biological molecules long answer questions Flashcards
Describe how the structures of starch and glycogen are related to their functions (5marks)
Starch
- Helical so compact
- Insoluble so doesn’t affect water potential of plant cell
- Slightly branched for easy release of glucose for respiration
- Large molecule so cannot leave cell
Glycogen
- Compact granules
- Highly branched for quick release of glucose
- In animal cells which have higher respiration rates
How is the structures of cellulose related to its function (6 marks)
Cellulose is a POLYMER of beta glucose MONOMERS
polymers cross-linked by many hydrogen bonds
forms microfibrils
These are strong
Support plant cells and prevents bursting
Compare and contrast the structure and properties of starch and cellulose (5 marks)
BOTH are polysaccharides
STARCH is made of ALPHA GLUCOSE monomers whereas cellulose is made of BETA GLUCOSE monomers
in BOTH the monomers are linked by glycosidic bonds
In starch the polymers are slightly branched in contrast the polymers in cellulose are unbranched
BOTH are insoluble
In cellulose polymers are cross=linked by H bonds to form fibrils whereas in starch microfibrils do not form
Cellulose is a very strong molecule whereas starch is now strong
Starch is helical making it compact, cellulose isnt compact
The structure and functions of Phospholipids (7 marks)
Phospholipids made up of glycerol covalently bonded to 2 fatty acids and a phosphate group
Fatty acids are hydrophobic
Phosphate group is hydrophilic
Phospholipids main component of cell membranes
Phospholipids form a bilayer
Fatty acids face towards centre of membrane
Membrane PARTIALLY PERMEABLE
Membrane is a barrier to charged particles
Compare and contrast the structure and properties of triglycerides and phospholipids (5 marks)
Both contain ester bonds
Both contain glycerol
Fatty acids on both may be saturated or unsaturated
Both are insoluble in water
Both contain C, H, O but phospholipids also have P
Triglycerides have 3 fatty acides whereas phsopholipids have 2 fatty acids and a phosphate group
Triglycerides are hydrophobic in contrast phospholipids have hydrophilic and hydrophobic regions
Phospholipids form bilayers in water whereas triglycerides don’t
Describe chemical tests you could use to confirm the presence of lipids, non reducing sugars and amylase in a sample (5 marks)
Lipid
Add ethanol THEN add water AND mix
positive result is a white/milky EMULSION
Non-reducing Sugar
Do benedict’s test and get a negative result
BOIL with acid THEN neutralise with alkali
Heat w/ benedict’s and red/orange colour change is positive result
Amylase
Add biuret reagent and changes to purple
Add starch and test for reducing sugar
Describe the chemical reactions in the conversion of polymers to monomers and monomers to polymers. 2 named examples (5 marks)
A condensation reaction joins monomers together and forms a (chemical) bond and releases water
A hydrolysis reaction breaks a chemical bond between monomers and uses water
e.g Maltose is made of 2 alpha glucose monomers which are joined together by a glycosidic bond
Describe the induced fit mechanism of enzyme activity (5 marks)
Substrate and active site are not precisely complementary
Substrate induces shape change in active site of enzyme
Enzyme moulds itself around the substrate as the Enzyme substrate complex formed
Altered active site places a STRAIN on bonds in substrate
Lowering activation energy
Reaction takes place, product released
Use your knowledge of enzymes to compare and contrast the lock and key and induced fit models of enzyme activity (5 marks)
Both involve formation of ESCs
Both reduce activation energy
L&K substrate is complementary to active, IF substrate not complementary
IF active site changes shape to mould around substrate, this doesn’t happen in L&K
IF strain on bonds in enzyme and substrate, this doesnt happen in L&K
LK enzyme rigid whereas IF enzyme flexible
In both enzyme in not used up
In both enzyme is specific
In both enzyme can be affected by temp and pH
Compare and contrast competitive and non-competitive inhibitors (5 marks)
CI are a similar shape to the substrate whereas NCI are not
CI complementary to active site whereas NCI are not
CI bind to active site of enzyme in contrast NCI bind to enzyme outside of active site
With NCI the active site changes shape which does not happen with CI
Both prevent formation of ESCs
With CI the reaction rate increases if more substrate is added, this does not happen with NCI
Both reduce rate of reaction
How is the structure of DNA adapted to its function (5 marks)
It is able to carry the genetic code in its base sequence
Helical so it is compact
A large molecule which can carry a large amount of information
The sugar phosphate backbone is strong and stable due to strong covalent phosphodiester bonds
Many weak hydrogen bonds between the paired bases make the molecule strong and stable
The genetic code is protected inside the helix
The weak H bonds allow the two strands to separate during semi-conservative replication
Complementary base pairing allows precise replication
Compare and contrast the structures and functions of DNA and RNA (5 marks)
Both are composed of polymers of monomers called nucleotides
In both the nucleotides are joined together by phosphodiester bonds
Both contain the nitrogenous bases Adenine, Guanine and Cytosine
DNA nucleotides contain the base Thymine in contrast RNA nucleotides contain the base Uracil
DNA is double stranded whereas RNA is single stranded
DNA is a very long molecule, in contrast RNA is fairly short
Both can carry the genetic code in their base sequence
Both are involved in protein synthesis
DNA holds the genetic code inside the nucleus whereas mRNA carries the genetic code out of the nucleus to ribosomes
mRNA and tRNA are involved in translation whereas DNA is only involved in transcription
rRNA is used to build structures called ribosomes, DNA does not form structures
Compare and contrast DNA in Eukaryotic cells and DNA in Prokaryotic cells (5 marks)
The nucleotide structure is identical in both
In both the nucleotides are joined together by phosphodiester bonds
Eykaryotic DNA is longer than prokaryotic DNA
Eukaryotic DNA contains Introns whereas prokaryotic DNA does not
Eukaryotic DNA is linear whereas prokaryotic DNA is circular
Eukaryotic DNA is associated w/ proteins (histones) whereas prokaryotic DNA is not
DNA is mitochondira and chlorplasts is the same as DNA in prokaryotes
Describe how DNA is replicated (6 marks)
-Strands separate by enzyme DNA Helicase
-Both strands act as a template
-free nucleotides attach to the bases
-Complementary base pairing -A-T and G-C
-Enzyme DNA Polymerase joins nucleotides/ forms covalent bonds between nucleotides (to form new DNA strand)
-H bonds reform causing helix to form
- Semi-conservative replication: each new DNA molecule has one strand of original DNA and one new strand
Explain how ATP is able to act as the universal energy currency of living organisms (5 mark)
Releases energy when bonds between phosphate groups are broken
Energy release is quick/single hydrolysis reaction/immediate source of energy
Energy released in small manageable amounts
constantly regenerated/remade
can phosphorylate molecules and lower activation energy
provides energy for Active Transport
Provides energy for Protein Synthesis/DNA or RNA syntehsis
energy for movement plus example e.g. muscle contraction
H bonds between water molecules give water special properties. Outline these properties and their importance to living organisms (6 mark)
water has a high specific heat capacity, takes a large amount of energy to increase temperature of water
So it buffers temperature changes in aquatic ecosystems/ in the bodies of living organisms- Thermostability
water has a high latent heat of vaporisation so it takes a large amount of energy for liquid water to evaporate forming water vapour
Water acts as a coolant when it evaporates from body surfaces/sweating
Cohesion formed by H bonds between water molecules allow the flow of a continuous column of water up xylem vessels/surface tension for organisms such as pond skaters
Water can flow on mass so it acts as a transport medium e.g. blood plasma/phloem
Water is a solvent of polar substances allowing reactions to take place when reactants/enzymes and substrates move and collide in aqueous medium/dissolved in water or allows transport of dissolved solutes
Ice is less dense than liquid water so it floats allowing aquatic organisms to swim and feed in warmer deeper water/below the ice
The properties of water provide a very stable environment for aquatic life. These properties include:
the density of water decreases as its temperature falls below 4C so ice floats
Water acts as a solvent for polar substances such as nitrate ions
Water has a high specific heat capacity
Explain how these three properties help organisms to survive in a pond (6 mark)
Floating ice insulates the water below (preventing further cooling)
fish/animals able to move and feed in the warmer water below the ice
dissolved ions such as nitrates can circulate in water (convection currents)
more ions/nitrates available for plants which grow more
So more food/plants available to animals
water is a very thermostable environment
Enzymes/metabolic reactions able to work at optimum
Describe and explain how the process of centrifugation can be used to produce cell fractions containing pure nuclei, mitochondira and ribosomes (6marks)
tissue is chopped up and placed in a solution which is:
-isotonic to prevent osmosis which would cause organelles to burst or shrivel
-buffered to prevent any change in pH which would denature enzymes/proteins
-cold to reduce rate of enzyme which could damage organelles/reduce autolytic enzymes
tissue is homogensied to break open cells (releasing the organelles)
this tissue is then filtered to remove any large pieces of tissue
Placed in a centrifuge and spun at a high speed for a period of time so a pellet of nuclei forms
the remaining supernatant is centrifuged at a higher speed for longer so that the pellets contain mitochondria
centrifuge supernatant at higher speeds to obtain pellets of ribosomes.
How has the development of the electron microscope improved our understanding of cells (6marks)
the EM has a greater resolution
L> becuase the beam of electrons has a short wavelength
EM has a better magnification
Scanning EM allows 3D image to be seen
Able to see small organelles such as (any from ribosomes, Golgi body, vesicles etc)
Able to see internal structures of organelles such as (any from mitochondrial cristae, thylakoid membranes in chloroplasts, bacterial plasmids)
How do the organelles in a cell work together to produce and secrete a protein such as a antibody (5marks)
mRNA copy of DNA gene made in nucleus
-mRNA moves into cytoplasm through pores in the nuclear envelope
-mRNA attaches to ribosomes on the rough ER, the ribosomes make the protein
-Protein moves through the rough ER
-Protein enters golgi apparatus where it is modified and packaged into a vesicle
-vesicle carries protein to cell surface membrane where it is secreted (by exocytosis)
Some substances cross the cell surface membrane of a cell by simple diffusion through the phospholipid bilayer. Describe other ways by which substances cross this membrane 5m
By Osmosis: -from a high to low water potential/down water potential gradient
-through aquaporins/ water channels
By Facilitated diffusion: -Channel/carrier proteins
-down concentration gradient
By active transport: -carrier protein/protein pump
-againt concentration gradient
-using energy from ATP
The movement of substances across cell membranes is affected by membrane structure. Describe how 5m
-phospholipid bilayer allows diffusion of non polar/lipid soluble substances
-Phospholipid bylayer prevents diffusion of polar/charged/lipid soluble substances
-carrier proteins allow active transport
-channel/carrier proteins allow facilitated diffusion/cotransport
-shape/charge of carrier protein determines which substances are transported/move
-number of channel/carrier proteins determine how much movement
-membrane surface area determines how much movement
-cholesterol affects fluidity
