2.2 Biological Molecules Flashcards
what is a covalent bond?
when electrons are shared by atoms
what is a condensation reaction?
when two molecules are joined together with the removal of water
what is a hydrolysis reaction?
when two molecules are split apart with the addition of water
what elements make up carbohydrates?
c, h, o
what elements make up proteins?
c, h, o, n, s
what elements make up nucleic acids?
c, h, o, n, p
what are carbohydrate monomers called?
monosaccharides
what are carbohydrates polymers called?
polysaccharides
what are protein monomers called?
amino acids
what are protein polymers called?
polypeptides / proteins
what are nucleic acid monomers called?
nucleotides
what are nucleic acid polymers called?
DNA / RNA
what is a hydrogen bond?
weak interaction occurring between a slightly negatively charged molecule bonds with a slightly positively charged molecule bonds
why are water molecules described as polar?
2h (slightly positively charged) + o (slightly negatively charged)
what are the advantageous properties of water?
liquid at room temperature, density, solvent, adhesion, surface tension, high specific heat capacity, high latent heat of vaporisation, reactant
how is water being a liquid a useful property?
provides a habitat for aquatic organisms, effective transport medium, reaction medium
why is water a liquid at room temperature?
as water molecules move, they continuously make and break hydrogen bonds. hydrogen bonds make it more difficult for water molecules to escape and become a gas.
is ice more or less dense than water?
less (it floats on top)
why is ice less dense than water?
because of its polar nature, water molecules align themselves in a structure less dense than liquid water at freezing point
how is ice being less dense than water a useful property?
aquatic organisms have a stable environment to live in through winter, layer of ice insulates rest of water against heat loss,
why is water a good solvent?
water is polar so the positive and negative parts of the water molecules are attracted to and cluster around the positive and negative parts of the solute. this separates them, therefore keeping them apart. at this point they dissolve and a solution is formed.
why is water being a good solvent a useful property?
makes water a good transport medium, makes water a good reaction medium
why are water molecules adhesive to each other?
hydrogen bonding between water molecules pulls them together
why does water have surface tension?
water molecules are more attracted to the molecules below them rather than the air above them so water contracts when force is applied
how are adhesion, cohesion and surface tension useful properties of water?
columns of water can be pulled up plant vascular tissues like the xylem, insects such as pondskaters can walk on water
what is specific heat capacity?
the amount of energy need to change the temperature of 1kg of a substance by 1 degree C.
why does water have a high specific heat capacity?
water molecules are held together tightly by many hydrogen bonds therefore lots of energy is needed to increase kinetic energy and break them
why is the high specific heat capacity of water useful?
water doesn’t heat up or cool down easily, provides a stable environment for aquatic organisms to live in and for enzyme-controlled reaction to happen
what is the latent heat of vaporisation?
the amount of energy needed to evaporate water
why does water have a high latent heat of vaporisation?
water molecules are held together tightly by many hydrogen bonds therefore lots of energy is needed to increase kinetic energy and break them
why is the high latent heat of vaporisation of water useful?
mammals are cooled when sweat evaporates
why is water so important as a reactant?
it plays a key role in digestion and the synthesis of large biological molecules
what does it mean when it’s said that carbohydrates are ‘hydrated carbons’?
for every carbon atom, there are 2 hydrogen atoms and 1 oxygen atom
what is the common ending for monosaccharides and polysaccharides?
-ose
what are isomers?
molecules with the same formula, but whose atoms are arranged differently
what are the 2 monosaccharide isomers?
a- glucose and b-glucose
what are the properties of monosaccharides?
sweet, soluble in water
what are the properties of disaccharides?
sweet, soluble in water
what are the most common disaccharides?
maltose, lactose, sucrose
what kind of sugar is maltose?
reducing sugar
what kind of sugar is lactose?
reducing sugar
kind of sugar is sucrose?
non-reducing sugar
a-glucose + a-glucose = ?
maltose
a-glucose + fructose = ?
sucrose
b-galactose + a-glucose = ?
lactose
how can cellobiose be obtained?
via the hydrolysis of the polysaccharide cellulose
what’s the difference between a-glucose and b-glucose?
alpha glucose has the OH group below the H, whilst beta glucose has the OH above the H (ABBA)
what type of bonds hold carbohydrates together?
glycosidic bonds
in which reaction is glucose a reactant?
aerobic respiration
how do plants store energy?
as starch
where do plants keep their energy stores?
chloroplasts, membrane bound starch grains
how do animals store energy?
as glycogen
where do animals keep their energy stores?
muscle cells and liver cells
what are the forms of starch?
amylose and amylopectin
why are starch and glycogen good energy stores?
compact
what is the advantage of energy stores having branched chains?
allow many glucose molecules to be broken down by hydrolysis at the same time when lots of energy is required for respiration
why are polysaccharides less soluble in water than monosaccharides?
bigger size, regions which might bond with water are hidden away inside the molecule
what are the properties of amylose?
a-glucose, straight chains coiled into a spiral, insoluble
what are the properties of amylopectin?
a-glucose, branched chains coiled into a spiral, soluble
what are the properties of glycogen?
a-glucose, smaller chains than starch, doesn’t tend to coil, very branched, insoluble
where is cellulose found in plants?
plant cell walls
what is the structure of cellulose?
b-glucose, straight chains that do not coil but lie side by side,
what is the structure of the cellulose cell wall?
microfibrils run in all directions and criss-cross for extra strength
why is cellulose difficult to digest?
because glycosidic bonds between glucose molecules are hard to break
why is the structure of the cellulose cell wall advantageous?
plants have no rigid skeleton so individual cells need support, space between microfibrils allow water and mineral ions to pass through making the wall permeable, high tensile strength to stop turgid cells bursting
what are bacterial cell walls made of?
peptidoglycan
what are exoskeletons made of?
chitin
why are lipids insoluble in water?
they are not polar
in what substance are lipids soluble in?
alcohol
what are the three types of lipid macromolecules?
triglycerides, phospholipids, steroids
what is the structure of a triglyceride?
one glycerol + 3 fatty acids
what does it mean for a fatty acid to be saturated?
no C=C bond present
what does it mean for a fatty acid to be unsaturated?
a C=C bond is present
which type of fatty acid is liquid?
unsaturated
why are unsaturated fatty acids liquid at room temperature?
the C=C changes the shape of the hydrocarbon chain and gives a kink where the double bond is. this kink pushes the molecules apart and therefore makes them more fluid
what is an example of an unsaturated fat?
oil
what is an example of a saturated fat?
butter
what type of bond is present in a triglyceride?
an ester bond
what are the functions of triglycerides?
energy source, energy store, insulation, buoyancy, protection
how are triglycerides good energy sources?
they can be broken down in respiration to release energy and generate ATP
how are triglycerides good energy stores?
they are insoluble in water and therefore do not affect the water potential of the cell, 1g of fat releases twice as much energy as 1g of glucose
where do mammals store fat?
adipose cells under the skin
why do fats contain more energy than carbohydrates?
have a higher proportion of hydrogen atoms and almost no oxygen atoms
how are triglycerides good insulators?
blubber in whales, nerve cells, animals preparing for hibernation store extra fat
how do triglycerides provide buoyancy?
fat is less dense than water
how do triglycerides provide protection?
humans have fat around delicate organs like the kidneys to act as a shock absorber
what is the structure of a phospholipid?
1 hydrophilic phosphate head + 2 hydrophobic fatty acid tails (commonly one tail is saturated and one unsaturated)
why are phospholipids described as amphipathic?
hydrophilic head and hydrophobic tails
what are the properties of phospholipids in water?
may form a layer on the surface of the water with hydrophobic tails sticking out of the water, or micelles
is the phospholipid bilayer permeable?
only selectively. only small and non-polar molecules can move through the tails in the bilayer
what kind of molecule is cholesterol?
a steroid alcohol
is cholesterol hydrophobic or hydrophilic?
hydrophobic
what is the purpose of cholesterol in the phospholipid bilayer?
regulates fluidity of the membrane and acts as a buffer against ph and temperature changes
where in animals is cholesterol mainly made?
the liver
what is the cholesterol derivative in plants called?
stigmasterol
what is the difference between stigmasterol and cholesterol?
it has a double bond
which steroid hormones are made from cholesterol?
testosterone, oestrogen and vitamin d
can steroid hormones pass through the phospholipid bilayer?
yes, as they are small, hydrophobic, and made from cholesterol
can animals make all the amino acids they require?
they can make some, but must ingest others (called essential amino acids)
can plants make all the amino acids they require?
yes, as long as they have access to fixed nitrogen (such as nitrate)
which amino acid has only 1 H as the R group?
glycine
what is the common ending for amino acids?
-ine, with the exception of acidic R groups such as aspartic acid
what bond joins together amino acids?
peptide bonds
how are proteins digested?
protease enzymes in the intestines break peptide bonds during digestion
what is the primary structure of a protein?
the sequence of amino acids, held together by peptide bonds
what is the secondary structure of a protein?
a-helix or b-pleated sheet, held together by hydrogen bonds
what is the tertiary structure of a protein?
when the a-helix or b-pleated sheet itself starts to fold into either a supercoiled fibrous protein or a spherical globular protein, held together by ionic bonds or disulphide links
what is the quaternary structure of a protein?
how multiple polypeptide chains are arranged to make the complete protein molecule
what type of bond are peptide bonds?
covalent
what are the properties of fibrous proteins?
insoluble in water, regular and repetitive amino acids, strong
what are three examples of fibrous proteins?
collagen, elastin, keratin
what are the properties of globular proteins?
spherical (hydrophobic R groups on inside and hydrophilic R groups on outside), water soluble, often have specific shapes
what are three examples of globular proteins?
haemoglobin, insulin, pepsin
what is the function of collagen?
provide mechanical strength in tendons that connect muscle to bone, artery walls to prevent arteries from bursting due to high blood pressure, bones, cartilage
what is the function of keratin?
provides mechanical protection, impermeable barrier to infection, waterproof so prevents entry of water-borne pollutants and makes body parts hard such as fingernails, hooves, claws, horns, scales, fur, feathers, hair
why is keratin so strong?
rich in cysteine so lots of disulphide links alongside hydrogen bonding
what is the function of elastin?
found where living things must stretch like skin to stretch around bones and muscle, allows lungs to inflate and deflate, allows bladder to expand to hold urine, allows blood vessels to stretch and maintain blood pressure
why is elastin strong and stretchy?
lots of cross-linking and coiling
what is the function of haemoglobin?
carries oxygen from lungs to tissues, oxygen binds to iron, turning haemoglobin from purple to red
what is the structure of haemoglobin?
quaternary structure of 4 polypeptides (2 a-globin chains and 2 b-globin chains) and 1 Fe haem group (prosthetic group makes haemoglobin a conjugated protein)
what is the function of insulin?
binds to glycoprotein receptors on fat and muscle cells to increase their uptake of glucose from the blood therefore reducing the blood glucose concentration
what is the structure of insulin?
2 polypeptide chains, one a-helix and one b-pleat joined together by disulphide links, water soluble
what is the function of pepsin?
digests protein in the stomach
what is the structure of pepsin and how is it related to its function?
single polypeptide chain made of mostly complex amino acids which allows it to remain stable in acidic stomach environment
what are the cations?
Ca2+, Na+, K+, H+, NH4+
what are the anions?
NO3-, HCO3-
what is Ca2+ used for?
increases bone rigidity, important in blood clotting, important in muscle contraction, regulates transmission of nerve impulses, regulates permeability of cell membranes
what is Na+ used for?
involved in the regulation of osmotic pressure and pH maintenance, contributes to nervous transmission and muscle contraction, component of plant vacuoles to maintain turgidity
what is K+ used for?
assists active transport across the cell membrane, involved in the synthesis of glycogen and protein, generates healthy leaves and flowers, contributes to nervous transmission and muscle contraction, component of plant vacuoles to maintain turgidity
what is H+ used for?
involved in photosynthesis, respiration, regulation of blood pH, oxygen and carbon dioxide transport within blood
what is NH4+?
ammonium
what is NH4+ used for?
component of amino acids, vitamins, chlorophyll, nucleic acids, nitrogen cycle, maintains pH of the human body
what is NO3-?
nitrate
what is NO3- used for?
component of amino acids, vitamins, chlorophyll, nucleic acids, nitrogen cycles
what is HCO3-?
hydrogencarbonate
what is HCO3- used for?
involved in regulation of blood pH, involved in transport of carbon dioxide in and out of the blood
what is the condition of lacking a particular ion called?
a deficiency
how do you test for starch?
iodine in potassium iodide solution, turns from brown to blue black if starch is present
how do you test for non-reducing sugars?
Benedict’s test, add Benedict’s solution then heat, blue to orange red if sugar is present (backwards rainbow intensity)
what can this test be used for medically?
to detect glucose in the urine of diabetics
how do you test for reducing sugars?
test a sample for reducing sugars to ensure there are none, boil another sample with hydrochloric acid to hydrolyse the sucrose intro glucose and fructose, use sodium hydrogencarbonate solution to neutralise, test for reducing sugars again, backwards rainbow if present
how do you test for lipids?
emulsion test, mix sample with ethanol, cloudy white emulsion if lipids present
how do you test for proteins?
biuret test, biuret reagent turns from blue to purple if polypeptides are present
what is the qualitative test for non-reducing sugars?
colorimetry
how is chromatography used?
to test for illegal drugs in the urine of athletes, analysis of food to ensure no contamination, analysis of drug purity
