Biology AS level Flashcards
What dose ATP stand for?
Adenosine triphosphate
What do all eukaryotic cells contain?
All eukaryotic cells contain a nucleus and membrane bound organelles
What is a virus?
Viruses are non-cellular and are parasitic as they reproduce by infecting and taking over living cells. The virus DNA/ RNA hijacks the protein synthesising machinery of the host cell, which then helps to make new viral proteins to make capsid.
Define eukaryotic cells
Eukaryote cells are organisms with a true nucleus and have membrane bound organelles e.g. animals, plants, fungi, protoctist. They contain membrane bound organelles and a nucleus, and their ribosomes are smaller (70S)
Define prokaryotic cells
Prokaryote cells are organisms that lack a nucleus and have simpler structure e.g. bacteria. They contain membrane bound organelles, a nucleus and ribosomes in the cytoplasm of eukaryotic cells (80S)
What is plasmodesmata?
- Plasmodesmata are pore-like structures found in cell walls that allow a link between neighbouring cells by fine threads of cytoplasm.
- They are small channels that pass through the cell wall of adjoining plant cells to allow communication between cells.
What do prokaryotic cells such as bacteria contain?
● Cell wall – Rigid outer covering made of peptidoglycan
● Capsule – Protective slimy layer which helps the cell to
retain moisture and adhere to surfaces
● Plasmid –Circular piece of DNA
● Flagellum- a tail like structure which rotates to move the cell
● Pili- Hair-like structures which attach to other bacterial cells
● Ribosomes- Site of protein production
● Mesosomes- Infoldings of the inner membrane which contain enzymes required for respiration
What is a virus structure?
Viruses are non-living structures which consist of nucleic acid (either DNA or RNA) enclosed in a protective protein coat called the capsid, sometimes covered with a lipid layer called the envelope.
What is a cell wall and state its features?
- A cell wall is rigid as it contains fibres of cellulose (polysaccharide).
- Cell walls give the cell its definite shape and prevents it from bursting (by osmosis), allowing turgidity.
- May be reinforced by lignin for extra strength.
- Freely permeable.
Where is chloroplast found?
Chloroplasts is a cell structure that is only found in plant cells in the palisade mesophyll, spongy mesophyll and surface of stem which carries out photosynthesis and ATP synthesis.
It has a double membrane and contains flattened sacs known as thylakoids.
What are the feature of chloroplast?
- Chlorophyll is embedded in thylakoid membranes.
- Thylakoids stacked on top of each other to form grana.
- Grana are linked by lamella. These structures are present in a matrix called the stroma.
- Contains starch grains, circular DNA and 70S ribosomes.
What is a ultrastructure?
A more detailed structure of cells that can be obtained by using a microscope
What are the features of a generalised plant cell?
- Chloroplasts (5-10μm)
- Cell wall (10 nm)
- Plasmodesmata
- Large vacuole and tonoplast
What is the endosymbiont thoery?
Endosymbiont theory states that mitochondrion and chloroplast were bacteria that now live inside larger cells of animals and plants, which is why chloroplast and mitochondrion have circular DNA.
What is the role of ATP?
- ATP is made up of 3 phosphate groups, a nitrogenous base and a ribose sugar.
- Energy is released when ATP is hydrolysed to form ADP and a phosphate molecule. This process is catalysed by ATP hydrolase.
- The inorganic phosphate can be used to phosphorylate other compounds, as a
result making them more reactive. - Condensation of ADP and inorganic phosphate catalysed by ATP synthase produces ATP during photosynthesis and respiration.
What is ATP?
It is the energy carrying molecule produced in mitochondria that spreads to parts where needed.
Energy is released by breaking ATP to ADP, a reversible hydrolysis reaction.
What happens in electron microscope?
- Very small particles can be observed as the electrons are easily absorbed.
- The parts of the specimen that appear darker in the final image are denser and absorb more electrons.
- Due to higher resolution, the electron micrographs of plant and animal cells show most organelles.
- Vacuum present in EM to prevent electrons from colliding with air particles to gain a sharp image.
- Water boils in RT in a vacuum, so specimen should be dead.
What is the difference between magnification and resolution?
Magnification is an indicator of how much bigger the microscope imagine is than the actual object whereas
resolution is the smallest interval measurable by a microscope. Magnification depends on the power of the objective and eyepiece lens used, while with resolution the higher of detail that can be seen the higher resolution
How do you calculate magnification?
Magnification can be calculated by dividing the size of the image by the size of real object.
What is an eyepiece graticule and how is it used?
- An Eyepiece graticule is fitted into the eyepiece of the microscope and is used to measure objects.
- Has no units and is calibrated by the stage micrometre which has an accurate scale (in mm) and provides reference dimensions.
1mm= 1000 μm
1μm= 1000 nm - Use the same magnification when calibrating the eyepiece graticule and when using it to measure the specimen.
What is the relationship of resolution and wavelength?
- Limit of resolution: half the wavelength of radiation used to view specimen.
- Electrons have extremely short wavelength.
- They’re negatively charged, thus easily focused using electromagnets.
- Light microscopes resolution is 200nm and wavelength is 400-700nm
- electron microscope resolution is 0.1-0.5nm its wavelength is ±0.005nm
what is one millimetre in micrometre?
What is one micrometre in nanometre?
1mm= 1000 μm
1μm= 1000 nm
What is an organelles?
Organelles is a functionally and structurally distinct part of a cell, usually membrane bound.
What is a cell surface membrane?
Cell surface membrane is a selectively permeable membrane in plant and animal cells that allows for the exchange of certain biological molecules and ions. It surrounds the cell and controls what enters and exits
- Extremely thin with trilaminar appearance
- It is comprised of phospholipid bilayers which are assembled with the hydrophilic phosphate heads facing the aqueous environment (inside and outside the cell) and the hydrophobic tails facing each other.
What is the function of a cell surface membrane?
- Barrier between cytoplasm and external environment
- Cell signalling
- Cell recognition (surface antigens)
- Cell-to-cell adhesion
- Site for enzyme catalysed reactions
- Anchoring the cytoskeleton
- Selection of substances that enter/leave the cell
- Formation of Hydrogen bonds with water for stability
What is the nucleus?
Nucleus is the largest organelle surrounded by the double membraned nuclear envelope and is continuous with rough endoplasmic reticulum.
It is surrounded by a double membrane called the envelope containing pores which enable molecules to enter and leave the nucleus, the nucleus also contains chromatin and a nucleolus which is the site of ribosome production.
What is a nucleor pore and its functions?
Nuclear pore are gaps in the nuclear envelope that allow exchange between the nucleus and cytoplasm.
- Substances leaving: mRNA and ribosomes for protein synthesis.
- Substances entering: protein to help make ribosome, nucleotide, ATP, & some hormones
What do chromosomes contain?
Chromosomes contain the hereditary material DNA that is organised into genes which controls the activities of the cell and inheritance.
What is the rough endoplasmic reticulum?
Rough endoplasmic reticulum (RER) is an extensive membrane system with 80S ribosomes are sites for protein synthesis which produce the rough appearance.
RER folds and processes proteins made on the ribosomes
What is the function of RER?
- The R.E.R provides a pathway for transport of materials through cell.
- Forms a complex 3D system of sheet like membranes and tubes enclosing fluid-filled sacs.
- Proteins made by ribosomes on RER enter sacs and move through them.
- Transport vesicles bud off from the RER and join forming the Golgi body.
What is smooth endoplasmic reticulum?
Smooth Endoplasmic reticulum is a system of membrane bound sacs these are a site for lipid synthesis and steroids e.g. cholesterol and reproductive hormones.
the system is a meshwork of tubular membrane vesicles with fluid filled sacs that have no ribosome on its surface
What are the features of a Golgi body/complex/apparatus?
- Golgi body/complex/apparatus is a stack of flattened membranes enclosing hollow sacs (cisternae) formed by transport vesicles which bud off of the RER, and are broken down to form Golgi vesicles.
- It collects, processes, modifies and sorts molecules that are ready for transport in Golgi vesicles to other parts of the cell or out of the cell by secretion/exocytosis
- Makes lysosomes, glycoproteins and functioning proteins.
What is the Golgi body/complex/apparatus?
Golgi apparatus is a series of fluid filled, flattened & curved sacs with vesicles surrounding the edges. The Golgi apparatus processes and packages proteins and lipids. It also produces lysosomes.
What is secretion/exocytosis in the Golgi body/complex/apparatus?
secretion/exocytosis is the fusion of vesicle with plasma membrane to release content.
What dose mitochondria contain?
Mitochondria are usually oval shaped, bound by a double membrane called the envelope. The inner membrane is folded to form projections called cristae with matrix on the inside containing all the enzymes needed for respiration
What are the features of mitochondria?
- Has a matrix that contains 70S ribosomes and circular DNA which is used to make some of the mitochondrion’s own proteins.
- Cristae: folding of inner membrane that projects into interior solution, matrix.
- Intermembrane space: space between the two membranes.
- Porin: transport protein in outer membrane, forms wide aqueous channel allowing water-soluble molecules from cytoplasm to intermembrane space.
- Inner membrane: selective barrier controlling entrance of ions and molecules into the matrix.
What is mitochondria?
Mitochondria surrounded by mitochondrial envelope; provides energy for aerobic respiration, synthesizes lipids and is more in areas that require maximal energy.
What is ribosomes?
Ribosomes are the site at which mRNA (transcribed from the nucleus) is translated into polypeptides with the help of tRNA, therefore help with protein synthesis. They are not membrane bound and are made up of rRNA and rProteins.
Ribosomes are composed of two sub units and are the site of protein production
What are ribosomes two sub units an?
- Small subunit: site of translation (mRNA binds here and is read by this unit)
- Large subunit: joins amino acids to form polypeptide.
What is the 70S and 80S ribosomes found?
- 80S ribosomes: in the cytoplasm and R.E.R
- 70S ribosomes: in chloroplast and mitochondria.
What are lysosomes?
- Lysosomes are a single membrane with no internal structure in animal cells. They contain digestive (hydrolytic) enzymes bound by a single membrane that’s kept separate from rest of cell to prevent damage.
- They are responsible for breakdown of unwanted structures e.g. old organelles or whole cells, in WBC to digest bacteria.
What are microtubules?
Microtubules are long hollow tubes that make up the cytoskeleton which helps determine cell shape.
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How is microtubules made?
- Made up of alpha and beta tubulin that combine to form dimers.
- Dimers join end to end to form protofilaments (polymerisation).
- 13 protofilaments line up alongside each other in a ring to form a cylinder with a hollow center i.e. microtubule.
- Forms an intracellular transport system by moving along secretary vesicles, organelles and cell components on its outer surface
What is centriole?
- Centriole are formed by 9 triplets of microtubules. - — Microtubules extend from centriole and attach themselves to kinetochore of chromosomes, forming spindle fibres.
- Centrioles duplicate, and a pair of centrioles then move to opposite poles of the cell (2 centrosome regions), thus separating sister chromatids during nuclear division.
- Centrioles at bases of cilia and flagella (basal bodies) act as MTOCs. Microtubules extending from basal bodies into cilia and flagella help with their beating movements.
What is a vaculoe?
The vacuole is a fluid-filled sac present in plant cells, surrounded by a membrane called the tonoplast. It contains mineral salts, sugars, amino acids, waste substances and pigments. Its role is to colour the cell to attract pollinating insects, act as a temporary food store and provide support through turgidity
What are the features of a generalised animal cell?
- Cell surface membrane
- Nucleus
- Endoplasmic reticulum
- Mitochondria
- Ribosomes
- Lysosomes
- Microtubules
- Centrosome
- Centriole
What are the features of a generalised plant cell?
- Cell surface membrane
- Nucleus
- Endoplasmic reticulum
- Mitochondria
- Ribosomes
- Lysosomes
- Microtubules
- Centrosome
- Centriole
- Chloroplasts
- Cell wall
- Plasmodesmata
- Large vacuole and tonoplast
What do plants and animal cells have in common?
- Cell membrane
- Nucleus
- Cytoplasm
- Mitochondria
- Golgi apparatus
What is the cell shape of a plant cell and an animal cell?
Animal cells look spherical while plant cells look rectangular
What is special about mitochondria and cytoplasm?
They both make ATP, which the energy currency of the cell
What are the differences between a prokaryotes and eukaryotes?
- The DNA in prokaryotes is circular and lies free in the cytoplasm. It is naked
- The DNA in eukaryotes is non circular, contains a nucleus
- In prokaryotes there are very few organelles none which are membrane bound
- In eukaryotes there are many organelles, some single bound, some double-bound and some have no membrane
- In eukaryotes ER is present and maybe attached to ribosomes
- In prokaryotes the cell wall contains murein
- In eukaryotes the cell wall when present contains cellulose or lignin in plants and chitin in fungi
- In prokaryotes their are no ER
- In prokaryotes the Ribosomes are 70s
- In eukaryotes the ribosomes are 80s
What is benedict’s test for reducing sugars?
Equal volume of sample being tested and Benedict’s solution are mixed and heated in a water bath up to 95C.
Positive: green → yellow → orange → brick red
Negative: blue
What dose benedict solution test for?
Benedict’s solution can be used to test for the presence of reducing sugars. Reducing sugars include all monosaccharides and some disaccharides. Therefore it
can be used to test for glucose, fructose and maltose.
It does not test for sucrose, however the test involves heating the sugar with Benedict’s solution – if the colour
changes from blue to brick red then glucose is present.
What is the benedict’s test for non-reducing sugars?
If there is no colour change after caring out benedict’s solution it could be that there is a non-reducing sugar
present (e.g. sucrose). You can break the glyosidic bonds by acid hydrolysis.
1. Add dilute Hydrochloric acid (catalyst) to the test solution in the ratio of 1:2 and heat in a water bath. . respectively approximately 2 minutes.
2. A pinch of sodium hydroxide is added to make the solution alkaline therefore neutralising it
3. Heat with Benedict’s solution
How do you carry out Benedict test semi-quantitatively?
- You can do this by measuring the time it takes for the colour change to happen. The different times can help estimate the concentration.
- You could also use the different colour changes and work out the concentration of glucose using colorimetry.
- Higher glucose concentration means lower absorbance of the solution
1. Do Benedict’s test
2. Calibrate colorimeter with plain water and use this as your control
3. Remove precipitates from each test tube by using a centrifuge
4. Measure the absorbance using a colorimeter
5. Create a calibration curve of concentration of glucose vs absorbance (this can be used to find glucose concentrations of different unknowns)
How do you do the biuret test?
Biuret’s test used to detect the presence of proteins: Equal amounts of the sample and Biuret’s solution are added together, giving purple colour over several minutes in the presence of proteins, and blue in its absence.
How do you test for the presence of proteins?
You use biuret test
How do you do an emulsion test?
Emulsion test for lipids: The sample is added to 2cm3 of ethanol and mixed well until it dissolves (lipids are soluble in ethanol). This mixture is then placed into a test tube containing the same amount of water. A milky white emulsion will appear if lipids are present and remain clear if not.
How do you test for lipids?
You use the emulsion test
How do you test for sugars?
You use the benedict’s test
How do you do the iodine test?
Iodine test for the presence of starch: Iodine solution is orange-brown. Add a drop of iodine solution to the solid or liquid substance to be tested. A blue-black colour is quickly produced if starch is present.
How do you test for the presence of starch?
You use the iodine test
What are carbohydrates?
Carbohydrates are molecules which consist only of carbon, hydrogen and oxygen and they are long chains of sugar units called saccharides
What are the different types of saccharides?
There are three types of saccharides monosaccharides, disaccharides and polysaccharides.
What is glucose?
Glucose is a monosaccharide containing six carbon atoms in each molecule, it is the main substrate for
respiration and the energy source which is broken down during respiration therefore it is of great importance. It has two isomers – α- glucose and β - glucose and their difference lies between the position of an –OH group in their ring structures.
What is glucose molecular formula?
Glucose has the molecular formula C6H12O6.
What is the monomer form which starch and cellulose are made
Glucose is the monomer from which Starch and Cellulose are made
What is a monomer?
A monomer simple molecule which is used as a basic building block for the synthesis of a polymer; many monomers are joined together to make the polymer, usually by condensation reactions e.g. monosaccharides, amino acids, nucleotide.
What is a polymer?
A polymer: is a giant molecule made from monomers e.g. polysaccharides, proteins, nucleic acids
What is a macromolecule?
A macromolecule are large and complex molecules that are formed due to polymerisation of smaller monomers e.g. polysaccharides, nucleic acids
Define monosaccharide
Monosaccharide is a molecule consisting a single sugar unit, the simplest form of carbohydrate and cannot be hydrolysed further. It has a general formula of (CH2O)n.
What is a monosaccharide ?
Monosaccharides are small organic molecules used as building blocks of complex carbohydrates. Monosaccharides have a varying number of carbon atoms, for instance:
- Glyceraldehyde is a triose used in metabolic reactions
- Ribose is a pentose sugar which is a component of nucleic acid
- Glucose is a monosaccharide which is the substrate for respiration
Define disaccharide
Disaccharide is a sugar molecule consisting of two monosaccharides joined together by a glycosidic bond.
How are disaccharides formed and state some examples
Disaccharides are formed in a condensation reaction between two monosaccharides.
- Maltose is a disaccharide formed by condensation of two glucose molecules
- Sucrose is a disaccharide formed by condensation of glucose & fructose
- Lactose is a disaccharide formed by condensation of glucose & galactose
Define polysaccharide
Polysaccharide is a polymer whose subunits are monosaccharides joined together by glycosidic bonds.
Give an example of some polysaccharides
Polysaccharides include:
- Glycogen and starch which are both formed by the condensation of alpha glucose
- Cellulose formed by the condensation of beta glucose
Define glycosidic bonds
Glyosidic bonds are covalent bonds that occur between constituent monomers and are formed due to a condensation reaction which involves the removal of a water molecule in order to form polysaccharides and disaccharides such as sucrose.
How can glycosidic bonds be separated?
Constituent molecules in glyosidic bonds can also be separated by hydrolysis which breaks the glycosidic bond between monomers e.g.: Acid hydrolysis of non-reducing sugars (sucrose) breaks glycosidic bond in order to retrieve constituent monomers
What is starch?
Starch is a macromolecule that is found in plant cells. Starch is highly compact and stores energy.
What is starch made up of?
Starch is made up of two components known as amylose and amylopectin. These components are polysaccharides that are made from a glucose molecules and contain 1,4 glycosidic bonds
What is amylose?
Amylose is an unbranched chain of glucose molecules joined by α 1,4 glycosidic bonds, as a result of that amylose is coiled and thus it is a very compact
molecule meaning it can store a lot of energy in a small space.
What is amylopectin?
Amylopectin is branched and is made up of glucose molecules joined by α 1,4 and 1,6 glycosidic bonds, due to the presence of many side branches it is rapidly digested by enzymes therefore energy is released quickly.
What is glycogen?
Glycogen is a macromolecule that is the main energy storage molecule in animals and is also made from α glucose molecules. The structure of glycogen is very similar to that of amylopectin; however, it is more branched and therefore contains more α 1,6 glycosidic bonds and therefore energy can be released quickly. Moreover, it is a relatively large but compact molecule thus maximising the amount of energy it can store
What is cellulose?
Cellulose is found in the cell wall of plant cells and is made from long unbranched chains of β-glucose units that form β-1,4 glycosidic bonds. Alternate β- glucose molecules are rotated 180 degrees in order to form these bonds.
What is microfibres?
- Hydrogen bonds are also formed between parallel cellulose molecules. 60 and 70 cellulose molecules become tightly cross-linked to form bundles called microfibrils. Microfibrils are in turn held together in bundles called fibres by hydrogen bonding.
- Fibres increase tensile strength to withstand osmotic pressure, making the plant rigid and determine cell shape. They’re also freely permeable…
What are triglycerides?
Triglyceride are forms by the condensation of 3 fatty acid chains and 1 glycerol molecule, joined by an ester bond formed in condensation. Triglycerides are non-polar and hydrophobic molecules.
Triglycerides are used as energy reserves in plant and animal cells.
What are fatty acid chains?
Fatty acid chains are long hydrocarbon chains with a carboxylic head.
What is glycerol?
Glycerol is an alcohol containing 3 OH groups.
What is glycerol?
Glycerol is an alcohol containing 3 OH groups.
What is glycerol?
Glycerol is an alcohol containing 3 OH groups.
What is a unsaturated fatty acid?
-Unsaturated fatty acids contain c=c bonds that are easier to break and melt easily. More than one c=c is a polyunsaturated fatty acid.
What is a saturated fatty acid?
Saturated fatty acids contain c-c bonds that are solids at room temperature.
What is the role of a triglyceride?
- Better energy reserves than carbohydrates as more CH bonds
- Acts as an insulator and provides buoyancy
- A metabolic source of water as gives CO2 and H20 on oxidation in respiration
What is the difference in triglyceride and phospholipid structures?
In phospholipids, one of the fatty acids of a triglyceride is substituted by a phosphate-containing group
What is the structure of a phospholipid?
In a phospholipid the hydrophilic head contains a phosphate group and glycerol while the hydrophobic tail contains 2 fatty acid chains. This is due to the partial negative charge on the phosphate group that gets attracted to the partial positive charge on the hydrogen atom of the water molecule.
What happens when phospholipids are in contact with water?
Phosphate heads are hydrophilic and the tails are
hydrophobic and as a result phospholipids form micelles when they are in contact with water as heads are on the outside as they are attracted to water and tails are on the inside as they move away from water.
What makes cell membranes selectively membrane?
The hydrophobic/hydrophilic nature of phospholipids is
what makes cell membranes selectively membrane
What are proteins?
Proteins are made of amino acids which only differ in the R- groups/ variable side chains and will always contain an amine group (basic), carboxyl group (acidic) and a hydrogen atom attached to the central carbon atom.
How are amino acids joined and formed?
Amino acids are joined by peptide bonds formed in
condensation reactions.
What is an amino acid?
Amino acids are the monomers from which proteins
are made.
Amino acids contain an amino group –NH2, carboxylic acid group and a variable R group which is a carbon-containing chain. There are 20 different amino acids with different R groups.
What are the difference between dipeptide and polypeptide?
A dipeptide contains two amino acids and polypeptides contain three or more amino acids.
How is a peptide bond formed and broken?
- A peptide bond is formed by condensation between 2 amino acids, forming a dipeptide. Many amino acids that join together by peptide bonds form a polypeptide.
- Peptide bonds are broken when hydrolysed into amino acids, often occurring in the small intestine and stomach.
What is the structure of a protein determined?
The structure of proteins is determined by the order and number of amino acids, bonding present and the shape of the protein.
What is the primary structure of a protein?
Primary structure is a sequence of amino acids in a polypeptide/protein. A slight change in the sequence of amino acids can affect the protein’s structure and function. It has a unique sequence for each protein.
What is a secondary structure of a protein?
Secondary structure is the structure of a protein molecule resulting from the regular coiling or folding of the chain of amino acids. The secondary structure is the shape that the chain of amino acids chains – either alpha helix or beta pleated sheet. The type of bond determines the shape
What are the shape of the secondary structure by hydrogen bonding?
Hydrogen bonding - weak bonds between a slightly positively-charged hydrogen atom and another slightly negatively-charged atom (usually nitrogen, oxygen or fluorine).
What is the ionic bond of the tertiary structure of a protein?
Ionic bond - attraction between oppositely charged R groups
What is the disulphide bridge a of tertiary structure of protein?
Disulphide bridges - when 2 cysteine amino acids come into close contact and the sulfur in each cysteine forms a bond.
What is the alpha helix in a secondary structure?
α- helix: the polypeptide chain twists into a regular spiral and is maintained by hydrogen bonds between the (-NH) group of one amino acid and the (CO-) group of another amino acid 4 spaces later in the polypeptide chain.
What dose the beta helix sheet do in the secondary structure?
β- pleated sheet: the chain is not tightly coiled and lies in a looser, straighter shape.
What is the tertiary structure in a protein?
Tertiary structure is the compact structure of a protein molecule resulting from the three-dimensional coiling of the already-folded chain of amino acids. It can be globular or fibrous.
What are the different bonds and interactions that make a tertiary structure and how can they be broken?
- Hydrogen bonds between wide varieties of R- groups (can be broken by PH and temperature changes)
- Disulphide bridges between two cysteine molecules (can be broken by reducing agents)
- Ionic bonds between R groups containing amine and carboxyl groups. (Can be broken by PH changes.)
- Hydrophobic interactions between non polar R groups.
What are globular protein?
Globular proteins curl up into a spherical shape with their hydrophobic regions pointing into the centre of the molecule and hydrophilic regions pointing outwards. They are soluble in water e.g. enzymes and haemoglobin.
What are fibrous proteins?
Fibrous proteins: form long strands, are insoluble in water, and have structural roles e.g. collagen, hair, nails.
What is the quaternary structure of a protein?
Quaternary structure is the three-dimensional arrangement of two or more polypeptides, or of a polypeptide and a non-protein component such as haem, in a protein molecule closely packed together. The polypeptide chains are held together by bonds in the tertiary structure.
What is haemoglobin and what is it structure?
Haemoglobin is a globular protein that has a quaternary structure with 4 polypeptide chains, 2 α-globin and 2 β-globin chains. Each chain has one prosthetic (non-protein) group - haem (Fe2+). containing an iron atom that reversibly binds to an oxygen molecule. Oxyhaemoglobin is bright red, when the haem group is combined with oxygen, otherwise it’s purplish.
What is sickle cell anaemia?
Sickle cell anaemia is a genetic condition in which a polar amino acid, glutamic acid is substituted by non-polar valine on the surface of the β chain in haemoglobin, making it less soluble.
What is collagen?
Collagen is a fibrous protein that is present in the skin, bones, teeth, cartilage and walls of blood vessels. It is an important structural protein.
What is the structure of collagen?
- A collagen molecule has 3 polypeptide chains that are coiled in the shape of a stretched-out helix.
- Compact structure and almost every 3rd amino acid is glycine, the smallest amino acid which can form H-bonds.
- 3 polypeptide strands are held together by hydrogen and covalent bonds.
- Many of these collagen molecules lie side by side, linked to each other by covalent cross-links between the side chains of amino acids, forming fibrils, and many fibrils make up a fibre.
What is the structure of collagen?
- A collagen molecule has 3 polypeptide chains that are coiled in the shape of a stretched-out helix.
- Compact structure and almost every 3rd amino acid is glycine, the smallest amino acid which can form H-bonds.
- 3 polypeptide strands are held together by hydrogen and covalent bonds.
- Many of these collagen molecules lie side by side, linked to each other by covalent cross-links between the side chains of amino acids, forming fibrils, and many fibrils make up a fibre.
How is water held together?
A water molecule contains two hydrogen atoms and one oxygen atom held together by hydrogen bonds.
Why is water an effective solvent?
Water is an effective solvent because of its polarity and so can form electrostatic interactions with other polar molecules and ions. Thus it’s a transport medium and reagent for metabolic and other reactions in the cells of plants and animals.
When is water a metabolite?
It is a metabolite in metabolic reactions such as condensation and hydrolysis which are used in forming and breaking of chemical bonds
What is cohesion and tension in water?
High surface tension and cohesion: cohesion refers to the attraction of one water molecule to the other. Water molecules have strong cohesive forces due to hydrogen bonds, thus having high surface tension. As a result of strong cohesion the surface tension at the water-air boundary is high
What is specific heat capacity?
Specific heat capacity is the amount of heat energy required to raise the temperature of 1 kg of water by 1 °C.
Why dose water have a high specific heat capacity?
Water has high specific heat capacity due to its hydrogen bonds. Temperature within organisms remains constant compared to external temperature, and water bodies also have a slow change in temperature, providing stable aquatic habitats. A lot of energy is required to warm water up therefore minimising temperature fluctuations in living things therefore it acts as a buffer.
What is latent heat of vaporization?
latent heat of vaporization is the measure of the heat energy needed to vaporise a liquid.
Why does water have a high latent heat of vaporization?
Water has a high latent heat of vaporization due to its high specific heat capacity as H bonds need to be broken before water can be vaporised, cooling the surrounding environment. Sweating is a good cooling mechanism. However, a large amount of energy can be lost for little amount of water, thus dehydration is prevented e.g. in transpiration.
What are the density and freezing properties of water?
Ice is less dense than water and floats on it, insulating water and preventing it from freezing, preserving aquatic life underneath it. Changes in the density of water with temperature cause currents, which help to maintain the circulation of nutrients in the oceans.
What is the differnece in stuructre of alpha and beta glucose?
In beta glucose the OH molecule is above the ring and with alpha glucose the OH molecule is below the ring
What is the differnece in stuructre of alpha and beta glucose?
In beta glucose the OH molecule is above the ring and with alpha glucose the OH molecule is below the ring
What is the difference in structure of alpha and beta glucose?
In beta glucose the OH molecule is above the ring and with alpha glucose the OH molecule is below the ring
Define enzyme
An enzyme is a biological catalyst that accelerates metabolic reactions. Enzymes are globular proteins as they have a roughly spherical shape and are water soluble. They increase the rate of reaction by lowering the activation energy of the reaction they catalyse. Each enzyme has a specific shape that must be complementary to the substrate
Define enzyme
An enzyme is a biological catalyst that accelerates metabolic reactions. Enzymes are globular proteins as they have a roughly spherical shape and are water soluble. Enzymes increase the rate of reaction by lowering the activation energy. Each enzyme has a specific shape that must be
complementary to the substrate
Define enzyme
An enzyme is a biological catalyst that accelerates metabolic reactions. Enzymes are globular proteins as they have a roughly spherical shape and are water soluble. Enzymes functioning inside a cell are intracellular, but those that are secreted by cells and catalyse reactions outside cells are described as extracellular.
What is an active site of an enzyme?
The active site is the area of the enzyme where the
reaction with the substrate takes place. Each enzyme has a specific shape that must be complementary to the substrate, meaning that only one type of substrate fits into the active site of each enzyme. Enzymes have specific active sites that are complementary to the shape of the substrate.
What is the enzyme-substrate complex?
The substrate is held in place at the active site by weak hydrogen and ionic bonds. The combined structure is called the enzyme-substrate complex.
What is the induced fit model?
When the enzyme and substrate form a complex, the structure of the enzyme is altered so that the active site of the enzyme fits around the substrate. This is called the induced fit model.
What is the lock and key theory and who was it proposed by?
Proposed by Fischer in 1894
- Active site and substrate have complementary shapes prior to binding
- The enzyme binds with substrate forming an enzyme-substrate complex
- Products are released from active site and enzyme can be reused
- Only one substrate can fit each active site
- The enzyme-substrate complexes formed enable the reaction to take place more easily.
What is activation energy?
Activation energy is the energy required in any chemical reaction to break the bonds in reactant molecules so that new bonds are formed to make the product. An enzyme lowers the activation energy required for the reaction. However, overall energy released during reaction is maintained
What is the induced fit theory and who was it proposed by?
Proposed by Koshland in 1958
- Enzyme has active site that is not initially an exact fit to the substrate molecule.
- Enzyme is moulded around substrate as it enters to become complementary forming an enzyme-substrate complex
- Bonds form between oppositely charged groups on substrate and R groups to induce a better fit. This puts a strain on the substrate molecule so reactions occur more easily.
How can the effect of enzymes be measured on the rate of reactions
- By measuring the amount of product accumulated over a period of time. Rate of reaction = volume of product produced / time. E.g. enzyme catalase breaking hydrogen peroxide to H2O + o2
- By measuring the rate at which the reactants disappear from the reaction mixture, the effect of the enzyme on the rate of reaction can be determined.
E.g.: measuring the rate at which starch disappears when the enzyme amylase is added.
How can you investigate enzyme activity over a period of time using a catalase?
- Catalyses the breakdown of hydrogen peroxide
- Products: oxygen and water
- Measure the rate of oxygen produced over a period of time
- You can plot a graph of time vs volume of oxygen produced
How can you investigate enzyme activity over a period of time using amylase?
- Catalyses the breakdown of starch
- Products: maltose
- Amylase is added to the starch samples
- At regular timed intervals take samples
- Use iodine/KI solution to test for the presence of starch (colour change to orange-brown when starch breakdown is complete)
- Measure the absorbance in a colorimeter (make sure colorimeter is calibrated and sample has been mixed properly with the iodine)
- The darker the colour the higher the starch concentration hence a higher absorbance
- Plot a graph of time vs absorbance
How can you investigate enzyme activity over a period of time using amylase?
- Catalyses the breakdown of starch
- Products: maltose
- Amylase is added to the starch samples
- At regular timed intervals take samples
- Use iodine/KI solution to test for the presence of starch (colour change to orange-brown when starch breakdown is complete)
- Measure the absorbance in a colorimeter (make sure colorimeter is calibrated and sample has been mixed properly with the iodine)
- The darker the colour the higher the starch concentration hence a higher absorbance
- Plot a graph of time vs absorbance
Why is the rate of an enzyme reaction faster at the beginning?
Initially, there’s a large number of substrates and every enzyme has a substrate in its active site. The rate at which the reaction occurs depends only on how many enzymes there are and the speed at which the enzyme can convert the substrate into product, release it, and then bind with another substrate. However, overtime, there are fewer substrates to bind with enzymes; the reaction gets slower, until it eventually stops.
What are the factors affecting the rate of enzyme-controlled reactions?
- Enzyme concentration
- Substrate concentration
- Temperature
- pH
- Concentration of competitive reversible inhibitors
- Concentration of non-competitive reversible inhibitors
How does temperature affect the rate of enzyme reaction?
As the temperature increases, the kinetic energy and the enzyme activity increases as there’s more collisions until optimal temperature is reached (usually 40C). At optimal temperature, maximum rate of reaction is achieved. If the temperature continues to increase beyond optimal temperature, the rate of the reaction begins to decrease as more kinetic energy breaks the hydrogen bonds in the secondary and tertiary structure of enzyme. This changes the shape of the enzyme and its active site and causes the substrate to no longer fit. The enzyme is denatured.
How dose pH affect the rate of an enzyme reaction?
Any change in the pH value of the medium around the enzyme will cause ionic and hydrogen bonds to be damaged, this will change the 3-D shape of the enzyme and deform the active site. The substrate will therefore not be able to fit into active site so the reaction slows down or stops. The effects of pH is reversible within certain limits but if the pH is far from optimal value, the enzyme gets denatured.
How dose the enzyme concentration ffect the rate of an enzyme reaction?
As the concentration of enzymes is increased, there are more available active sites for substrates to fit into. More enzyme-substrate complexes are formed, more products are formed and the rate of reaction is increased. The limiting factor is the enzyme concentration. Once all substrates have formed enzyme-substrate complexes, a further increase in concentration will have no effect on the rate of reaction. At this point, the limiting factor is the substrate concentration. During comparison, look at initial rate to ensure differences in reaction rate are caused only by differences in enzyme concentration.
How does the substrate concentration affect the rate of the enzyme reaction?
As the concentration of the substrates increases, there are greater chances of collision with enzyme. More enzyme-substrate complexes are formed, more products are formed and the rate of reaction is increased. The limiting factor is the substrate concentration. Once all enzymes are occupied and working at maximum rate (vmax), a further increase in substrate concentration will have no effect on the rate of reaction. At this point, the limiting factor is the enzyme concentration.
What is an inhibitor?
Inhibitors are substances which stop the enzyme from binding to its substrate. Inhibitors interfere with enzyme activity and reduce the rate of an enzyme catalysed reaction. Therefore, as the concentration of inhibitors increases, the rate of reaction decreases.
Define reversible competitive inhibitor
Reversible competitive inhibitor have a similar shape to the substrate and fits into the active site. This reduces the number of enzyme-substrate complexes formed and the rate of reaction decreases. It is said to be reversible because it can be reversed by increasing the concentration of the substrate.
Define reversible non-competitive inhibitor
The reversible non-competitive inhibitor have a different shape to the substrate and fits into a site other than the active site. While the non-competitive inhibitor is bound, the tertiary structure of the entire enzyme is distorted, preventing the formation of enzyme-substrate complexes and decreasing the rate of reaction regardless of substrate concentration
What is end-product inhibition?
End-product inhibition is used to control metabolic reactions via non-competitive reversible inhibitors. As the enzyme converts substrate to product, it is slowed down because the end product binds to another part of the enzyme and prevents more substrate binding. However, the end-product can lose its attachment to the enzyme and go on to be used elsewhere, allowing the enzyme to reform into its active state.
What is feedback inhibition?
Feedback inhibition occurs when the end product binds to the enzyme at the start of the reaction/pathway and this stops the pathway until the concentration of the end product decreases
What is the theoretical maximum rate velocity?
Theoretical maximum rate velocity (Vmax) is the reaction rate is measured at different substrate concentrations while keeping the enzyme concentration constant. As substrate concentration is increased, reaction rate rises until the reaction reaches its maximum rate.
What is Michaelis-Menten equation?
Michaelis-Menten equation can be used to
calculate the maximum rate of reaction (Vmax) by
relating the velocity of enzyme reactions (V) to
concentration of a substrate [S]. Vmax represents
the maximum rate of reaction achieved by the
system at maximum substrate concentration.
How can you immobilise enzymes in alginate?
- The enzyme is mixed with a solution of sodium alginate.
- Little droplets of this mixture are then added to a solution of calcium chloride.
- The sodium alginate and calcium chloride instantly react to form jelly, which turns each droplet into a little bead. The jelly bead contains the enzyme.
- Can reuse the enzyme as it is not mixed with the solution, and can keep the product enzyme free, thus preventing contamination.
- More tolerant to PH changes as the enzyme molecules are held firmly in shape by the alginate beads, thus don’t denature easily.
- More tolerant to temperature changes as parts of the molecules embedded in the beads are not fully exposed to temperature or pH changes.
- Active site may be distorted by immobilizing
- Substrate passes through matrix when immobilized
- Some product is retained within matrix
What is a phospholipid membrane function and structure?
All cells and organelles are surrounded by a partially permeable membrane composed of a sea of phospholipids with protein molecules between the phospholipid molecules. The main function of the membrane is controlling the movement of substances in and out of the cell/organelle. However, it also contains receptors for other molecules to allow
signalling between cells.
What is the fluid mosaic model?
Fluid mosaic model is a model of the individual phospholipid and protein molecules and how they move around within their own monolayer. The word ‘mosaic’ describes the pattern produced by scattered protein molecule when the surface of the membrane is viewed from above. The fluidity of the phospholipid
membrane and the mosaic arrangement of the protein give the structure of the membrane its name – fluid mosaic mode.
What is the phospholipid bilayer?
Phospholipid bilayer provides the basic structure of membranes; it is selectively permeable and acts as a barrier to most water-soluble substances.
