1A Biological Molecules Flashcards
What is a monomer? Give example
A single subunit of life, a molecule that can be bonded to other identical molecules to form a polymer eg. fructose
What is a polymer? Give examples
A long and complex chain of monomers bonded together with covalent bonds eg. DNA or enzymes
Describe the structure of amylose
A long chain of alpha glucose molecules, coiled in a spiral, two free ends per chain, only has 1,4 glycosidic bonds
Describe the structure of amylopectin
A branched chain of alpha glucose molecules, has more than 2 free ends, has both 1,4 and 1,6 glycosidic bonds
Describe the structure of glycogen
Same as amylopectin (branched chain of a-glucose molecules consisting of 1,4 and 1,6 glycosidic bonds) but has more branches so has more free ends
What is a monosaccharide?
A monomer of sugar that can’t be hydrolysed to form a simpler sugar
What is a condensation reaction?
The reaction that forms large biological molecules. It releases water and bonds the smaller components together into larger molecules
What is produced in the condensation of amino acids?
Proteins
What is produced in the condensation of 2 monosaccharides?
A disaccharide
What is produced in the condensation of fatty acids and monoglycerides?
Lipids
What may the glucose produced by plants in photosynthesis be converted into?
Insoluble starch for storage
What do the chemical reactions that occur during aerobic respiration use and what for?
Glucose and oxygen to release energy
What is some glucose in plants and algae used to produce?
Fat for storage, cellulose which strengthens the cell wall and proteins
What are protein molecules made up of and why are they folded?
Made up of long chains of amino acids. These chains are folded to produce a specific shape that enables other molecules to fit into the protein
What tissues do proteins act as structural components of?
Tissues such as muscles, hormones, antibodies and catalysts
What do catalysts do and what are biological catalysts known as?
Catalysts increase the rate of chemical reactions, biological catalysts are proteins called enzymes
Why is the shape of an enzyme important and what does high temperature do to the shape?
The shape of an enzyme is vital for its function and high temperature changes their shape
Why is pH significant to enzymes?
Different enzymes work best at different pH values
What is covalent bonding?
When atoms share a pair of electrons in their outer shells. As a result the outer shell of both atoms is filled and a more stable compound known as a molecule is formed
What is ionic bonding?
When ions with opposite charges attract one another. This electrostatic connection is known as an ionic bond. eg. Na+ and Cl- form NaCl. Ionic bonds are weaker than covalent ones
What is hydrogen bonding?
When the electrons within a molecule aren’t evenly distributed but tend to spend more time at one position. This region is more negatively charged than the rest of the molecule. A molecule like this is polarised/ is a polar molecule.
How do molecules form hydrogen bonds?
The more negatively charged region of one molecule attracts the more positively charged region of another and a weak electrostatic attraction is formed between the molecules.
How can important forces be formed by hydrogen bonds and what can these do?
Each hydrogen bond is individually weak but they can collectively form important forces that alter the physical properties of molecules. eg. water
What is polymerisation?
The process when monomers are linked to form long chains called polymers
How are polynucleotides made?
Condensation reactions of nucleotides forms polynucleotides (nucleic acids)
How are polysaccharides made?
Condensation reactions of monosaccharides forms polysaccharides (carbohydrates)
How are lipids made?
Condensation reactions of a glycerol molecule and 3 fatty acid molecules forms a lipid and 3 H2O molecules
How are polypeptides made?
Condensation reactions of amino acids forms polypeptides (proteins)
What is metabolism?
All the chemical processes that take place in living organisms
What is a molar solution?
A solution that contains one mole of solute in each litre of solution (each litre contains the molecular weight of the solute in grams, eg. a mole of NaCl = 58.5g so a molar solution of salt is a litre of solution with 58.5g of sodium chloride)
What is a mole?
The unit for measuring the amount of substance. One mole contains the same amount of particles as 12g of the carbon-12 isotope. 12g of carbon-12 contains 6.022x10²³ atoms.
What is the Avogadro constant?
6.022x10²³
What is an atom?
The smallest units of a chemical element that can exist independently. An atom comprises a nucleus with protons and neutrons and tiny particles called electrons that orbit the nucleus of the atom
What are the main features of neutrons?
Occur in the nucleus of an atom and have the same mass as protons but no electrical charge
What are the main features of protons?
Occur in the nucleus of an atom and have the same mass as neutrons but do have a positive charge
What are the main features of electrons?
Orbit in shells around the nucleus but a long way from it, they have such a small mass that their contribution to the overall mass of the atom is minuscule. They’re negatively charged and the amount of them determines the chemical properties of the atom
What is the atomic number of an atom?
The number of protons in an atom
What is the mass number of an atom?
The total number of protons and neutrons in an atom
What is an isotope?
When the amount of neutrons in an atom varies however the proton number remains the same
How does an atom become an ion?
If it loses or gains an electron, loss makes a positive ion and gain makes a negative ion (more than one electron can be lost or gained eg. Ca2+)
What is carbon’s unusual feature and what does it allow?
Carbon atoms very readily form bonds with other carbon atoms which allows long chains of carbon atoms to be built up to various lengths. These backbones can have other atoms attach to them which allows creation of many different carbon molecules, all based on carbon
What is the variety of life on earth a consequence of?
Living organisms being based on the versatile carbon atom
What are organic molecules?
Carbon containing molecules
Why is life based on a small number of chemical elements?
In living organisms there are relatively few atoms that attach to carbon
What are most polymers made up of?
Just four elements: carbon, hydrogen, oxygen and nitrogen
What are the names of monomers and polymers of carbohydrates?
Basic monomer unit is a sugar (saccharide), single monomer is a monosaccharide, a pair of monosaccharides can be combined to form a disaccharide or more than two can be combined to form a polysaccharide
What are the properties of monosaccharides?
Sweet-tasting, soluble substances that have a general formula (CH2O)n where n is any number from 3-7
What are the isomers of glucose?
Alpha glucose and beta glucose
What is reduction?
A chemical reaction involving the gain of electrons or hydrogen
What is a reducing sugar? Give examples
A sugar that can donate electrons to (or reduce) another chemical eg. Benedict’s reagent. Examples of reducing sugars are all monosaccharides and some disaccharides eg. maltose
What is the test for a reducing sugar?
The Benedict’s test
Describe the Benedict’s test
- add 2cm³ of the food sample to be tested to a test tube, if it is not already a liquid then grind it up in water
- add an equal volume of Benedict’s reagent
- heat the test tube in a gently boiling water bath for 5 minutes
Explain the Benedict’s test
Benedict’s reagant is an alkaline solution of copper(II) sulphate. When a reducing sugar is heated with Benedict’s reagent it forms an insoluble, red precipitate of copper(I) oxide. This causes the colour change in a positive test.
What kind of test is the Benedict’s test?
A semi-quantitative test, it can be used to estimate the approximate amount of reducing sugar in the sample
What colour does the Benedict’s test show depending on the amount of reducing sugar in the sample?
Blue=none, green=very low, yellow=low, orange=medium, high=red
What is maltose?
A disaccharide formed by two alpha glucose monosaccharides
What is sucrose?
A disaccharide formed by two monosaccharides- alpha glucose and fructose
What is lactose?
A disaccharide formed by two monosaccharides- alpha glucose and galactose
What happens when two monosaccharides join?
A molecule of water is removed, a condensation reaction occurs and this forms a glycosidic bond between the monosaccharides. This therefore produces a disaccharide and a molecule of water
What happens when water is added to a disaccharide? (assume suitable conditions are present)
It breaks the glycosidic bond and releases the previous monosaccharides (one molecule of water is needed to break on disaccharide). This is called hydrolysis.
What would happen if a non-reducing sugar was tested with the normal Benedict’s reagent method?
The colour would not change when the sugar is heated with the reagent
What must be done to a non-reducing sugar before you test it with Benedict’s reagent?
It must be hydrolysed into its monosaccharide components by hydrolysis
How would you hydrolyse a non-reducing sugar sample?
- If not in liquid form then grind up with water
- Add 2cm³ of the food sample being tested to 2cm³ of dilute hydrochloric acid in a test tube
- Place the test tube in a gently boiling water bath for 5 minutes (the acid will hydrolyse any disaccharide into its constituent monosaccharides)
- Slowly add some sodium hydrogencarbonate solution to the test tube in order to neutralise the hydrochloric acid
- Test with pH paper to check the solution is alkaline
- Retest the sample with 2cm³ of Benedict’s
- If there was a non-reducing sugar in the original sample the Benedict’s reagent will now turn orange-brown
Why must a sample be alkaline before it’s tested with Benedict’s reagent?
Benedict’s reagent doesn’t work in acidic conditions
What do condensation reactions form?
Glycosidic bonds
Are polysaccharides insoluble or soluble? Why is this beneficial?
They are insoluble which makes them suitable for storage. When they are hydrolysed they break into monosaccharides or disaccharides.
Give an example of a polysaccharide whose function is not storage
Cellulose- instead it has properties which make it great for giving structural support to plant cells
Give an example of where starch is found in plants
Starch is a polysaccharide found in many parts of plants in the form of small granules or grains eg. starch grains in chloroplasts. It is formed by the joining of between 200 and 100 000 alpha glucose molecules
Why is starch easily detected?
It has the ability to change the colour of the iodine in potassium iodide solution from yellow to blue-black
In what condition is the test for starch conducted?
At room temperature
Describe the method for the test for starch
- Place 2cm³ of the sample being tested in a test tube (or two drops of it into a depression on a spotting tile)
- Add two drops of iodine solution and shake or stir
- If starch is present the solution will turn blue-black, if not there will be no change
Where do particularly large amounts of starch occur in plants?
Seeds and storage organs such as potato tubers
Describe starch
Forms an important component of food and is the major energy source of most diets. Made up of chains of alpha glucose molecules linked by glycosidic bonds. The chains may be branched (amylopectin) or unbranched (amylose). The unbranched chain is wound into a tight spiral coil that makes it a very compact molecule
How is starch’s structure suited for energy storage?
- it is insoluble and doesn’t affect water potential so water is not drawn into the cells by osmosis
- it is large and insoluble so it doesn’t diffuse out of cells
- it is compact so a lot can be stored in a small space
- when hydrolysed it forms alpha glucose which is easily transported and readily used in respiration
- the branched form has many ends which means they can be acted on simultaneously by enzymes so glucose monomers are released rapidly
What is an animal cell’s version of starch?
Glycogen
Where is glycogen found?
Animals and bacteria but never plant cells
How is the structure of glycogen different to the structure of starch?
It is branched like starch but the branches are shorter and more frequent
How and where is glycogen stored in animals?
As small granules mainly in the muscles and liver
Why is the mass of carbohydrate stored in animals relatively small?
Animals’ main storage molecule is fat
How does glycogen’s structure suit it for storage?
- it is insoluble so therefore doesn’t tend to draw water into the cells by osmosis
- as it is insoluble, it doesn’t diffuse out of cells
- it is compact so lots can be stored in a small space
- it is more highly branched than starch so has more ends that can be simultaneously acted on by enzymes, therefore it is more rapidly broken down to form glucose monomers which are used in respiration.
Why is it important that glycogen can be broken down quicker in animals than starch can be broken down in animals?
This is important to animals which have a higher metabolic rate and therefore respiratory rate than plants because they are more active and therefore need a quicker and higher release of energy
How is the structure of cellulose different to the structure of glycogen and starch and what does this difference cause?
It is made from monomers of beta glucose not alpha glucose which causes fundamental differences in the structure and function of this polysaccharide.
Cellulose has straight unbranched chains (not coiled) that run parallel to eachother, this allows hydrogen bonds to form cross-links between adjacent chains.
How do hydrogen bonds between cellulose chains add strength to cellulose?
While each individual bond may be fairly weak, the sheer amount of them overall forms a considerable contribution to strengthening cellulose which makes it the valuable structural material that it is
How are beta glucose molecules arranged in the structure of cellulose?
They are alternate ways up, 1st is right side up and the 2nd is flipped upside down
What is cellulose a major component of and how does it help in this area?
Major component in plant cell walls and provides rigidity to the plant cell and also prevents it from bursting when water enters the cell through osmosis. It does this by exerting an inward pressure that stops any further influx of water
What is the result of cellulose exerting an inward pressure on cells to stop an influx of water?
Living plant cells are turgid and push against one another making non-woody parts of the plant semi-rigid
Where is it important in plants for the cells to be turgid and make non-woody parts of the plant semi-rigid and why?
Important in maintaining stems and leaves in a turgid state so that they can provide the maximum surface area for photosynthesis
How is cellulose suited for its function of providing support and rigidity through its structure?
- cellulose molecules are made up of beta glucose molecules so form long straight, unbranched chains
- these chains run parallel to each other and are crossed linked by hydrogen bonds which add collective strength
- these molecules are grouped to form microfibrils which in turn are grouped to form fibres all of which provides yet more strength
What characteristics do all lipids share?
- they contain carbon, hydrogen and oxygen
- the proportion of oxygen to hydrogen and carbon is smaller than in carbs
- they are insoluble in water
- they are soluble in organic solvents such as alcohols and acetone
What are the main groups of lipids?
Triglycerides (fats and oils) and phospholipids
What are some roles of lipids?
- cell membranes
- source of energy
- waterproofing
- insulation
- protection
How can you distinguish between fats and oils?
Oils are liquid at room temperature, fats are solid
How are lipids involved in sourcing energy?
When oxidised, lipids provide more than twice the energy as the same mass of carbohydrate and they release water
How are lipids involved in waterproofing of plants, insects and mammals?
Lipids are insoluble in water and therefore useful as a waterproofing. Both plants and insects have waxy, lipid cuticles that conserve water. Similarly mammals produce an oily secretion from their sebaceous glands in the skin
How are lipids involved in insulation?
Fats are slow conductors of heat and, when stored beneath the body surface, they help retain body heat. They also act as electrical insulators in the myelin sheath around nerve cells
How are lipids involved in protection?
Fat is often stored around delicate organs for protection eg. kidney
What is a triglyceride?
3 fatty acids combined with glycerol. Each fatty acid forms an ester bond with glycerol in a condensation reaction
What would hydrolysis of a triglyceride produce?
Glycerol and 3 fatty acids
What is the difference between a reducing and non-reducing sugar?
A reducing sugar can donate an electron
Give an example of a reducing and non-reducing sugar?
R= glucose, NR= sucrose
Describe the test for a reducing sugar
Semi-quantitative Benedict’s test:
5cm3 of sample and 5cm3 of Benedict’s reagent in test tube in a 80C water bath for 5 mins. Positive test blue turns to green, yellow, orange or red depending on how much sugar is in the sample
Describe the test for a non-reducing sugar
Hydrolyse the non-reducing sugar to make it reducing then do the semi-quantitative test as normal:
Add 5cm3 HCl acid to 5cm3 of sample and put in a boiling water bath. After 3 mins, neutralise with sodium hydrogen carbonate and add in excess to make the solution alkaline.
Why does a solution need to be alkaline before performing the Benedict’s test?
Benedict’s reagent won’t work on an acidic sample
What are the 3 different structures for lipids?
Saturated, monounsaturated and polyunsaturated
Describe a saturated lipid
A lipid with no double bonds between any carbon atoms
Describe a monounsaturated lipid
Just one double bond between carbon atoms
Describe a polyunsaturated lipid
More than one double bond between carbon atoms
Why are double bonds significant within lipid structures?
Double bonds cause bends in the molecules and bends cause weaker forces between molecules
Describe how to carry out the starch test
- Place food samples in dimples of spotting tile
- Add 2-3 drops of 0.01M iodine
POSITIVE RESULT: yellow/brown changes to blue/black
Describe how to carry out the protein test (Biuret)
- Place food samples in dimples of spotting tile (some may need crushing with a glass rod)
- Add enough Biuret solution to fill the tiles
POSITIVE RESULT: turns purple
Describe how to carry out the protein test (sodium hydroxide and copper sulphate)
- Mix equal volumes of 0.4M sodium hydroxide and the food sample (for solid food samples, first mix the sample with 2-3ml of water)
- Use a pipette to slowly add 0.01M copper (II) sulphate (VI) down the side of the test tube into the mixture
POSITIVE RESULT: purple ring forms on surface of the mixture
Describe the test for lipids (grease spot)
Rub or drip the sample on grease-proof or filter paper
POSITIVE RESULT: a translucent grease spot is formed which doesn’t evaporate after 20 mins (like water)
Describe the test for lipids (ethanol)
- Add an equal volume of the sample and ethanol into a test tube
- Cover the top of the tub with a bung and shake
POSITIVE RESULT: a cloudy emulsion forms
Describe the test for lipids (Sudan III)
- Dab food sample onto a piece of filter paper using a glass rod
- Leave the sample to dry
- Add a drop of Sudan III
POSITIVE RESULT: red/orange droplets will form on the spot
In colorimetry of the quantitative Benedict’s tests, why does relative absorption increase as glucose concentration decreases?
If there is lower glucose concentration, then less Benedict’s reagent reacts so less white precipitate is formed and more blue chemical is left in solution so more light is absorbed in the colorimeter due to the darker coloured solution.
What kind of bonds are there in triglycerides?
Ester linkages formed through condensation reactions
What do lipids form a major part of?
Plasma membranes
What are the two groups of lipids?
Triglycerides and phospholipids
What are functions of proteins?
- in cell membranes for transport (active transport)
- in enzymes (metabolic reactions)
- in haemoglobin (transport of oxygen)
- in keratin (hair and nails)
- in muscles (movement)
- in antibodies and antigens (for immunity and cell recognitions)
- digestive enzymes (for digestion eg. lipase)
What is the general structure of an amino acid?
A central carbon atoms surrounded by:
- a hydrogen atom
- a carboxyl group (COOH)
- an amine group (H2N)
- an R group
What is the R group of an amino acid?
It’s unique to each of the 20 amino acids
What are amino acids and what do they join to become?
Amino acids are monomers and join together to make the polymer of protein
What determines the function of a protein molecule?
The sequence, type and number of the amino acids within a protein determines its shape and therefore function
What is a peptide bond?
A chemical bond formed between 2 molecules when the carboxyl group of one reacts with the amino group of the other (condensation reaction)
What is the primary structure of a protein?
The order and length of the amino acid chain. It determines the ultimate shape of the protein. A simple chain of amino acids known as a polypeptide and joined with peptide bonds.
What is the secondary structure of a protein?
A shaped chain of amino acids due to hydrogen bonds eg. a-helix and b-pleated sheets
What is the tertiary structure of a protein?
When sheets and helices are twisted and folded even more into a 3D structure
What do the bonds within the tertiary structure of a protein include?
- disulphide bridges: fairly strong and not easily broken, formed between 2 cysteine amino acids
- ionic bonds: formed between any carboxyl group and amino groups which aren’t part of a peptide bond, these are weaker than disulphide bridges and are easily broken by changes in pH
- hydrogen bonds: numerous but easily broken
What is the quaternary structure of a protein?
2+ polypeptide chains combined into a large, complex protein molecule eg. haemoglobin
Describe an enzyme
- proteins that speed up biological reactions
- active sites have specific shapes (dependent on the sequence of amino acids within the polypeptide forming the enzyme)
- globular in shape
- used over and over again because their shape is maintained
What do enzymes do to a reaction?
They lower the activation energy of the reaction via forming enzyme-substrate complexes
What does the ‘induced fit’ model show for enzymes?
The enzymes change shape when an appropriate substrate molecule binds to an active site
What limiting factors are there for enzymes?
Temperature, pH, enzyme conc, substrate conc, enzyme inhibitors
What is an optimum temperature for enzymes?
The temperature at which the enzyme works at its maximum rate
What effect may lower temperatures have on enzymes?
Lower temperatures slow the movement of substrates and enzymes and therefore lower the amount of collisions and the rate of success of them
What effect may higher temperatures have on enzymes?
They will speed up enzyme function to a point then the rate of reaction will decrease drastically as the enzymes begins to denature (bonds within the tertiary structure of the enzyme begin to weaken and break so the shape of the enzyme and its active site changes meaning the substrate can no longer fit into it)
How can extreme levels of pH denature an enzyme?
An excess of H+ or OH- ions causes hydrogen bonds and ionic bonds within the tertiary structure of the enzyme to break which changes the shape of the active site
What is complete denaturation of an enzyme?
When substrates will no longer bind with an active site at all
How does substrate concentration affect enzyme function?
Greater substrate concentration means a higher rate of reaction because the chance of successful collisions is greater and therefore enzyme-substrate complexes are more likely to form
When would increasing the substrate concentration not affect the rate of enzyme function?
If enzyme concentration is the limiting factor because all the active sites will be occupied (saturated) so more substrates have no effect. (they are queuing up)
How does enzyme concentration affect the rate of enzyme function?
Higher enzyme concentration means more active sites and greater chance of substrate colliding with one therefore greater chance of enzyme-substrate complexes forming
How does the rate of reaction increase when enzyme concentration is increased (depending on the limiting factor)?
If there is sufficient substrate, the rate of reaction will increase linearly with the enzyme concentration. If the substrate concentration is the limiting factor, increasing the enzyme concentration has no effect
What are the 2 types of enzyme inhibitors?
- Competitive: similar shape to substrate and therefore competes with them for the active site
- Non-competitive: bind to enzyme at an alternate site which alters the active site shape and prevents binding of substrate
What can reversible inhibitors act as in metabolic pathways?
Regulators
Why must metabolic reactions be tightly controlled and balanced?
So that no enzyme ‘runs wild’ and produces too much of one product
Describe how metabolic reactions can be controlled by using the end product off a particular sequence of metabolic reactions.
The end product can be used as a non-competitive, reversible inhibitor
Explain how the end product of a metabolic reaction can be used as a reversible inhibitor.
As the enzyme converts substrate to product, the process slows itself down as the end product bonds to the alternative site of the enzyme and alters the shape of the active site. This prevents enzyme-substrate complexes forming which slows rate of reaction down gradually.
How does the active site of the enzymes reform after the end product of a reaction has been used as a reversible inhibitor?
The end product can detach from the enzyme to be used elsewhere which allows the active site to reform and for the enzyme to return to an active state
How is a continuous feedback loop created when an end product reversible inhibitor is used to control the rate of a reaction?
As product level falls, the rate of reaction increases and vice-versa
What effect does each type of inhibitor have on enzyme activity?
Both types slow down or stop enzyme activity. An increase of inhibitor concentration causes a decrease in rate of reaction and eventually if inhibitor concentration continues to rise, the rate of reaction will reach 0
Can the effect of each type of inhibitor be countered by increasing substrate concentration?
Competitive: increasing substrate concentration DOES counter the inhibitor and increases the rate of reaction
Non-competitive: increasing substrate concentration DOES NOT counter the inhibitor and DOES NOT increase the rate of reaction
Explain how a higher concentration of substrate affects the rate of reaction with a competitive inhibitor
Comp inhibitors compete for the active site so a higher conc of substrate gives them a better chance at getting the active site. Comp inhibitors also don’t affect the maximum potential they just affect the time it takes to get there
Explain how a higher concentration of substrate affects the rate of reaction with a non-competitive inhibitor
Non-comp inhibitors affect the maximum potential as they prevent substrates from binding to the enzyme at all, a higher conc of substrates is ineffective
What is DNA made up of?
Nucleotides
What 3 things make up nucleotides?
A Pentose sugar (deoxyribose), a phosphate group and an organic base
What are the 4 organic bases found in DNA?
Adenine, cytosine, guanine and thymine
What is specific base pairing and when does it occur?
- Base pairing occurs between complementary bases
- Adenine always pairs with thymine
- Guanine always pairs with cytosine
How many hydrogen bonds form between adenine and thymine?
2
How many hydrogen bonds form between cytosine and guanine?
3
What do sugars and phosphates in DNA join to form and what is this thing held together by?
They join to form a sugar-phosphate backbone which is held together by strong phosphodiester bonds
What is a polynucleotide and how is it formed?
A chain of two or more nucleotides (2 nucleotides are a dinucleotide) formed by condensation reactions
Which two things does the condensation reaction occur between in the formation of a polynucleotide?
A hydroxyl group in the phosphate group of one nucleotide and a hydroxyl group attached to the carbon 3’ particle of another nucleotide
What is the overall structure of DNA?
- Double helix structure with a major groove and a minor groove
- DH consists of two strands of DNA (2 polynucleotides) which are joined by hydrogen bonds between base pairs
- Two strands are complementary of eachother ie. when one has G the other has C etc.
What 3 things is RNA made up of?
A phosphate group, a Pentose sugar (ribose) and an organic base
What are the organic bases of RNA?
Adenine, cytosine, guanine and uracil
What is the overall structure of RNA?
- In much shorter chains than DNA
- RNA can come in single chains whereas DNA comes in pairs or RNA may come in a clover shape
What is the difference between a single strand of RNA compared to a clover shaped molecule of RNA?
Single strand is mRNA (messenger RNA)
Clover shaped is tRNA (transfer RNA)
(Both have uracil instead of thymine)
What does DNA’s double helix structure enable?
For DNA to act as a stable information-carrying molecule
How do the double helix and sugar-phosphate backbone structure increase the stability of DNA?
The backbone protects the more chemically reactive organic bases within the helix
How are the base pairs involved in the stability of DNA?
More C-G pairs = more stability because they form 3 hydrogen bonds whereas A-T pairs form 2
What is the function of DNA?
Passes genetic information from cell to cell and through generations and provides genetic diversity in organisms due to variety in ACGT sequences
How does the stability of DNA benefit the practical world?
It only rarely mutates due to its stable structure
How are protein synthesis and DNA replication made easier by DNA’s structure?
The two strands can separate easily as they are only joined by hydrogen bonds
How does DNA being a large molecule benefit?
It is able to carry lots of genetic information
How are the inner base pairs of DNA protected from corruption by chemical and physical forces?
The sugar-phosphate backbone is somewhat protecting them
Explain why semi-conservative DNA replication is so named
In each new DNA molecule, half of it is from the original/parental copy
Why is it important to retain one original strand of DNA?
Ensures genetic continuity between generations and new cells produced inherit all their genes from their parent cells. Important because our cells are regularly replaced so new ones need to be the same as old ones
When does the process of DNA replication take place?
The S phase (interphase)
What is helicase and what does it do?
An enzyme that unwinds the helix by breaking the hydrogen bonds between base pairs to form 2 separate polynucleotide chains which act as templates for the formation of new strands
What is DNA polymerase and what does it do?
An enzyme that catalyses the joining of new nucleotides (condensation reaction) to form a new strand of DNA
How do two strands of RNA form a new DNA molecule?
Hydrogen bonds form between complementary base pairs
Describe the results of one replication of DNA during conservative replication
Produces one entirely new DNA double helix made of 2 new strands and one double helix which has both old strands
Describe the results of one replication of DNA during dispersive replication
produces 2 double helices both containing distinct regions of DNA composed of either both old DNA or both new DNA
Describe the results of one replication of DNA during semi-conservative replication
produces 2 double helices, each with one original strand and one new strand
How can we prove that semi-conservative replication takes place?
As DNA is made up of nitrogen bases, the two isotopes of nitrogen (14 and 15) can be used
Describe the process of how semi-conservative DNA replication is proven
- Bacterial DNA (E coli) is placed in media of ¹⁵N which binds to DNA
- Bacteria is moved to media of ¹⁴N and is left to replicate once
- DNA is put in a test tube of caesium chloride and centrifuged at 40 000 revs/hr
- Caesium chloride sinks to the bottom, creates a conc. gradient and DNA moves to its corresponding level
Why is caesium chloride used when centrifuging DNA specimens to prove semi-conservative replication?
It is a heavy compound so creates a concentration gradient for the DNA to move through
How is the test tube observed after centrifuging it during the proof of semi-conservative DNA replication?
Observed under UV rays. DNA appears as a fine layer in the test tube at different heights based on density
Why is it inaccurate to say that Watson and Crick discovered the structure of DNA?
- Rosalind Franklin first discovered helical structure of DNA
- Watson’s sister somewhat spied on Linus Pauling via dating his son
- Crick uses other people’s ideas and never credits them when he steals them
What is an ATP molecule made up of?
3 phosphate groups, a ribose and an adenine base
What is produced after ATP is hydrolysed?
An inorganic phosphate group, a ADP molecule and energy
What does ATP stand for?
Adenosine triphosphate
What does ADP stand for?
Adenosine diphosphate
Which enzyme catalyses the hydrolysis of ATP?
ATP hydrolase
Which enzyme catalyses the condensation of ADP and Pi?
ATP synthase
What does the synthesis of ATP require and where does it occur?
Requires energy
Occurs in:
- cytoplasm by glycolysis
- mitochondria during aerobic respiration
- chloroplasts by photsynthesis
How is energy within ATP and how is it released?
The bonds between phosphate groups are unstable so they have a low activation energy. Therefore they are easily broken and energy is released when they are broken
Why is ATP an immediate energy source of cells?
It’s not a good long-term energy source because of the unstable bonds between phosphate groups. Cells don’t contain a lot of ATP (just a few seconds’ worth) which isn’t a problem as ATP is rapidly reformed
What reasons are there for why ATP is a better immediate energy source then glucose?
- Each ATP molecule releases less energy than each glucose molecule so the energy is more manageable
- Hydrolysis of ATP into ADP is a single reaction that releases immediate energy whereas glucose breakdown takes much longer
Is ATP stored or made? Explain
ATP can’t be stored and so is continuously made by the mitochondria
Where is there lots of mitochondria and for what purpose?
In muscle cells and epithelial cells of small intestine for muscle contraction and active transport
What processes is ATP required for?
- metabolic processes
- movement
- active transport
- secretion
- activation of molecules
Explain why metabolic processes need ATP
Need energy for build up of macromolecules eg. polypeptides from amino acids
Explain why movement needs ATP
Energy is needed for muscle contraction. ATP provides energy for filaments of muscle to slide over one another and shorten muscle length
Explain why active transport needs ATP
Energy is needed to change the shape of carrier proteins to allow molecules/ions to move against concentration gradient
Explain why secretion needs ATP
Energy to form and move lysosomes
Explain why activation of molecules needs ATP
Phosphate released from ATP and phosphorylate compounds to make them more reactive by lowering their activation energy
Why is water a polar molecule?
The sharing of electrons is uneven in molecules. Weak negative region on oxygen atom and weak positive areas on hydrogen atoms
What is another way of saying water is a polar molecule?
Water has a permanent dipole
What properties of water are caused by the hydrogen bonding between H2O molecules?
- excellent solvent
- high specific heat capacity
- high latent heat of vaporisation
- less dense as a solid
- high surface tension + cohesion (sticks to itself and forms droplets)
- high adhesion (sticks to other things)
- acts as a reagent
Explain how water is a good solvent
- polar substance so many ions and other covalently bonded polar substances will dissolve in it
- dissolved solutes are more reactive in solution so allows reactions to occur in cells
- metabolites can be transported more efficiently
Explain how it is good that water has a high specific heat capacity
- it takes a lot of energy to fluctuate the temperature of water
- provides suitable habitats
- enzyme activity isn’t affected as temp of environment doesn’t fluctuate
- water in blood plasma is able to transfer heat round the body
Explain how it is good that water has a high latent heat of vaporisation
- takes lots of energy to break hydrogen bonds and evaporate
- acts as a coolant in living organisms
Explain how it is good that water has the properties of cohesion and adhesion
- strong cohesion and adhesion allows water to move through xylem and blood vessels and enables surface tension so insects (eg. pond skaters) can float
- adhesion is water hydrogen bonding to other molecules eg. cellulose
What is an inorganic ion?
An ion not containing carbon
Where do inorganic ions occur in the body?
In solution in cytoplasm and body fluids. Some concentrations are low, some are high and some fluctuate. Some inorganic ions are used in cell signalling and nervous transmission
