Biological Molecules Flashcards
What are the functions of water?
- Water is a reactant (part of many reactions e.g. hydrolysis)
- Water is a solvent (many substances dissolve in it e.g. ions in water into the blood and many biological reactions take place in a solution)
- Water transports (substances e.g. glucose, mineral ions, oxygen gas)
- Water is involved in temperature control (has high specific heat capacity and high latent heat of evaporation)
- Water is a habitat (contains oxygen and nutrients can be dissolved in it and it doesn’t change temperature rapidly as the H bonds absorb a lot of energy)
How does hydrogen bonding occur between water molecules?
A molecule of water is one atom of O joined by 2 atoms of H by shared electrons. So, the shared negative H electrons are pulled towards the O atom, the other side of each hydrogen atom is left with a slight positive charge. The unshared negative electrons on the O atom give is a slight negative charge. Making water a polar molecule. The slightly negative and positively charged atoms of other water molecules interact with each other causing attraction which is called hydrogen bonding.
How is water less dense as a solid than a liquid?
Water molecules are held further apart in ice than they are in liquid water because each water molecule forms 4 hydrogen bonds to other water molecules, making a lattice shape. This makes ice less dense than water. This is also why ice floats.
What is the Biomolecule name for:
- Carbohydrates
- Lipids
- Proteins
- Nucleic acids
- Carbohydrates = C, H, O
- Lipids = C, H, O
- Proteins = C, H, O, N, S
- Nucleic acids = C, H, O, N, P
What is a condensation reaction?
A reaction in which two molecules join together by a chemical bond with the release of a water molecule. E.g. when two glucose molecules bond together.
What is a hydrolysis reaction?
Hydrolysis is the opposite of a condensation reaction and is when water is added to break a chemical bond between two molecules.
Name of bonds in carbohydrates:
Glycosidic bonds
What are the two forms (isomers) of glucose and how are they different?
The two isomers of the monosaccharide are a-glucose (alpha) and b-glucose (beta). In a-glucose both hydroxyl groups are below their respective H groups. In b-glucose one hydroxyl group is above the H group and one stays below.
Examples of disaccharides and how they are formed:
- Maltose is formed by condensation of two glucose molecules
- Sucrose is formed by condensation of glucose and fructose
- Lactose is formed by condensation of glucose and galactose
What are polysaccharides?
They are macromolecules consisting of more than 2 sugars - often a long chain polymer - joined by glycosidic bonds. They are not sugars.
Examples of polysaccharides and how they are formed?
- Glycogen is formed by the condensation of alpha glucose molecules.
- Starch is formed by the condensation of alpha glucose molecules.
- Cellulose is formed by the condensation of beta glucose molecules.
The chains formed from polysaccharides may be:
- Branched or unbranched
- Folded (making the molecule compact which is ideal for storage e.g. starch and glycogen).
- Straight (making the molecules suitable to construct cellular structures e.g. cellulose) or coiled.
What is the structure and function of Glycogen?
- It’s the main energy storage molecule in animals.
- It’s a multi-branched alpha glucose polymer - joined by 1,4 and 1,6 glycosidic bonds.
- Large number of branches (so energy can be released quickly as enzymes can act simultaneously on these branches).
- Is stored in the muscles and liver
- In times of high energy usage the muscles and liver hydrolyse the glycogen stored and break it down to glucose molecules which can be used in respiration.
- Relatively large but compact molecule which maximises the amount of energy it can store.
- It’s insoluble so it doesn’t affect the water potential of cells and can’t diffuse out of cells.
What is starch?
It’s a mixture of two polysaccharides called amylose and amylopectin. Both amylose and amylopectin are long-chain a-glucose polymers. Starch is the main form of carbohydrate used for energy storage in plants. Starch grains are stored in chloroplasts and are insoluble in water so they don’t affect water potential up and down the xylem - important for water and nutrient transport in the plant.
Structure of Starch:
It consists of two different polysaccharides:
Amylose (10-30%) - Unbranched helix-shaped chain with 1,4 glycosidic bonds between a-glucose molecules. The helix shape enables it to be more compact and thus it’s more resistant to digestion.
Amylopectin (70-90%) - 1,4 glycosidic bonds between a-glucose molecules but also 1,6 glycosidic bonds form between glucose molecules creating a branched molecule.
Properties of amylose:
Branches - Long, unbranched chains
Bonding - 1,4 glycosidic bonds
Shape - Chains coil into a helical shape
Properties of amylopectin:
Branches - Shorter chains, branched
Bonding - 1,4 and 1,6 glycosidic bonds
Shape - Branches out
What is cellulose?
Cellulose is a polysaccharide found in plants. It consists of long chains of b-glucose joined together by 1,4 glycosidic bonds. B-glucose is an isomer of a-glucose, so in order to form the 1,4 glycosidic bonds consecutive B-glucose molecules must be rotated 180 degrees to each other.
Structure and function of cellulose:
- Highly abundant in cell walls, making it one of the most common molecule on Earth.
- Unbranched, linear chains of b-glucose molecules which are joined by glycosidic bonds in a condensation reaction.
- Polymer of about 10,000 b-glucose molecules in a long unbranched chain called a microfibril.
- Microfibrils are strong threads which are made of long cellulose chains running parallel to one another that are joined together by hydrogen bonds forming strong cross linkages.
- High stability due to the structure.
- Adjacent glucose units are in opposite direction.
- It’s important in stopping cell wall from bursting under osmotic pressure. This is as it exerts inward pressure that stops the influx of water, meaning, the cells stay turgid and rigid, helping to maximise the SA of plants for photosynthesis.
What is the test for reducing sugars?
- Label 4 boiling tubes and place 4cm3 of the corresponding samples into each using fresh syringe each time.
- Add 2cm3 of Benedict’s to each sample
- Record the observations of each sample immediately
- Place all 4 boiling tubes into the water bath
- After 2 minutes record your observations of each sample, putting back the samples in the water bath after.
- After another 2 minutes remove the tubes from the water and record final observations.
- If the sample is a reddish colour it contains reducing sugars, if not it will be a blueish colour.
What is the test for non-reducing sugars?
- After carrying out the reducing sugars test, use the negative samples
- Put 4cm3 of each sample into a new test tube and add 2cm3 of 2moldm-3 hydrochloric acid to each of the samples.
- Place all test tubes into the water bath and incubate for 2mins then take them out and let them cool.
- Next neutralise the acid by adding sodium hydrogen carbonate to each sample until no more effervescence is observed.
- Check the pH with indicator paper. If the pH is still lower than pH7, repeat the last step.
- Add 2cm3 of Benedict’s to each of the samples
- Record the observations immediately after and place all boiling tubes into the water bath.
- After 2 mins, record your observations and after another 2 mins remove them from the water and record your final observations.
- If non-reducing sugars are present the solution will turn reddish-brown and if it turns blueish then they aren’t present.
‘A red precipitate shows that a reducing sugar is present, with NO indication of the exact amount’ does this show a semi-quantitative, qualitative or quantitative method?
Qualitative
‘If you weighed the amount of copper oxide precipitate then this would give you a numerical value for the amount’ does this show a semi-quantitative, qualitative or quantitative method?
Quantitative
‘The more colour changes seen on heating with Benedict’s, the more sugar can be estimated to be in the sample being tested’ does this show a semi-quantitative, qualitative or quantitative method?
Semi-quantitative
Properties of lipids:
- They contain carbon, hydrogen and oxygen
- The proportion of carbon to oxygen and hydrogen is smaller than in carbohydrates
- They are insoluble in water
- They are soluble in organic solvents like alcohols, acetone and hexane
Function of lipids: (HINT: SHIPS)
- Storage of energy for long-term use (e.g. triglycerides)
- Hormonal roles (e.g. steroids such as oestrogen and testosterone)
- Insulation - both thermal (triglycerides) and electrical (sphingolipids)
- Protection of internal organs (triglycerides and waxes)
- Structural components of cells (phospholipids and cholesterol)
What are the main lipid types?
- Triglycerides and phospholipids
How are triglycerides formed with an explanation?
When condensation reactions occur between one glycerol and three fatty acid chains they are formed.
The hydroxyl groups of glycerol combine with the carboxyl groups of the fatty acids to form an ester linkage. This condensation reaction results in the formation of three molecules of water. During breakdown, these ester bonds are broken down by hydrolysis.
This also means when one triglyceride forms, three water molecules are released.
Describe saturated fatty acids:
These are fatty acids that possess no double bonds. This generates fats that are usually solid at room temperature. Saturated fatty acids are linear in structure, originate from animal sources and are typically solid at room temperatures.
Describe unsaturated fatty acids:
Fatty acids with noble bonds are unsaturated - either monounsaturated or polyunsaturated (>1 double bond). Unsaturated fatty acids are bent in structure, originate from plant sources (i.e. oils). Unsaturated fatty acids are usually liquid at room temperature and are called oils.
Describe the structure of a phospholipid:
In its hydrophilic head contains the phosphate group and the phosphoester bond. In the hydrophobic tail, the phosphoester bond connects to the glycerol. The glycerol forms ester bonds with the fatty acids. As phospholipids have both hydrophobic and hydrophilic parts they are amphipathic. Due to this, phospholipid molecules form monolayers or bilayers in water.
Describe the function of phospholipids:
- Forming the plasma membrane of cells
- In an aqueous environment being polar means a bilayer can be formed
- The form the bilayer with the FA tails facing each other and the polar heads facing outwards.
- Their structure allows them to form glycolipids with carbohydrates which are important on the cell surface membrane for cell recognition.
- They are ideal for forming cell surface membranes as they enable integration of other molecules into the ‘mosaic’ and help regulate the movement of molecules in and out of the cell.
Describe the function and structure of cholesterol:
Cholesterol is manufactured primarily in the liver and intestines. It has a 4 carbon ring structure with a hydroxyl group at one end. Cholesterol is important in the formation and fluidity of cell surface membranes and in the production of certain hormones e.g. testosterone.
(Sterols (steroid alcohols) are another type of lipid found in cells)
Describe Low density lipoproteins (LDLs) and how they form:
Triglycerides (from fats sin our diet) combine with cholesterol and proteins to form LDLs which transport the cholesterol to our body cells.
LDLs carry cholesterol from the liver to the rest of the body. LDLs bind to receptors on cell surface membranes before being taken up by the cells where the cholesterol is involved in maintenance and synthesis of cell membranes. Excess LDL overload on these membrane receptors, results in high blood cholesterol levels, which can be deposited in the artery walls forming atheromas.
Describe High density lipoproteins (HDLs) and how they form:
HDLs are formed when triglycerides combine with proteins and cholesterol. They have a higher density because they have higher percentage of proteins and less cholesterol compared to LDLs. HDLs scavenge excess cholesterol in the body tissues and carry it back to the liver where it’s broken down which lowers blood cholesterol levels, and helps to remove the fatty plaques of atherosclerosis.
(think of ‘H’ for hoover - so they hoover the excess cholesterol in the arteries and carries to the liver where its broken down and passed through the body. So, LDLs raise blood cholesterol levels and HDLs lower blood cholesterol levels).
Why is it admirable to maintain a higher HDL:LDL ratio in the blood?
LDLs can form atherosclerotic plaques in the arteries whereas HDLs reduce blood cholesterol deposition. So, having higher HDL promotes excretion.
