Biological Molecules Flashcards
Why is water a polar molecule?
Because of the unequal distribution of electrons (polarity) despite being covalent. The electrons are pulled towards oxygen so it’s slightly negative while the hydrogens are slightly positive.
Why are water molecules cohesive?
The polarity (unequal distribution of electrons making the oxygen negative and hydrogen positive) means the molecules stick together with hydrogen bonds.
How many hydrogen bonds can water make in solid, liquid and gas form? Why?
Ice - 4 bonds
Liquid- 2 or 3 because they’re always moving past each other and breaking and reforming due to the weak hydrogen bonds.
Gas- 0
What’s adhesion and how does this as well as cohesion help in a xylem vessel?
The polar water molecules sticking to another material with polar properties (slightly positive or negative).
In a xylem, the vessel walls are polar so water molecules are attracted to it. This and the attraction of the water molecules to each other (cohesion) helps to transport water up the leaves in a capillary action.
Why is water a polar solvent?
It will dissolve things that are polar (glucose) and ionic (salt).
Why will water dissolve things that are ionic as well as polar?
The positive end of the water molecule (hydrogen) will be attracted to the negative ion and the negative end of the water molecule (oxygen) will be attracted to the positive ion.
This means ions will be totally surrounded by water molecules and they’ll dissolve.
Why is water used as a transport medium? Give examples
Because it’s a solvent and metabolite (involved in many metabolic reactions).
Plants- xylem, phloem
Animals- plasma in the blood
Why does water provide a stable environment for organisms to live in.
Because it’s thermostable: buffers/resists change in temp
It has a high specific heat capacity so needs lots of energy to raise the temperature of 1kg by 1 degree.
Why does water have a high latent heat of vaporisation from liquid to gas?
Why does hand sanitiser make your hands cold?
Because a lot of energy is needed to break the hydrogen bonds between water molecules and change the state.
Molecules with enough energy evaporate, carrying heat away (evaporation causes cooling).
What allows aquatic plants and algae to photosynthesise?
The transparency of water.
Why does ice float?
As water freezes it expands (molecules held further apart by hydrogen bonds) so frozen water is less dense than liquid (which has less hydrogen bonds) and therefore floats.
The frozen ice layer insulates the water below so the water below doesn’t freeze (allowing some organisms to survive).
Give 6 examples of inorganic ions biological significance in organisms.
IRON IONS- found in haemoglobin where they play a role in the transport of oxygen and are used in ferrodoxin in photosynthesis and is an electron carrier in some bacteria.
PHOSPHATE IONS- play a structural role in DNA molecules as the sugar-phosphate backbone of DNA structure.
Bonds between phosphate ions store energy in ATP molecules.
Phospholipids make up the plasma membrane.
HYDROGEN IONS- important in determining the PH of solutions and therefore the functioning of enzymes.
SODIUM IONS- important in the transport of glucose + amino acids across plasma membranes and they generate resting and action potentials in neurons.
NITROGEN- used in chlorophyll.
CALCIUM- an extracellular component of bone matrix.
It forms an exoskeleton.
It stimulates synaptic transmission between neurons and is used in muscle contraction.
What does water dissolve as a solvent?
Gases (oxygen, carbon dioxide)
Wastes (ammonia + urea)
Inorganic ions + small hydrophilic molecules (amino acids, monosaccharides + ATP)
Enzymes who’s reactions take place in solution.
Water in metabolism
Used to break down complex molecules by hydrolysis (proteins to amino acids).
Produced in condensation reactions.
Chemical reactions take place in aqueous solutions.
It’s a Major raw material in photosynthesis.
What do organic compounds have and why are they non-polar?
Organic compounds have C-H bonds.
They’re non-polar because the electrons are evenly distributed.
Why are a large number of types and sizes of molecule all based on carbon?
Carbon atoms very readily form bonds with other carbon atoms which allows a sequence of carbon atoms of various lengths to be built up. These form a backbone along which other atoms can be attached.
How do monomers and polymers link and give examples of both.
Monomers are individual molecules which join in long chains called polymers.
Carbohydrates-The monomers monosaccharides join in chains to make polysaccharides.
The monomers amino acids join in chains to make proteins.
The monomers nucleotides join to make the polymers nucleic acids (DNA and RNA).
Glycerol and fatty acids join to make triglycerides (fat).
What four elements are most polymers made up of?
Carbon, hydrogen, oxygen and nitrogen.
Monosaccharides definition and examples
E.g. glucose, galactose and fructose.
Monosaccharides (simple sugars) are sweet, soluble substances (organic molecules) that act as building blocks for more complex carbs (polysaccharides).
What’s a disaccharide and how is it made?
A disaccharide is the combination of two monosaccharides.
A disaccharide is formed through a condensation reaction: when the monosaccharides join, a molecule of water is removed and the bond formed is called a glycosidic bond.
What’s the opposite of a condensation reaction?
A hydrolysis reaction.
When water is added to a disaccharide (or polysaccharide) it breaks the glycosidic bond releasing the monosaccharides.
What’s the general formula for a monosaccharide?
(CH2O)n
n= number of carbon atoms (3-7)
Glucose
A monosaccharide.
Glucose is a hexose (6 carbons sugar) with the formula C6H12O6.
Glucose has two isomers (same chemical formula but different arrangement of atoms): alpha glucose and beta glucose.
What’s a reducing sugar?
Reducing sugars are sugars that can donate electrons (or reduce) another chemical (in the case of the practical: Benedict’s reagent) (OILRIG).
All monosaccharides and some disaccharides (except sucrose) are reducing sugars.
What happens to the Benedict’s reagent when it’s heated in a water bath with a reducing sugar?
Benedict’s reagent is an alkaline solution of copper (II) sulphate. When a reducing sugar is heated with the Benedict’s reagent it forms an insoluble red precipitate of copper (I) oxide.
Electrons are donated from the reducing sugar to the Benedict’s reagent.
Cu2+ + e- = Cu+
How to make the non-reducing sugar sucrose (disaccharide) int two monosaccharides to make it a reducing sugar.
If the Benedict’s reagent stayed blue it’s a non-reducing sugar.
- To make sucrose a reducing sugar you perform hydrolysis by adding hydrochloric acid and heating in a water bath for 5 mins. This should separate the disaccharide into two monosaccharides making two reducing sugars.
- Then add neutraliser (sodium hydrogen carbonate) until it stops fizzing and is alkaline (or use litmus paper).
- Retest the resulting solution by heating with 2cm3 of Benedict’s reagent in a water bath for 5 mins.
If a non-reducing sugar as present in the original sample the Benedict’s will turn orange-brown. This is due to the reducing sugars that were produced from the hydrolysis of the non-reducing sugar.
Disaccharide examples
Glucose + glucose = maltose
Glucose + fructose = sucrose
Glucose + galactose = lactose
What are polysaccharides?
Soluble or insoluble? Why?
What happens when they’re hydrolysed?
Give 2 examples.
- Polysaccharides are polymers formed by combining together many monosaccharides that are joined by glycosidic bonds through a condensation reaction.
- Polysaccharides are insoluble as they’re very large molecules which make them suitable for storage.
- When hydrolysed they break down into disaccharides or monosaccharides.
- Starch is found in many parts of plants (in form of granules or grains) e.g. chloroplast. It’s formed by the joining of 200-100,000 alpha glucose molecules by glycosidic bonds in a series of condensation reactions.
- Cellulose gives structural support to plant cells.
Test for starch.
Starch is easily detectable as it changes the colour of iodine in potassium iodide from yellow to blue/black.
- Put 2cm3 of the sample in a test tube or 2 drops into spotting tiles.
- Add 2 drops of iodine solution + shake or stir.
- Presence of starch = blue/black.
How is starch suited to its role in energy storage?
- Insoluble, doesn’t effect water potential, so water isn’t drawn into the cells by osmosis.
- large and insoluble, doesn’t diffuse out of cells.
- compact, so a lot of it can be stored in a small space.
- When hydrolysed it forms alpha glucose which is both easily transported and readily used in respiration.
- the branched form has many ends, each of which can be acted on by enzymes simultaneously meaning glucose monomers are released very rapidly.
What two polysaccharides is starch made up of?
Amylose and amylopectin
Amylose
This and amylopectin make up starch
- Formed by alpha glucose monomers.
- alpha 1,4 glycosidic bonds between the monomers.
- The chain forms a coiled shape.
Amylopectin
This and amylose make up starch.
- Formed from alpha glucose monomers.
- alpha 1,4 and alpha 1,6 glycosidic bonding between the monomers.
- Branch shape due to the extra alpha 1,6 glycosidic bonding.
- More branches: more easily hydrolysed (because there’s more places where the enzyme can work) to glucose or maltose to provide energy when needed.
Glycogen. Where found? Structure Main role How stored and where found in body?
- Found in animal, fungi and bacterial cells.
- Very similar structure to amylopectin.
- formed from chains of monosaccharide alpha glucose but there’s less alpha 1-4 glycosidic bonds and more alpha 1,6 glycosidic bonds (because it’s highly branched so produces lots of glucose).
- Main role: energy storage.
- Also in small granules (like starch), found mainly in the muscles and liver.
- Animals need more glucose than plants because they’re more active so they have more branches in glycogen than in starch.
Starch and glycogen similarities.
-Joining of alpha glucose.
Compact- so a lot can be stored in little space, due to their structure (coiled like a slinky).
-Provide easy access to glucose (energy source)- glucose released by hydrolysis of glucose molecules from multiple ends (branches).
-Large and insoluble so it doesn’t diffuse out of cells or affect the water potential.
How is the structure of cellulose suited to its function of providing support and rigidity?
How does the cellulose cell wall prevent the cell from bursting as water enters it by osmosis?
- Cellulose molecules are made up of beta glucose and so form long straight, unbranched chains.
- These cellulose molecular chains run parallel to each other and are crossed linked by weak hydrogen bonds which add collective strength.
- These molecules are grouped to form microfibrils which in turn are grouped to form fibres all of which provide more strength.
-By exerting an inward pressure that stops any further influx of water. As a result, living plant cells are turgid and push against one another, making non-woody parts of the plant semi-rigid. This is important in maintaining stems and leaves in a turgid state so they can provide the maximum surface area for photosynthesis.
Lipids characteristics
- They contain carbon, hydrogen and oxygen.
- The proportion of oxygen to carbon and hydrogen is smaller than in carbohydrates.
- non-polar due to large % of Cs and Hs and so are Insoluble in water (hydrophobic).
- Soluble in organic solvents such as alcohols and acetone.
Roles of lipids
- Phospholipids contribute to the flexibility of membranes and the transfer of lipid-soluble substances across them.
- source of energy (when oxidised, lipids provide more than twice the energy as the same mass of carbohydrates + release valuable water.
- Waterproofing (they’re insoluble in water + therefore good for waterproofing. Plants and insects have waxy lipid cuticles that conserve water while mammals produce an oily secretion from the sebaceous glands in the skin).
- Insulation (fats are slow conductors of heat + when stored beneath body surface help to retain body heat. Also act as electrical insulators in the myelin sheath).
- protection (fat is often stored around delicate organs such as the kidney).
Properties of saturated fatty acids.
E.g. meats, butter, dairy.
- Contain only C-C bonds (no double bonds between carbon atoms because all the carbon atoms are linked to the maximum possible number of hydrogen atoms) so form linear hydrocarbon chains.
- Fatty acids can pack closely together.
Strong attraction between fatty acid chains.
-High melting points
-Solid at room temp.
