Biological Molecues Flashcards
Describe the basic function and structure of starch and glycogen
starch
Polysaccharide of a glucose
Some has 1.4 glucosidic bonds so in unbranched
Some has 1,4- and 1,6-glycosidic bonds so is branched (amylopectin)
Glycogen
Polysaccharide made of a-glucose
• 1,4- and 1,6-glycosidic bonds → branched
Explain how the structures of starch and glycogen relate to their functions
Starch (amylose)
Helical → compact for storage in cell
Large, insoluble polysaccharide molecule → can’t leave cell / cross cell membrane
Insoluble in water → water potential of cell not affected (no osmotic effect)
Glycogen
Branched → compact / fit more molecules in small area
Branched → more ends for faster hydrolysis → release glucose for respiration to make ATP for energy release
Large, insoluble polysaccharide molecule → can’t leave cell / cross cell membrane
Insoluble in water → water potential of cell not affected (no osmotic effect)
Suggest a method to measure the quantity of sugar in a solution
Carry out Benedict’s test as above, then filter and dry precipitate
• Find mass / weight
Suggest another method to measure the quantity of sugar in a solution
Make sugar solutions of known concentrations (eg. dilution series)
2. Heat a set volume of each sample with a set volume of Benedict’s solution for the same time
3. Use colorimeter to measure absorbance (of light) of each known concentration
4. Plot calibration curve - concentration on x axis, absorbance on y axis and draw line of best fit
5. Repeat Benedict’s test with unknown sample and measure absorbance
6. Read off calibration curve to find concentration associated with unknown sample’s absorbance
How do enzymes act as biological catalysts?
Each enzyme lowers activation energy of reaction it catalyses
• To speed up rate of reaction
Describe the induced-fit model of enzyme action
Substrate binds to (not completely complementary) active site of enzyme
2.
3.
Causing active site to change shape (slightly) so it is complementary to its substrate
So enzyme-substrate complex forms
4. Causing bonds in substrate to bend / distort, lowering activation energy
Describe how models of enzyme action have changed over time
Initially lock and key model (now outdated)
• Active site a fixed shape, complementary to one substrate
• Now induced-fit model
Explain the specificity of enzymes
Specific tertiary structure determines shape of active site
° Dependent on sequence of amino acids (primary structure)
: Active site is complementary to a specific substrate
Only this substrate can bind to active site, inducing fit and forming an enzyme-substrate complex
Describe and explain the effect of enzyme concentration on the rate of enzyme-controlled reactions
As enzyme concentration increases, rate of reaction increases
° Enzyme concentration = limiting factor (excess substrate)
More enzymes so more available active sites
So more enzyme-substrate complexes form
At a certain point, rate of reaction stops increasing / levels off
Substrate concentration = limiting factor
Describe and explain the effect of substrate concentration on the rate of enzyme-controlled reactions
• As substrate concentration increases, rate of reaction increases
• Substrate concentration = limiting factor (too few substrate molecules to occupy all active sites)
• More enzyme-substrate complexes form
• At a certain point, rate of reaction stops increasing / levels off
• Enzyme concentration = limiting factor
• As all active sites saturated / occupied
Suggest how the structure of DNA relates to its functions
Two strands → both can act as templates for semi-conservative replication
Hydrogen bonds between bases are weak → strands can be separated for replication
Complementary base pairing - accurate replication
• Many hydrogen bonds between bases → stable / strong molecule
Double helix with sugar phosphate backbone - protects bases / hydrogen bonds
• Long molecule → store lots of genetic information (that codes for polypeptides)
Double helix (coiled) - compact
Describe the structure of ATP
Ribose bound to a molecule of adenine (base) and 3 phosphate groups
• Nucleotide derivative (modified nucleotide)
Describe how ATP is broken down
• ATP (+ water) → ADP (adenosine diphosphate) + pi (inorganic phosphate)
• Hydrolysis reaction, using a water molecule
• Catalysed by ATP hydrolase
Give two ways in which the hydrolysis of ATP is used in cells
Coupled to energy requiring reactions within cells (releases energy)
• eg. active transport, protein synthesis
• Inorganic phosphate released can be used to phosphorylate (add phosphate to) other compounds, making them more reactive
Describe how ATP is resynthesised in cells
• ADP + Pi → ATP (+ water)
Condensation reaction, removing a water molecule
Catalysed by ATP synthase (enzyme)
• During respiration and photosynthesis
Suggest how the properties of ATP make it a suitable immediate source of energy for cells
Releases energy in (relatively) small amounts / little energy lost as heat
Single reaction / one bond hydrolysed to release energy (so immediate release)
Cannot pass out of cell
Explain 5 properties of water that are important in biology
Metabolite
Used in condensation / hydrolysis / photosynthesis / respiration
Solvent
1. Allows metabolic reactions to occur (faster in solution)
2. Allows transport of substances eg. nitrates in xylem, urea in blood
(Relatively) high specific heat capacity
• Buffers changes in temperature
As can gain / lose a lot of heat / energy without changing temperature
1. Good habitat for aquatic organisms as temperature more stable than land
2. Helps organisms maintain a constant internal body temperature
(Relatively) large latent heat of vaporisation
• Allows effective cooling via evaporation of a small volume (eg. sweat)
• So helps organisms maintain a constant internal body temperature
Strong cohesion between water molecules
Supports columns of water in tube-like transport cells of plants eg. transpiration stream through xylem in plants
2. Produces surface tension where water meets air, supporting small organisms
Describe the role of hydrogen, ions
Hydrogen ions (H*)
Maintain pH levels in the body → high concentration = acidic / low pH
Affects enzyme rate of reaction as can cause enzymes to denature
Iron ions
Iron ions (Fe?*)
Component of haem group of haemoglobin
Allowing oxygen to bind / associate for transport as oxyhaemoglobin
Sodium ions
Sodium ions (Na*)
Involved in co-transport of glucose / amino acids into cells
2. Involved in action potentials in neurons
3. Affects water potential of cells / osmosis
Phosphate ions
Phosphate ions (PO,*)
1. Component of nucleotides, allowing phosphodiester bonds to form in DNA / RNA
2. Component of ATP, allowing energy release
3. Phosphorylates other compounds making them more reactive (topic 1.6)
4. Hydrophilic part of phospholipids, allowing a bilayer to form
Where are inorganic ions found in the body?
In solution in cytoplasm and body fluid, some in high concentrations and others in very low concentrations
