2.2 - Biological Molecules Flashcards
What is a covalent bond?
The sharing of electron pairs between atoms.
How does a Condensation reaction occur?
When two molecules are joined together with the removal of water.
How does a Hydrolysis reaction occur?
When ma molecule is split into two smaller molecules with the addition of water.
What is a monomer?
A small molecule which binds to many other identical molecules to form a polymer.
What is a polymer?
A large molecule made from many smaller molecules called monomers.
State the 3 main biological molecules studied in this chapter, along with the elements found in those molecules, and its respective monomer and polymer.
Carbohydrates - C, H, O - Monosaccharides - Polysaccharides
Proteins - C, H, O, N, S - Amino acids - Polypeptides and proteins
Nucleic acids - C, H, O, N, P - Nucleotides - DNA and RNA
What are hydrogen bonds and how do they occur?
A weak interaction that can occur wherever molecules contain a slightly negatively charged atom bonded to a slightly positively charged hydrogen atom.
What are the 7 properties of water?
- Liquid
- Density
- Solvent
- Cohesion and surface tension
- High specific heat capacity
- High latent heat of vaporisation
- Reactant
Explain why water is a liquid at room temperature.
The hydrogen bonds between water molecules make it more difficult for them to escape to become a gas.
State 4 benefits of water being a liquid.
- Provides habitats for aquatic organisms.
- Forms a major component of the tissue in living organisms.
- Provides a reaction medium for chemical reaction.
- Provides an effective transport medium, e.g. in blood and vascular tissue.
Explain why ice is less dense than water.
Water becomes more dense as it gets colder until about 4 C. From 4 C to freezing point, due to its polar structure, the water molecules align themselves in a structure which is less dense than liquid water (open lattice).
State 2 benefits of ice being less dense than a water.
- Aquatic organisms have a stable environment in which to live through the winter.
- Ponds and other bodies of water are insulated against extreme cold. The layer of ice reduces the rate of heat loss from the rest of the pond.
Explain how water is a good solvent for many substances found in living things.
Because water is polar, the positive and negative parts of the water molecules are attracted to the negative and positive parts of the solute.
The water molecules cluster around these charged parts of the solute molecules/ions, and will help to separate them and keep them apart. They are then dissolved so a solution is formed.
State 2 benefits of water being a good solvent.
- Molecules and ions can move around and react together in water.
- Molecules and ions can be transported around living things whilst dissolved in water.
Explain how cohesion and surface tension in terms of water works.
Cohesion - where the hydrogen bonding between the water molecules pull them together (e.g. a drop of water on a flat surface is spherical)
Surface tension - where the water molecules at the surface are all hydrogen-bonded to the molecules beneath them, and hence more attracted to the water molecules beneath than to the air molecules above. Thus, the surface of the water contracts and it gives the surface of the water an ability to resist force applied to it.
State 2 benefits of cohesion and surface tension.
- Columns of water in plant vascular tissue are pulled up the xylem tissue together from the roots.
- Insects like pond-skaters can walk on water.
Explain why water has a high specific heat capacity.
Water molecules are held together tightly by hydrogen bonds. A lot of heat is energy is required to increase their kinetic energy and temperature. This means that water does not heat up or cool down easily.
The specific heat capacity of energy to raise the temperature of 1 kg of water by 1 C is 4.2 kJ.
State 2 benefits of water having a high specific heat capacity.
- Living things, e.g. prokaryotes/eukaryotes, need a stable temperature for enzyme-controlled reactions to happen properly.
- Aquatic organisms need a stable environment in which to live.
Explain why water has a high latent heat of vaporisation.
The molecules are held together quite tightly by hydrogen bonds so a relatively large amount of energy is needed for water molecules to evaporate.
State 1 benefit of water having a high latent heat of vaporisation.
- Helps cool living things and keep their temperature stable (e.g. mammals cooled when sweat evaporates and plants cooled when water evaporates from mesophyll cells).
What is the general formula for carbohydrates?
C n H 2n O n
What are the three main functions of carbohydrates?
- A source of energy (e.g. glucose)
- A store of energy (e.g. starch/glycogen)
- Structural units (e.g. cellulose in plants and chitin in insects)
What are monosaccharides? What are they particularly important in? Why are they well suited to this role?
The simplest carbohydrates (monomers). They are particularly important in living things as a SOURCE of energy. They are well suited to this role because of the large number of C-H bonds.
Describe how monosaccharides taste like and their solubility.
They are sugars so they taste sweet.
They are soluble in water but insoluble in non-polar solvents.
What are three forms that monosaccharides can exist as?
Straight chained, ring, cyclic.
What do monosaccharides have a backbone of? What is the name of the group formed?
Single-bonded carbon atoms with one double-bonded to an oxygen atom to form a CARBONYL group.
What do monosaccharides join to make?
Disaccharides or polysaccharides.
In solution, triose and tetrose sugars exist as ……..
Pentoses and hexoses are more likely to be found as……
In solution, triose and tetrose sugars exist as straight chains.
Pentoses and hexoses are more likely to be found as a ring or cyclic form.
Glucose can exist as isomers. What are isomers?
Molecules with the same formula but whose atoms are arranged differently in space.
How are disaccharides made?
When two monosaccharides join together.
State what is named when the following monosaccharides are joined together: a-glucose + a-glucose = ....... a-glucose + fructose =....... b-glucose + a-glucose = ...... b-glucose + b-glucose = ......
a-glucose + a-glucose = MALTOSE
a-glucose + fructose = SUCROSE
b-glucose + a-glucose = LACTOSE
b-glucose + b-glucose = CELLOBIOSE
When monosaccharides join together, what is formed?
A CONDENSATION REACTION occurs to form a GLYCOSIDIC BOND.
Explain how a glycosidic bond is formed when monosaccharides join together.
Two hydroxyl groups line up next to each other, from which a water molecule is removed. This leaves an oxygen atom acting as a link between the two monosaccharide units.
How are disaccharides broken into monosaccharides?
By a HYDROLYSIS REACTION, which requires the ADDITION OF WATER. The water provides a hydroxyl group (-OH) and a hydrogen (H) which help the glycosidic bond to break.
What is the molecular formula of glucose (both alpha and beta)?
C6H12O6
What is the role of a-glucose in the body?
Energy SOURCE. COMPONENT of starch and glycogen, which act as energy STORES.
What is the role of b-glucose in the body?
Energy SOURCE. COMPONENT of cellulose, which provides structural support in plant cell walls.
What is the molecular formula of Ribose?
C5 H10 O5
What is the role of ribose in the body?
COMPONENT of ribonucleic acid (RNA), ATP and NAD.
What is the molecular formula of Deoxyribose?
C5 H10 O4 (one less oxygen atom than ribose, hence DEoxyribose)
What is the role of deoxyribose in the body?
COMPONENT of deoxyribonucleic acid (DNA).
What type of sugar is both alpha and beta glucose?
What type of sugar is both ribose and deoxyribose?
Alpha and Beta Glucose: HEXOSE
Ribose and Deoxyribose: PENTOSE
What are polysaccharides?
POLYMERS of MONOSACCHARIDES.
What are homopolysaccharides? Give one example.
Polysaccharides made solely of one kind of monosaccharide.
Example: STARCH
What are heteropolysaccharides?
Polysaccharides made of more than one monosaccharide.
Example: HYALURONIC ACID
If you join lots of glucose molecules together into polysaccharides, what can you create?
A STORE of energy.
How do plants store energy?
Plants store energy as STARCH (amylose and amylopectin) in CHLOROPLASTS.
Humans store energy as GLYCOGEN in cells of the muscle and liver.
Give 4 reasons why polysaccharides form good stores of monosaccharides.
- Glycogen and starch are compact so they do not occupy a large amount of space.
- Polysaccharides hold glucose molecules in chains so they can be easily ‘snipped off’ from the end of the chain by hydrolysis when required for respiration.
- Branched chains, such as amylopectin, tend to be more compact. They also offer the chance for LOTS of glucose molecules to be snipped off by hydrolysis at the SAME TIME, when lots of energy is required QUICKLY.
- Polysaccharides are less soluble in water than monosaccharides. If many glucose molecules did dissolve in the cytoplasm, the water potential would reduce and excess water would diffuse in. They are less soluble because not only of their size but because regions which could hydrogen-bond with water are hidden away inside the molecule.
What is Amylose?
It’s a type of starch in plants. It is a long chain of a-glucose molecules. Like maltose, it has glycosidic bonds between carbons 1-4.
Describe the structure of amylose. Explain its properties due to its structure.
Amylose coils into a spiral shape with hydrogen bonds holding the spiral in place. Hydroxyl groups on Carbon-2 are situated on the inside of the coil, making the molecule less soluble and allowing hydrogen’s bonds to form to maintain the coil’s structure.
What is Amylopectin?
It’s a type of starch in plants. It is similar to amylose in that it has glycosidic bonds between carbon 1-4 but it also has BRANCHES formed by glycosidic bonds between carbon 1-6.
Describe the structure of amylopectin.
Amylopectin also coils into a spiral shape, held together with hydrogen-bonds but with branches emerging from the spiral.
What is Glycogen?
It is like amylopectin with glycosidic bonds between carbon 1-4 with branches formed by glycosidic bonds between carbon 1-6.
Describe the structure of glycogen. (Hint: compare it with amylopectin).
The 1-4 bonded chains tend to be smaller than in amylopectin, so glycogen has LESS TENDENCY TO COIL. However, it has MORE BRANCHES which makes it more compact. It is also easier to remove monomer units as there are more ends.
