2.1.2 Biological Molecules Flashcards
What is the importance of water?
- Reactant in lots of chemical reactions (incl. hydrolysis)
- Solvent as some substances dissolve in it
- Transports substances like glucose and oxygen around plants and animals
- Temperature control (thermoregulation)
- Habitat for organisms to survive and reproduce in
- Ice floats which forms an insulating layer
How is water polar?
- It is polar due to the unevenly distributed charge
- The oxygen end acts negative
- The hydrogen end acts positive
- Water is polar as it has both positive and negative charge
- Overall, water is neutral
How do hydrogen bonds form?
- Formed between a highly electro-negative atom of a polar molecule and a hydrogen
- One hydrogen bond is weak but many bonds are strong
What is cohesion?
- It produces a surface film on the water (e.g. allowing insects to walk on water surface)
- Attraction between molecules of the same type due to polarity of the molecule
- Results in surface tension
- Water has a greater surface tension than most liquids because hydrogen bonds resist stretching or breaking of the surface
What is adhesion?
- Attraction between two different substances
- Water will make hydrogen bonds with other surfaces (e.g. transpiration process which plants remove water from soil)
What is the specific heat capacity of water?
- Water has a high specific heat capacity
- Water can absorb and release large amounts of heat energy with little change in the actual temperature due to the hydrogen bonds
- Water prevents temperature fluctuations and provides a stable thermal environment
What is the latent heat of vaporisation of water?
- Water has a high latent heat of vaporisation (amount of energy to convert 1kg of water from a liquid to a gas)
- For water to evaporate, hydrogen bonds must be broken
- As water evaporates, it removes a lot of heat with it (cooling effect)
- This moderates Earth’s climate and prevents organisms from overheating
What is the density of water?
- Ice is less dense as a solid than as a liquid
- Liquid water has hydrogen bonds that are constantly being broken and reformed
- Frozen water forms a crystal like lattice where molecules are set at fixed distances
- Prevents water from freezing from the bottom up
- Ice forms on surface first as freezing of water releases heat to the water below, creating insulation
- Makes transition between season less abrupt
How is water a good solvent?
- Water is polar so the positive and negative parts are attracted to the negative and positive parts of a solute
- Water molecules cluster around the the charged parts of the solute molecules and keep them apart so they can dissolve
- As water is a good solvent, molecules and ions can be transported around living things whilst dissolved and reactions can occur
What is a monomer and a polymer?
A monomer is a single unit and a polymer is when many of the same monomers have been joined together
What is a condensation reaction?
A condensation reaction occurs when 2 molecules are joined together with the removal of water
What is a hydrolysis reaction?
A hydrolysis reaction uses water to split molecules apart
What elements, monomers and polymers are in carbohydrates?
Elements - C, H and O
Monomers - monosaccharides (e.g. glucose)
Polymers - polysaccharides (e.g. starch)
What elements, monomers and polymers are in proteins?
Elements - C, H, O, N and S
Monomers - amino acids
Polymers - polypeptides and proteins
What elements, monomers and polymers are in nucleic acids?
Elements - C, H, O, N and P
Monomers - nucleotides
Polymers - DNA and RNA
What elements are in lipids?
C, H and O
What are the uses of carbohydrates?
- Substrate for respiration
- Energy store (starch and glycogen)
- Recognition of molecules outside a cell
- Structure (cellulose and chitin)
- Hereditary information
What is the structure of an alpha and beta glucose ring?
- In an alpha glucose ring, the H is on top of the OH on the first carbon
- In a beta glucose ring, the H is below the OH on the first carbon
What is a disaccharide?
Formed from two monosaccharides joined by a glycosidic bond during a condensation reaction
What are the monomers in different disaccharides?
Glucose + glucose = maltose
Glucose + galactose = lactose
Glucose + fructose = sucrose
What is starch?
- Energy store in plants
- Excess glucose is stored as starch
What is the structure of starch?
- Mixture of amylose and amylopectin
- Amylose is a long unbranched chain of α glucose and has a compact coiled structure
- It is good for storage and has 1-4 glycosidic bonds
- Amylopectin is a long branched chain of α glucose
- It has 1-4 and 1-6 glycosidic bonds
- Glucose can be released quickly as it is easier for enzymes to get to branches (more easily hydrolysed)
What is glycogen?
- Energy store in animals
- Excess glucose is stored as glycogen
- Found in the liver and muscles
What is the structure of glycogen?
- It is a polysaccharide of α glucose
- Lots of side branches for fast release of energy (easily hydrolysed)
- 1-4 and 1-6 glycosidic bonds
What is cellulose?
- Structural support for cells (in cell wall) in plants
What is the structure of cellulose?
- Long straight unbranched chains of β glucose
- Hydrogen bonds between chains forming microfibrils
- 1-4 glycosidic bonds
- Each alternate glucose molecule rotates 180° to allow bonding of hydroxyl groups
- Chains run parallel to each other (microfibrils) and are strengthened with cross-linkages (hydrogen bonds)
- Stability makes it difficult to digest
What are lipids?
Macromolecules (not polymers) as they are made of different components
Insoluble as they aren’t polar
What are triglycerides?
- Macromolecules
- Contain one molecule of glycerol and three fatty acid tails
What are the functions of triglycerides?
- Energy source (secondary respiratory substrate)
- Energy store
- Insulation
- Buoyancy
- Protection
What is the structure of glycerol?
- Made of 3 carbon atoms
- Each has a hydroxyl group attached to it on the right
- Hydrogen atoms occupy remaining positions
What is the structure of fatty acids?
- Contains an acid group (COOH) attached to a hydrocarbon chain
What are the types of fatty acids?
Saturated = every carbon atom is joined by a single C-C bond
Monounsaturated = contains one C=C bond
Polyunsaturated = many double bonds
- Double bonds make the molecule more fluid due to the kink in its structure
What is the process of creating triglyceride molecules?
Esterification as an ester link/bond is formed
What is the structure of phospholipids?
- Contains a diglyceride, a phosphate group and a simple organic molecule (choline)
- One fatty acid tail is substituted
- Most commonly has 1 saturated and 1 unsaturated hydrocarbon chain
What do phospholipids do in water?
- The phosphate group has a negative charge, attracted by water (hydrophillic)
- The fatty acid tails are non polar, repelled by water (hydrophobic)
What is the structure of an amino acid?
It has a central carbon atom with 4 different chemical groups
- Amino group
- Carboxyl group
- H group
- R side chain
How many different amino acids are there?
- 20 as there are 20 different R groups
- Glycine is the basic amino acid structure
How is a peptide bond formed?
Condensation reaction
What is the primary structure of a protein?
- The order and sequence of amino acids in a polypeptide chain
- Amino acids are joined together to make a polypeptide in a process called polymerisation
- Primary structure of a protein determines its ultimate shape and function
- Changing the amino acid can lead to changes in the shape of the protein
What is the secondary structure of a protein?
- POlypeptide has -NH+ and -C=O- groups on either side
- These two groups form a weak hydrogen bond
- This causes the chain to twisted into an α-Helix or a β-pleated sheet
What is the tertiary structure of a protein?
- The α-Helix can be twisted and folded even further to give the complex 3D structure of a protein
- Maintained by disulfide bonds (fairly strong), ionic bonds (formed between carboxyl and amino groups but easily broken) and hydrogen bonds (numerous but easily broken)
- The tertiary structure is what can be denatured by heat
- Heat increases the kinetic energy of the molecule and makes parts vibrate faster
- Bonds that hold the protein in the globular shape are broken and complex shape will unravel
- Tertiary shape is what defines the active site on an enzyme
What is the quaternary structure of a protein?
- Protein structure that consists of more than one polypeptide chain that are linked in various ways
- There may be a non protein (prosthetic group)
What are the functions of proteins and an example of each?
- Enzymes e.g. amylase
- Transport e.g. haemoglobin
- Movement e.g. actin and myosin
- Cell recognition e.g. antigens
- Channels e.g. membrane proteins
- Structure e.g. collagen and keratin
- Hormones e.g. insulin
- Protection e.g. antibodies
What are globular proteins?
- Almost spherical in shape
- Soluble in water
- 3D shapes
- α-Helix
E.g. enzymes
What are fibrous proteins?
- Repetitive sequence of amino acids
- Insoluble in water
- Structural
- β-pleated sheet (straight)
E.g. collagen
What is the structure of haemoglobin?
- It is made of 2 α-globin and 2 β-globin polypeptide chains (each with its own tertiary structure)
- Haem area is called a prosthetic group
- A molecule of oxygen can bind to each haem group as it contains
- Conjugated protein as it has a non-protein group attached
What is the structure of insulin?
- Made of two polypeptide chains
- A chain begins with a section of α-helix
- B chain ends with a section of β-pleat
- Both chain are joined by disulfide links
- Hydrophilic R groups are on the outside which makes it soluble in water
What is the structure of amylase?
- Catalyses the breakdown of starch to maltose
- A single chain of amino acids with both α-helix and β-pleated sheet sections
What is the structure of collagen?
- Repeating sequence of amino acids
- Each 3rd amino acid is glycine so it can wind up tightly
- Helix shape
- Made of 3 polypeptide chains wound together like rope
- Hydrogen bonds hold the chain together
- Structural protein
- Found in artery walls, tendons and bones
What is the structure of keratin?
- Rich in cysteine so lots of disulfide bridges between its polypeptide chains
- Alongside hydrogen bonds so the molecule is very strong
- Provides mechanical structure and is waterproof
- Found in fingernails, hair, fur, horns, scales and feathers
What is the structure of elastin?
- Cross-linking and coiling makes the structure strong and flexible
- When subjected to a stretching force, the elastin proteins elongate but remain attached to each other
- Found in lungs, bladder, skin and lining blood vessels
What is the role of calcium?
- Muscle contraction
- Bone formation
What is the role of sodium ions?
- Nerve impulse
- Affects absorption of carbohydrates in the intestine
What is the role of potassium ions?
- Nerve impulse
- Stomatal opening
What is the role of hydrogen ions?
- Production of ATP
- pH determination
What is the role of ammonium ions?
- Production of nitrate ions by bacteria
What is the role of nitrate ions?
- Component of nucleic acid
- Component of the nitrogen cycle
What is the role of hydrogencarbonate ions?
- Involved in the transport of carbon dioxide
What is the role of chloride ions?
- Involved in the transport of carbon dioxide
- Regulates affinity of haemoglobin to oxygen
What is the role of phosphate ions?
- Component of phospholipids, ATP and nucleic acids
- Helps root growth
What is the role of hydroxide ions?
- Involved in regulation of blood pH
