Biological Molecules Flashcards
What makes water a polar molecule?
The shared negative hydrogen electrons are pulled towards the oxygen atom, so the other side of each hydrogen atom gets a slight positive charge. The unshared negative electrons on the oxygen atom give it a slight negative charge. This makes water a polar molecule as it has partial charges on each side.
What are hydrogen bonds?
Hydrogen bonds are weak bonds between a slightly positively charged hydrogen atom in one molecule and a slightly negatively charged atom in another molecule (usually oxygen).
What type of bonds form between water molecules?
Hydrogen bonds
Why do water molecules form hydrogen bonds between them?
The slightly negatively charged oxygen atoms of water attract the slightly positively charged hydrogen atoms of other water molecules.
What are the key properties of water?
- important metabolite
- good solvent
- large latent heat of vaporisation
- high specific heat capacity
- very cohesive
- high surface tension
- transparent
How does water contribute to metabolic reactions?
Many metabolic reactions involve condensation or hydrolysis reactions. Hydrolysis reactions require a molecule of water to break a bond. Condensation reactions release a molecule of water for every bond they form.
Why can water be described as a metabolite?
Water is a metabolite because it is a substance which is involved in metabolic reactions (chemical reactions which occur in living organisms to keep the organism alive).
Why is water a good solvent?
Because water is polar, the slightly positively charged end of the molecule is attracted to a negative ion and vice versa. This means that ions get completely surrounded by water molecules, so they will dissolve.
Why is it important that water is a good solvent?
Many metabolic reactions take place in solution (e.g. in the cytoplasm of cells), so water is important to allow this. Water also dissolves mineral ions and other substances to be transported in the blood plasma or around a plant.
Why does water have a large latent heat of vaporisation?
Water can only evaporate when the hydrogen bonds between molecules are broken. It takes a lot of energy to break the hydrogen bonds, so it takes lots of energy to change the state of 1g of water. This means that water has a large latent heat of vaporisation.
Why is water’s large latent heat of vaporisation useful for organisms?
They can use water loss through evaporation to cool down without using too much water. When water evaporates it carries away heat energy from a surface, which cools down the surface and helps to lower the temperature (e.g. sweating in humans).
What is specific heat capacity?
The amount of energy needed to raise the temperature of 1g of a substance by 1 degrees C.
Why does water have a high specific heat capacity?
It takes lots of energy to break the hydrogen bonds between water molecules, so there is less energy remaining to heat the water. It therefore takes lots of energy to heat up water.
Why is it important that water has a high specific heat capacity?
Water’s high specific heat capacity means it can buffer (resist) changes in temperature. Because so much energy is needed to heat water, large bodies of water, like lakes, ponds or oceans, have a fairly stable temperature which rarely changes more than a few degrees, even if the air temperature is changing rapidly. This produces a stable environment for marine life. This is significant in organisms which use enzyme-controlled reactions, as these are heavily affected by temperature.
Why is water very cohesive?
Water molecules a cohesive because they are polar. The slightly positively charged hydrogen atoms are attracted to the slightly negatively charged oxygen atoms of other water molecules. This causes water to ‘stick’ together and flow.
What is cohesion?
Cohesion is the attraction between molecules of the same type.
What is the importance of water’s strong cohesion?
It allows water to travel in columns, for example, through the xylem vessels of plants. It is key that water can move through the xylem vessels as it is needed for photosynthesis. Water’s cohesion also means that it has high surface tension. This allows pond skaters to move across the surface of a lake without drowning.
What causes water’s high surface tension?
The water molecules are more attracted to each other than they are to the air around them, meaning objects can float on the surface of water without falling in.
Why is it important that water is transparent?
The fact that water is transparent means that light can get to plants beneath the surface of ponds. This is crucial to these plants’ survival as they need light to carry out photosynthesis.
What is an inorganic ion?
An atom or group of atoms with an electric charge which does not contain carbon.
Where are inorganic ions found in the body?
Inorganic ions occur in solution in the cytoplasm and body fluids of organisms, some in high concentrations and others in very low concentrations.
What determines an ion’s role?
Each type of ion has a specific role, depending on its properties. An ion’s role determines whether it is in high or low concentrations.
What is the role of iron ions in the body?
Iron ions are found in the Haemoglobin of red blood cells (Haemoglobin is a large protein that carries oxygen around the body, in RBC). Haemoglobin is made up of four polypeptide chains, each with an iron ion (Fe2+) in the centre. The Fe2+ ion binds to the oxygen in Haemoglobin. When the oxygen is bound, the Fe2+ ion becomes an Fe3+ ion, until the oxygen is released.
What is the role of hydrogen ions?
The concentration of H+ ions determines the pH of an environment. The more H+ present, the lower the pH. Enzyme-controlled reactions are affected by pH. H+ ions are also involved in the buffering of solutions.
What is the role of sodium ions?
Glucose and amino acids can’t travel across cell membranes on their own. A molecule of glucose or an amino acid can be transported into a cell alongside sodium ions (co-transport).
What is the role of phosphate ions?
When a phosphate ion is attached to another molecule, it’s known as a phosphate group. DNA, RNA, and ATP all contain phosphate groups. The bonds between phosphate groups in ATP store energy. The phosphate groups in DNA and RNA allow nucleotides to join up to form polynucleotides. Phosphate ions are involved in the synthesis of ATP and the production of phospholipids.
What is the role of calcium ions?
Calcium ions are involved in the ossification of bones and teeth. They are also involved in synaptic transmission (the release of the neurotransmitter across the synaptic cleft).
What is the role of magnesium ions?
Magnesium is a major component of chlorophyll, so without magnesium ions, plants wouldn’t be able to photosynthesise.
What are monosaccharides?
The monomers from which larger carbohydrates are made.
What are disaccharides?
Disaccharides are formed by the condensation of two monosaccharides.
What type of bond is formed by the condensation of two monosaccharides?
Glycosidic bond
How is maltose formed?
By the condensation of two glucose molecules
How is sucrose formed?
By the condensation of a glucose molecule and a fructose molecule.
How is lactose formed?
By the condensation of a glucose molecule and a galactose molecule.
What type of sugar is sucrose?
Non-reducing sugar
What type of sugar are maltose and lactose?
Reducing sugars
What is an isomer?
Isomers are chemical compounds which have the same chemical formula but a different structural formula.
What are the two isomers of glucose?
Alpha and beta glucose
What is the difference between alpha and beta glucose?
In alpha glucose, the hydrogen on C1 is above C1 and the hydroxide is below C1. Whereas, in beta glucose, the hydrogen on C1 is below C1 and the hydroxide is above C1.
Describe the structure of glucose.
- 6 carbon atoms in a hexagonal ring
- the vertex of the hexagon between C1 and C5 is an oxygen atom
- the sixth carbon atom is bonded to the 5th carbon atom
- for C1, H above, OH below (beta glucose is opposite)
- for C2, H above, OH below
- for C3, OH above, H below
- for C4, H above, OH below
- for C5, CH2OH above, H below
How do you draw the simplified form of the glucose molecule?
You do not need to draw any of the hydrogen or carbon atoms on C2, C3, C5 or C6. You do need to draw the oxygen atom between C5 and C1 and the hydrogen and hydroxide ions on C1 and C4.
What type of bond is formed when two glucose molecules condense into a maltose molecule?
1 to 4 alpha glycosidic bond
What is the test for reducing sugars?
Add Benedict’s solution to the solution you are testing. Place in a heated water bath. If reducing sugars (monosaccharides and some disaccharides) are present, then a coloured precipitate will form (green, yellow, orange or brick red depending on amount of reducing sugar). If the solution remains blue, there is no reducing sugars.
How do you test for non-reducing sugars?
Heat a sample of the solution you are testing with dilute hydrochloric acid (breaks glycosidic bonds) in a water bath. Neutralise it with sodium hydrogencarbonate. Add Benedict’s solution and warm in a water bath. If the colour changes from blue to green/yellow/orange/brick red, non-reducing sugars are present.
What are polysaccharides?
Polysaccharides are large polymers of saccharides formed by the linkage of many (over 10) monosaccharides.
How are polysaccharides formed?
Polysaccharides are formed by the condensation of many glucose units.
What are the properties of polysaccharides?
Insoluble/colloidal, osmotically inactive, not sweet tasting, may be linear or branched
What are the functions of polysaccharides?
The specific function depends on which polysaccharide it is, but generally, polysaccharides are used for energy storage or for structural functions.
What are the properties of disaccharides?
Sweet tasting, soluble in water, osmotically active
What is the function of sucrose?
Energy transport and storage in plants
What is the function of lactose?
Energy transport and storage in mammal milk
What is the function of maltose?
Intermediate in starch digestion
What is the monomer for starch?
Alpha glucose
What are the two polysaccharides which make up starch?
- amylose
- amylopectin
What is the structure of amylose?
Amylose is a long, unbranched chain of alpha glucose. It is coiled into a helix and is very compact.
Why is amylose unbranched?
Amylose is unbranched because it only contains 1-4 alpha glycosidic bonds, so forms one long chain. There are no 1-6 alpha glycosidic bonds, so branches can’t form.
Why does amylose form a helix?
Amylose forms a helix because the angles of the glycosidic bonds make it coiled. There is also hydrogen bonding between glucose molecules, which makes it compact and coiled.
What is the structure of amylopectin?
Amylopectin is a long, branched chain of alpha glucose.
What is the importance of amylopectin being branched?
The side branches allow the enzymes that break down amylopectin to get to the glycosidic bonds easily. This means that the glucose can be released quickly, which means energy can be released through respiration.
What allows amylopectin to be branched?
Amylopectin has both 1-4 alpha glycosidic bonds, which hold together the molecules in the main chain, but also 1-6 alpha glycosidic bonds, which connect branch chains to the main chain. This allows for branching.
Where is starch stored?
Starch is only stored in plants, not in animals.
Why is starch good for storage?
Starch is insoluble in water and doesn’t affect water potential, so it doesn’t cause water to enter cells by osmosis, which would make them swell. Therefore, starch is good for storage. Starch also has a helical structure, so is compact, meaning lots of it can fit in a small space. Starch is a large molecule, so cannot leave cells.
What is the monomer for glycogen?
Alpha glucose
What is the function of starch?
Starch is used to store excess glucose in plants. When plants need energy, they hydrolyse starch to release glucose for respiration, releasing energy.
What is the function of glycogen?
Glycogen acts as an energy store in animals (excess glucose is stored as glycogen). This energy can be released when glycogen is broken down into glucose and used in respiration.
What is the structure of glycogen?
Glycogen is a long chain of alpha glucose molecules, with many branches. Glycogen is a compact molecule.
Why is it important that glycogen is very branched?
The fact that there is lots of branching in glycogen means that hydrolysis reactions can happen more quickly to break down the glycogen into starch (as enzymes can reach the glycosidic bonds more easily). This means that energy can be released from glycogen quickly as the glucose released is used in respiration.
Why is glycogen more branched than amylopectin?
The more branched the polysaccharides are, the more quickly their stored energy can be released. Since animals are more metabolically active than plants, glycogen is more branched than amylopectin, as glycogen is stored in animals, whereas amylopectin makes up starch, which is stored in plants.
Where is glycogen stored?
Glycogen is stored in animals, not in plants, in the liver and muscle cells
What is the test for starch?
Add the test solution to a test tube then add iodine in potassium iodide solution. If starch is present, the colour will change from brown/orange to black.
