Biological Molecules Flashcards
What are the characteristics of water that pertain to its biological role and what causes these characteristics?
- High boiling-point, specific heat capacity and thermal stability caused by strong hydrogen bonding network
- High surface tension caused by hydrogen bonding network
- Water can act as a solvent for polar or charged substances as a result of its polarity
- Less dense in solid form than liquid form; this is caused by the rigid and open tetrahedral network of water molecules formed when water freezes
- Water has cohesive (sticking to itself) and adhesive (sticking to other materials) properties due to its polarity causing it to form intermolecular bonds with itself and other polar substances
What biological roles do water’s characteristics allow it to perform?
- Main constituent of cytosol - Its ability to act as a solvent means substances can dissolve within the cytosol and react with one another.
- Transport medium - Its ability to act as a solvent and its ability to travel via capillary action mean dissolved substances can readily travel within it around organisms. This is observed in mammalian blood vessels and in xylem.
- Coolant and thermal regulator - Its high specific heat capacity allows it to provide thermal stability to the surrounding environment, which is essential for enzyme function. This occurs within and outside organisms.
- Main constituent of certain habitats - Its thermal stability provides a constant temperature for aquatic organisms. Its high surface tension allows certain organisms, e.g. pond skaters to live on it. Ice’s lower density means an insulating layer forms on top of bodies of water at low temperatures, allowing aquatic live to thrive beneath it.
What are the chemical elements that make up the biological molecules carbohydrates, lipids, proteins and nucleic acids?
- Carbohydrates - carbon, hydrogen and oxygen
- Proteins - carbon, hydrogen, oxygen, nitrogen and sometimes sulfur
- Lipids - carbon, hydrogen, oxygen
- Nucleic acids - carbon, hydrogen, oxygen, nitrogen and phosphorus
Lipids can contain elements such as phosphorus, nitrogen and sulfur, but for the sake of this qualification, assume they only contain carbon, hydrogen and oxygen (unless phospholipids are clearly involved)
What is the structure of alpha-glucose?
What is the structure of beta-glucose?
As both types of glucose monomers have six carbons, it is referred to as a hexose monosaccharide
What is the structure of ribose?
As ribose has five carbons, it is referred to as a pentose monosaccharide
What are the properties of glucose?
- Small
- Polar
- Soluble in polar solvents like water
These properties extend to all monosaccharides
How are polysaccharides formed?
General explanation
- Polymerisation reaction involving monosaccharides as monomers
- The reaction is a condensation reaction as a molecule of water is produced with the formation of every bond
- The same processes occur in the dimerisation reaction to form disaccharides from monosaccharides
- Disaccharides can react with one another or with monosaccharides to form polysaccharides
How exactly is a maltose molecule formed and what is the bond that forms called?
- Two alpha glucose molecules react
- The hydroxyl group on carbon one of a glucose molecule and the hydrogen on the hydroxyl group on carbon four of another glucose molecule are cleaved, releasing a molecule of water
- A bond forms between the carbon one and the oxygen on the carbon four
- The bond formed is called a 1,4 glycosidic bond
It is possible for the whole hydroxyl group to break from carbon four and only hydrogen to break from carbon one instead
How are polysaccharides broken apart?
- One or more molecules of water are introduced
- A molecule of water will react with a glycosidic bond, reforming both hydroxyl groups and cleaving the two monomers
- This process is known as hydrolysis, and consumes water
What monosaccharides do the disaccharides maltose, sucrose and lactose consist of?
- Maltose - two glucose molecules
- Sucrose - a glucose and a fructose molecule
- Lactose - a glucose and a galactose molecule
Fructose and galactose are hexose monosaccharides
What are the two types of starch?
- Amylose - makes up around 20% of natural starch
- Amylopectin - makes up around 80% of natural starch
What is the structure of amylose?
- Consists of alpha glucose molecules joined together by 1,4 glycosidic bonds, forming a linear, unbranched chain
- The angle of these bonds causes the chain to twist, forming a helix stabilised by internal hydrogen bonding
What is the structure of amylopectin?
- Amylopectin also consists of glucose molecules joined by 1,4 glycosidic bonds that form linear chains
- However, approximately every 25 glucose molecules (subunits), two glucose molecules will be joined by a 1,6 glycosidic bond
- This gives amylopectin a branched structure with many linear chains
- Each individual chain of amylopectin is able to coil
- A 1,6 glycosidic bond involves bonding between carbon one on one glucose monomer and carbon six on another; everything else is the same
What is the structure of glycogen?
- It has the same structure as amylopectin, except it has 1,6 glycosidic bonds every 10 subunits instead of every 25 subunits
- This provides it with a highly branched structure
Each individual chain of glycogen is able to coil
What is the structure of cellulose?
- Cellulose consists of chains of beta glucose molecules, with every other beta glucose molecules being flipped upsidedown to allow the hydroxyl groups to interact
- There is no coiling or branching - it is just a straight, linear chain
- These chains form hydrogen bonds between one another, forming microfibrils
- These microfibrils combine to make macrofibrils, which combine to form cellulose fibres
What are the properties of amylose, and how do these properties link to its function?
- It is very compact
- It is insoluble and unreactive (not readily reduced or digested)
- These properties allow it to store a large amount of glucose (which is used as energy) in a small area while not reacting or dissolving
What are the properties of amylopectin, and how do these properties link to its function?
- Its many terminal ends make it able to readily release and accept glucose molecules
- This is optimal for respiration and energy storage on demand in plants
- It is mostly insoluble, though a little more soluble than amylose, so it can be stored without dissolving
- Its branched structure means it has many glucose monomers per grain, though a single molecule of amylopectin is less compact than a molecule of amylose
- Overall, it is very compact, which is an ideal characteristic for an energy storage molecule
What are the properties of glycogen, and how do these properties link to its function?
- Its many terminal ends make it able to readily release or accept, facilitating the rapid respiration and energy storage animals require for movement
- Its branching makes it more compact than both types of starch; this is essential for animals that move around
- It is insoluble, so can be stored without dissolving
What are the properties of cellulose, and how do these properties link to its function?
- High tensile strength (ability to resist breaking under tension) due to covalent and hydrogen bonding
- Permeable
- Very insoluble and difficult to break down (indigestible)
- These properties make it suitable for plant cell walls, as it means cell walls can maintain the rigidity of cells, withstand turgor pressure and allow substances through without being dissolved
What is the difference between fats and oils?
- Fats are lipids that are solid at room temperature
- Oils are lipids that are liquid at room temperature
There are some lipids that are not fats or oils, however
What is the structure of fatty acids?
- They are carboxylic acids with long hydrocarbon chains
- They can be saturated (no double bonds) or unsaturated (double bonds)
- A fatty acid with one double bond is monounsaturated, while one with multiple is polyunsaturated
- The hydrocarbon chain can have heteroatoms attached to it
- Cis-trans isomerism is exhibited across the double bond(s), resulting in what we call ‘trans-fats’
- Double bonds lead to kinks, reducing the ability for unsaturated lipids to pack closely together, making them more likely to be oils
What is the structure of glycerol?
- Glyercol is a type of alcohol called a triol (three hydroxyl groups)
- It consists of three carbons, each with a hydroxyl group bonded to them
What is the structure of a triglyceride and what are its properties?
- Three fatty acids bonded to glycerol
- It is considered a macromolecule in its own right, though it is not a polymer
- It is non-polar due to the long fatty acid chains; the head is slightly polar but this is not enough to counteract the non-polarity of the fatty acids or to make the head hydrophilic
- This makes it highly insoluble in water and hydrophobic
- It is soluble in non-polar solvents, or solvents that are mostly non-polar like ethanol
Glycerol is polar when isolated, but its polarity is muted after the hydroxyl groups are removed