjacent nucleotides);
max two
Name the two scientists who proposed models of the chemical structure of
DNA and of DNA replication
Watson and Crick
Use your knowledge of semi-conservative replication of DNA to suggest:
1. the role of the single-stranded DNA fragments
Act as a template strand
Use your knowledge of semi-conservative replication of DNA to suggest the role of DNA nucleotides
form complementary base pairs with bases on template strand
Give two features of DNA and explain how each one is important in the
semi-conservative replication of DNA.
Weak / easily broken hydrogen bonds between bases allow two
strands to separate / unzip;
Two strands, so both can act as templates;
may appear in the same feature
Complementary base pairing allows accurate replication;
