Biological Molecules - Carbohydrates, Lipids and Proteins Flashcards
Define a monosaccharide
The monomer of a carbohydrate
Name 3 monosaccharides
Glucose
Fructose
Galactose
What is the structural difference between alpha and beta glucose?
The hydroxyl and hydrogen groups on the right of the molecules are flipped
Define a disaccharide
A disaccharide consists of 2 monosaccharides bonded with a glycosidic bond
Name 3 examples of disaccharides
Maltose
Sucrose
Lactose
What are the monosaccharides of maltose?
2 alpha glucose
What are the monosaccharides of sucrose?
Glucose and fructose
What are the monosaccharides of lactose?
Glucose and galactose
What is a structural polysaccharide found in animals?
Chitin
What are 3 examples of polysaccharides?
Cellulose
Glycogen
Starch
What are the monosaccharides of cellulose?
Chains of beta glucose
What are the monosaccharides of glycogen
Chains of alpha glucose
What are the monosaccharides of starch?
Chains of alpha glucose
What are 3 examples of hexoses?
Glucose
Fructose
Galactose
Define a condensation reaction
The process where 2 monomers form a covalent bond and a H20 molecule is lost
Define hydrolysis
The process where water is added to a polymer under certain conditions, breaking the covalent bond and releasing the individual monomers
Describe the Benedict’s test for sugars
- add an excess of Benedict’s reagent (blue)
- Heat in a boiled water bath
- If the test is positive, a coloured precipitate will form
- Green (very low), Yellow (low), Orange (medium), Red (high)
What is the structure of glycogen and where is it found?
Glycogen consists of multi-branched, short chains of alpha glucose
It is found in animals (liver and muscles) and plants
Insoluble and large
What is the function of glycogen?
Storage molecule
Synthesized from alpha glucose when blood sugar levels are too high
Can be easily broken down into an energy source when blood sugar levels are too low
How does the structure of glycogen help its function?
Glycosidic bonds are easily broken by water
Multiple branches provide quick breakdown
Low osmotic potential means it doesn’t diffuse in and out of cells and also doesn’t affect the volume of water of cells
What is structure of starch?
Starch consists of alpha glucose chains and specific to plants only
The 2 types are amylose (unbranched) and amylopectin (branched)
Forms close spirals and is insoluble
What is the function of starch?
It is designed for use in respiration and long term storage in plants
Used when there is limited light -> less photosynthesis
Stored in seeds in order for them to grow before they can photosynthesise
How does the structure of starch help its function?
The long chains wind up tightly
- efficient storage
- Monomers can be hydrolyzed for energy use
- Amylopectin used for shorter term energy release as it is branched
- Amylose used for longer term energy release as it is unbranched
What is the structure of cellulose?
Chains of beta glucose, resulting in every other molecule being flipped
Flipped molecules can form hydrogen bonds with the parallel chain below, forming a strong, rigid polymer
What is the function of cellulose?
To provide structure - it makes up 30% of the cell wall in plants
How does the structure of cellulose help its function?
The beta glucose linkages gives it a flat a rigid structure which helps it to provide structure throughout different organisms
What are the properties of lipids?
Double energy:mass ratio than carbohydrates
Insoluble in water but soluble in organic substances
High ratio of H:O so releases water when oxidised
What are the functions of lipids?
Energy storage molecules
Waterproofing
Insulation
Physical protection
What are the major differences between fats and oils?
Fats: Solid at 10 - 20 degrees, saturated
Oils: Liquid at room temp , unsaturated
What are the 3 types of triglyceride tails?
- Saturated -> no double bonds
- Unsaturated -> one double bond
- Polyunsaturated -> multiple double bonds
What is the structure of a triglyceride?
3 fatty acid tails combined with a glycerol head by an ester bond
Define a phospholipid?
Similar to lipids except one fatty acid is replaced with a phosphate molecule
What is the relationship between phospholipids and water?
Phospholipids have a hydrophilic head and a hydrophobic tail
This causes them to form structures such as lipid bilayers in water
What are amino acids composed of?
Centre alpha C
Solitary H branch
Amino group
Carboxyl group
R (variable) group
How many amino acid variations are there?
20
What feature of amino acids provides indirect evidence for evolution?
The same 20 amino acids occur in all living organisms
How many structural levels occur in proteins?
Proteins can have up to 4 levels of structure
Some only need 3 -> only the large proteins have quaternary structure
What is the primary structure of proteins?
The synthesis of amino acids into a polypeptide chain
What is the secondary structure of proteins?
This occurs as H bonds form between the H+ ions and O- ions of the carboxyl group
These bonds are relatively weak but contain enough strength to fold the polypeptide chain into a 3D shape
What are 2 examples of shapes formed in secondary structure?
Alpha helix
Beta pleated sheet
What is the tertiary structure of proteins?
Result of further twisting of the secondary structure
Can be complex and is specific to the protein
Plays a significant role in determining the behaviours of the protein
Maintained by 3 types of bonds
What are the 3 types of bond that maintain tertiary structure?
Disulfide bonds - strong and not easily broken
Ionic bonds - formed between the carboxyl and amino groups that weren’t involved in peptide bonds, weaker than disulfide bonds and easily broken by pH changes
Hydrogen bonds - numerous but easily broken
What is the quaternary structure of proteins?
Multiple polypeptides bond together eg Haemoglobin
If 2 proteins have the same and type of amino acids, why will they have different tertiary structures?
The amino acids are in different orders
This means that different hydrogen, ionic and disulfide bonds will form, twisting the polypeptide into a different shape
What is the test for lipids?
The Emulsion Test
Add ethanol to the sample in a 5:2 ratio of ethanol:sample
If lipids are present, a white emulsion will form
What are the types of proteins?
Fibrous proteins eg collagen
Globular proteins eg enzymes
What is the function of a fibrous protein?
Fibrous proteins have structural functions eg collagen is found in tendons (joining muscles to bones)
What is the function of a globular protein?
Globular proteins perform metabolic functions eg enzymes catalyse digestion
How are the structures of fibrous and globular proteins different?
Fibrous proteins have a quaternary structure with 2 other polypeptide chains
Globular proteins only have a tertiary structure, not quaternary
Describe the structure of collagen and how it is formed
Primary Structure -> coiled chain
Secondary Structure -> tightly coiled into an alpha helix
Tertiary Structure -> also an alpha helix
Quaternary Structure -> 3 double coiled polypeptide chains wound together
What is the tertiary structure of haemoglobin?
2 alpha helices and 2 beta pleated sheets
