Biological Molecules Flashcards
Carbohydrates, Proteins, Lipids, Fluid Mosaic Model
what elements are carbohydrates made of?
- carbon
- oxygen
- hydrogen
- general formula: Cx(H2O)y
what are the three general types of carbohydrates?
- monosaccharide (basic unit)
- disaccharide (basic unit x2)
- polysaccharide (many basic units)
what are 3 types of monosaccharides?
(CH2O)n
- glucose
- fructose
- galactose
how is a disaccharide formed?
a condensation reaction between two monosaccharides where a water molecule is removed from the pair of monosaccharides to form a glycosidic bond
what are 3 types of disaccharides?
- sucrose (glucose + fructose)
- maltose (glucose + glucose)
- lactose (glucose + galactose)
what is the bond between two monosaccharides?
glycosidic bond
process of disaccharides being separated into monosaccharides?
hydrolysis
- water molecule added to the glycosidic bond
what are polysaccharides?
polymers of monosaccharides
what are 3 types of polysaccharides and their functions?
- starch; storage in plants
- cellulose; structure for plants
- glycogen; storage in humans
characteristics of starch?
- polymer of glucose
- components are amylose and amylopectin
characteristics of amylose?
- glucose within are held by glycosidic bonds
- straight chain structure
- helical shape
characteristics of amylopectin?
- glucose and branches are held by glycosidic bonds
- compact structure
- highly branched structure
what are 2 general functions of carbohydrates?
- source of energy
- monosaccharides are required for the synthesis of nucleic acids, disaccharides and polysaccharides
functions of sucrose and why?
good transport sugar in plants
- soluble; can be moved in high concentrations
- chemically unreactive
functions of glycogen and starch and why?
good storage molecules in humans/plants
- large and insoluble; cannot diffuse through partially permeable membranes
- compact; store more carbohydrates
- lots of branching; easily hydrolysed into monosaccharides
functions of cellulose and why?
good structural polysaccharide in plants
- permeable to water and solutes
- good tensile strength
how to carry out the test for reducing sugars (Benedict’s test)?
- add 2cm3 of test sample into a test tube
- add equal volume of Benedict’s solution
- mix well
- place test tube in boiling water bath for 2 minutes
- observe for color change
observations for Benedict’s test?
- semi-quantitative test
- greater concentration of reducing sugars leads to more brick-red precipitate formed
- if solution remains blue, either no reducing sugars or non-reducing sugars are present
how to carry out a test for non-reducing sugars?
- add 2cm3 of test sample into a test tube
- add a few drops of hydrochloric acid
- heat test tube for 2 minutes in hot water bath
- neutralise the acid by adding sodium hydrogen carbonate until effervescence stops
- perform Benedict’s test
- observe for color changes
what is a common non-reducing sugar?
sucrose
how to test for starch?
- add a few drops of iodine-potassium iodide solution to test sample on a white tile
- observe for color changes
observations for starch test?
starch present: brown solution turns dark blue
starch absent: brown solution remains brown
what elements are proteins made of?
- carbon
- oxygen
- hydrogen
- nitrogen
- sulfur (sometimes)
what are the 5 components of an amino acid?
- carboxyl group (NH2)
- amino group (COOH)
- R group (unique for different amino acids)
- alpha carbon (𝒶 carbon)
- hydrogen atom (bonded to 𝒶 carbon)
how is a peptide bond formed?
condensation reaction between the amino group of an amino acid and the carboxyl group of another, eliminating a water molecule to form a dipeptide
what are the 4 levels of protein structure?
- primary structure
- secondary structure
- tertiary structure
- quaternary structure
definition of the primary structure?
the variety, number and sequence of amino acids in a polypeptide chain
what bond is involved in the primary structure?
peptide bond between amino acids in the polypeptide chain
why is the primary structure of proteins crucial?
variety, number and sequence of constituent amino acids are unique to each protein
definition of the secondary structure?
the localized, repetitive folding of the polypeptide chain
how is the secondary structure stabilized?
intramolecular forces of attraction between peptide linkages of the polypeptide backbone (R groups aren’t involved!)
what are the 3 types of secondary structure?
- 𝒶-helix
- parallel β-pleated sheet
- antiparallel β-pleated sheet
properties of the 𝒶-helix?
- extended spiral spring
- hydrogen bonds between the C=O and -NH groups (from peptide bonds)
properties of the β-pleated sheets?
- two or more regions of the polypeptide chain that lie parallel to one another
- flat zig-zag sheets
- intramolecular forces of attraction between C=O and -NH groups of one part of the backbone to groups of an adjacent part
- polypeptide chains run in the same direction (parallel) or run in opposite directions (antiparallel)
definition of the tertiary structure?
polypeptide chain folds and bends into a precise, compact, globular, three dimensional shape unique to the protein
how is the tertiary structure stabilized?
intramolecular forces of attraction between R groups of amino acids
definition of the quaternary structure?
the combination of a number of polypeptide chains and may involve associated non-protein groups into a large, complex and functional protein molecule
how is the quaternary structure stabilized?
subunits (polypeptide chains) are held by intermolecular forces of attraction
what are the 8 functions of proteins?
- homeostatic; act as buffers that stabilize pH in blood plasma
- enzymatic; act as enzymes that speed up chemical reactions
- hormonal; act as hormones in the body
- transport; present in plasma membranes to transport substances in and out of cells (eg. haemoglobin and lipoproteins for cholesterol transport in blood)
- storage (eg. ferritin stores iron in liver and myoglobin stores oxygen in skeletal muscle cells)
- protection (eg. antibodies, fibrinogen and thrombin)
- structural (eg. collagen for connective tissues and keratin for hair)
- source of energy; when carbohydrates and fats are depleted)
how to test for proteins (biuret test)?
- add 2cm3 of test sample into a test tube
- add an equal solution of 5% sodium hydroxide solution
- add 2 drops of 1% copper sulfate solution
- mix well
- observe for color changes
observations from the biuret test?
proteins present: light blue solution turns violet
proteins absent: light blue solution remains light blue
what elements are lipids made of?
- carbon
- hydrogen
- oxygen (less than hydrogen)
difference between fats and oils?
- if solid at 20°C, is a fat
- if liquid at 20°C, is an oil
what are simple lipids?
fats: esters of fatty acids with glycerol
waxes: esters of fatty acids with complex alcohol
what is glycerol?
an alcohol made of 3 carbons, each bearing a hydroxyl group (-OH)
what are compound lipids?
simple lipids + non-lipid components
what are fatty acids?
- consists of a hydrocarbon chain and carboxyl group (-COOH)
- hydrocarbon chain consists of carbon atoms with hydrogen atoms attached to it
characteristics of saturated fatty acids?
- has no C=C double bond
- no kinks
- higher m.p.
- more solid (fats)
- creates saturated fats
- from animals
characteristics of unsaturated fatty acids?
- has C=C double bond (if more than one carbon-carbon double bond, it is polyunsaturated)
- has kinks
- lower m.p.
- more liquid (oils)
- creates unsaturated fats
- from plants
what is a molecule of triglyceride made of?
three fatty acid molecules combined with a molecule of glyceride, held by an ester bond
how is an ester bond formed?
condensation reaction where one molecule of water is removed from the hydroxyl group in the glycerol and carboxyl group from the fatty acid
what are the 5 functions of lipids?
- a form of storage of energy (eg. triglycerides)
- good thermal insulator
- protects delicate organs
- component of the cell membrane (eg. phospholipid)
- improves buoyancy of an organism (blubber)
how to test for lipids?
- add 2cm3 of ethanol to two drops of the test sample
- decant the ethanol into another test tube containing 2cm3 of water
- mix well
- observe for cloudiness
observations from the lipid test?
lipid present: homogeneous solution formed with ethanol, and white emulsion formed when water is added
lipid absent: homogeneous solution formed with ethanol, solution remains homogeneous when water is added
what does a phospholipid molecule consist of?
- 2 fatty acid chains (one unsaturated and one saturated) linked to 2 of 3 carbons of the glycerol molecule
- phosphate group is attached to the last carbon
what is the fluid mosaic model?
fluid refers to the phospholipid and and embedded proteins moving freely and laterally within the phospholipid bilayer
mosaic refers to the protein and cholesterol molecules that are randomly embedded and scattered among the phospholipid molecules, resulting in a mosaic arrangement
what are the components of the cell membrane?
- channel and carrier proteins; to allow the passage of specific ions and molecules across the membrane
- enzymes; to catalyze reactions
- receptors; specific binding sites to allow chemical messengers to bind to the protein to relay messages to the inside of the cell
- glycoproteins and glycolipids; for cell to cell recognition and cell adhesion
what are glycolipids?
carbohydrates molecules covalently bonded to phospholipid molecules
how is membrane fluidity affected?
- the more the unsaturated fatty acids, the greater the fluidity
- the more the saturated fatty acids, the lower the fluidity
- cholesterol increases fluidity at low temperature and decreases fluidity at high temperatures
what is simple diffusion?
- passive process
- no transport proteins involved
- small molecules and hydrophobic molecules
- no energy required from hydrolysis of ATP
molecules that can pass through the cell surface membrane through simple diffusion?
- oxygen
- carbon dioxide
- nitrogen
- water (polar; hydrophilic)
- glycerol (polar; hydrophilic)
what is facilitated diffusion?
- transport proteins involved to transport hydrophilic molecules
- passive process
- transport proteins are specific
what do channel proteins do?
they provide a hydrophilic passage to move hydrophilic molecules across the hydrophobic core of the cell membrane
what do carrier proteins do?
they change shapes to move the hydrophilic molecule across the cell membrane triggered by the binding and release of the molecule at the binding site
they shield the hydrophilic molecules from the hydrophobic core of the cell membrane
what is active transport?
- movement of molecules from a lower concentration region to a higher concentration region
- requires energy from the hydrolysis of ATP
- carrier proteins involved
