AS biology chapter one
- Created by: sbrown67
- Created on: 02-10-16 09:57
What is a covalent bond?
A bond formed between a shared pair of electrons on the outer shells of two atoms
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What is an ionic bond?
A bond formed between the electrostatic forces of attraction between oppositely charged ions
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What is a polar molecule?
A molecule that has an uneven distribution of electrons, causing an electronegative region in the molecule where more electrons tend to spend their time and a more positive region where there are fewer regions
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What is a hydrogen bond?
A bond formed between the electronegative region of one molecule and the slightly more positive region of another molecule. These bonds are relatively weak but collectively add strength to a molecule
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What is a monomer?
An individual sub-unit that join to form long chains of polymers
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What is a polymer?
A long chain of monomers that have joined
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What is a condensation reaction?
A reaction when two sub-units join that releases a molecule of water
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What is a hydrolysis reaction?
The addition of water in a reaction to break apart a polymer chain into its substituent monomers
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What is metabolism?
All the chemical reactions that take place in the human body
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What is a mole?
The SI unit for measuring the amount of a substance
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How many atoms does one mole of a substance contain?
One mole contains the same number of atoms as 12g of carbon-12
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What is Avogadro's constant?
The number of atoms in 12g of carbon-12 6.022 x 10^23
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What is a molar solution?
There is one litre of solution for every mole of solute
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What unusual feature does carbon have?
Carbon atoms readily form bonds with other carbon atoms, allowing a backbone of carbon atoms to form, on which, other atoms can be placed
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What are organic molecules?
Carbon-containing molecules
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What 4 elements are most organic molecules based on?
Carbon, hydrogen, oxygen, nitrogen
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What is a monosaccharide?
A sweet-tasting, soluble substance
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What is the general formula of monosaccharides?
(CH2O)n where n can be any number from 3 to 7
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What are some examples of monosaccharides?
Glucose, fructose, galactose
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What are the two isomers of glucose?
Alpha-glucose and beta-glucose
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Draw the displayed formula for alpha- glucose
()
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Draw the displayed formula for beta-glucose
()
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What is a reducing sugar?
A sugar that donates electrons to other chemicals
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Which sugars are reducing sugars?
All monosaccharides and some disaccharides (e.g. maltose)
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What is the test for reducing sugars?
Benedict's test
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What is Benedict's reagent?
An alkaline solution of copper (II) sulphate
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Outline the stages of Benedict's test
1. 2cm^3 of sample in a test tube 2. 2cm^3 of Benedict's reagent in the test tube 3.Place the test tube in a gently boiling water bath for 5 minutes
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If a reducing sugar is present, what will the result of Benedict's test be?
A red precipitate of copper (I) oxide will form
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What is the test for non-reducing sugars?
Do the Benedict's test and if there is a negative result: 1. Add 2cm^3 of sample to test tube 2. Add 2cm^3 of hydrochloric acid to the test tube and heat in gently boiling water bath for 5 minutes 3. Add sodium hydrogen carbonate 4. Add Benedict's
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Why is the hydrochloric acid used in the test for non-reducing sugars?
This hydrolyses the bonds between the monosaccharides
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Why is the sodium hydrogen carbonate added to the test for non-reducing sugars?
This neutralises the solution because Benedict's reagent does not work in acidic conditions
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What will the result be if a non-reducing sugar was present in the original sample?
An orange/brown precipitate will form
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What is a disaccharide?
When monosaccharides are combined in pairs
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Which two monosaccharides combine to form maltose?
Glucose and glucose
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Which two monosaccharides combine to form sucrose?
Glucose and fructose
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Which two monosaccharides combine to form lactose?
Glucose and galactose
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When two monosaccharides combine, what type of reaction do they undergo?
A condensation reaction
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What type of bond is formed between two monosaccharides?
A glycosidic bond
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What can be added to a disaccharide to break it down into its substituent monosaccharides?
A water molecule
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What is polysaccharide?
A long chain of combined monosaccharides
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When polysaccharides are hydrolysed, what do they form?
Monosaccharides and disaccharides
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What can polysaccharides be used for?
Storage, structural support
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What is starch?
A polysaccharide found in many parts of plants in the form of small starch grains
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How is starch formed?
The joining of between 200 and 100 000 a-glucose molecules by glycosidic bonds in a series of condensation reactions
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What is the test for starch?
The iodine test 1. Add 2cm^3 of sample to test tube 2. Add two drops of iodine solution and stir 3. Presence of starch is indicated by a colour change from orange to blue/black
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Are the chains branched or unbranched in starch chains?
They can be either branched or unbranched
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What is the main role of starch?
Storage
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How is the structure of starch suited for storage?
1.Large and insoluble- doesn't affect water potential so no osmotic gain in cells 2. Insoluble- doesn't diffuse out of cells 3.Compact-can be stored in small space 4. When hydrolysed, forms glucose- easily transported and used in respiration
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What is useful about branched chains of starch?
Has many ends, which can be acted on simultaneously by enzymes so glucose molecules can be released rapidly
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What is glycogen?
A storage molecule found in animal cells
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What is the structure of glycogen?
Similar to starch, but has shorter chains
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Where and how is glycogen stored?
As small granules, found mainly in muscles and the liver
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Why is the mass of carbohydrate stored in animals relatively small?
There is a much larger amount of fat stored in the body as it is the main storage molecule in animals
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How does the structure of glycogen aid its function of storage?
1. Large and insoluble- doesn't affect water potential 2. Insoluble- doesn't diffuse out of cells 3. Compact- stored in a small space
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Glycogen is more highly branched than starch, how does this help animals?
There are many ends that enzymes can simultaneously work on so glucose can be rapidly released. This is important for animals as they have a high metabolic activity as they are more active.
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What is cellulose?
A structural polysaccharide found in the cell wall of plants
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How does cellulose differ from starch and glycogen?
1. Glycogen is made of monomers of beta-glucose 2. Rather than forming a coiled chain, cellulose has straight, unbranched chains that run parallel to each other
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What forms between adjacent cellulose chains?
Hydrogen bonds form cross linkages between the adjacent chains
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How are the beta-glucose molecules arranged in a chain?
The adjacent beta glucose molecules are rotated by 180 degrees, allowing hydrogen bonds to form between hydroxyl groups on adjacent parallel chains that help to give its structural stability
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What is the role of cellulose in a plant cell?
1. Provides strength to plant cell 2. Prevents cell from bursting by osmotic pressure 3. Cells are turgid and stem and leaves are kept in a turgid state, which is important for maximising surface area for photosynthesis
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How does the structure of cellulose help its functions of giving rigidity and support?
1.Made of beta-glucose molecules- straight, unbranched chains 2. Molecular chains run parallel to each other- cross-linked by hydrogen bonds, adding strength 3. Molecules are grouped in microfibrils which are grouped in fibres, adding more strength
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What are the characteristics of lipids?
1. Contain carbon, hydrogen & oxygen 2. Proportion of oxygen to carbon and hydrogen is small than in carbohydrates 3. Insoluble in water 4. Soluble in other organic solvents, e.g ethanol, acetone
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What are the functions of lipids?
1. Cell membranes 2. Water proofing 3. Protection 4. Insulation 5.Energy storage
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Wha are the roles of lipids in cell membranes?
The contribute to the flexibility of membranes and the transfer of lipid-soluble substances across them
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What are the roles of lipids in water proofing?
They are insoluble in water 1. Plants have waxy lipid cuticles to reduce water loss 2. Some mammals have an oily secretion from the sebaceous glands
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What are the roles of lipids in protection?
They are often found around the delicate organs e.g. the kidney
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What are the roles of lipids in insulation?
Lipids are poor conductors of heat. When stored under the skin, they help reduce heat loss 2. They are used as electrical conductors also, they are stored around the myelin sheath on nerve cells
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What is the role of lipids in energy storage?
When oxidised, fats provide more than twice the energy as the same mass of carbohydrates
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What physical states are fats and oils at room temperature (10-20 degrees)?
Fats are solids, oils are liquids
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What is the structure of a triglyceride?
Three fatty acids are bonded to a glycerol molecule
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What type of bond is present between the fatty acids and the glycerol molecule in a trigylceride?
An ester bond between the hydroxyl group in the carboxyl group on the fatty acid, and the hydrogen from the hydroxyl group on the glycerol molecule
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What type of reaction occurs when the fatty acids combine with the glycerol?
Condensation
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Where does the variation in triglycerides come from?
The glycerol molecules are the same so variation arises from the difference in the hydrocarbon chain on the fatty acids
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What group do all fatty acids contain?
-COOH with a hydrocarbon chain attached
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What is the structural formula of a glycerol molecule?
CH2OH(CHOH)(CH2OH)
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What is the difference between a simple triglyceride and a mixed triglyceride?
1.Simple triglyceride consists of the same three fatty acids 2. Mixed triglycerides consist of different fatty acids
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What is an unsaturated fat?
The hydrocarbon chain on the fatty acids contains a double carbon=carbon bond, causing a kink in the chain
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What is a saturated fat?
The hydrocarbon chain on the fatty acid consists of single bonds only, each carbon atom is bonded to the maximum number of hydrogen atoms (it is saturated with hydrogen)
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What is the difference between mono-unsaturated fats and poly-unsaturated fats?
Mono-unsaturated fats consist of only one double bond, polyunsaturated fats consist of more than one double bond
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Why are unsaturated fats liquid at room temperature, and saturated fats are solid?
Unsaturated fats contain a double carbon=carbon bond, which causes a kink in the hydrocarbon chain. This means the chains cannot pack closely together
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How is the structure of a triglyceride related to its properties?
1. High ratio of energy storing carbon-hydrogen bonds 2. Low mass to energy ratio- much energy can be stored in a small volume 3. Large, non-polar molecules- doesn't affect water potential 4. High ratio of hydrogen to oxygen atoms
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Why is having a high ratio of hydrogen to oxygen atoms beneficial?
When oxidised, triglycerides release valuable water molecules, which is very helpful to organisms living n the desert
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What is a phospholipid?
Like a triglyceride, but one of the fatty acids is replaced by a phosphate group
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Why are phospholipids said to be polar?
The phosphate group (the head) is hydrophilic and the fatty acids (the tail) are hydrophobic
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Which two parts are a phospholipid made up of?
A hydrophilic head, which interacts with water, but not with fat and a hydrophobic tail which repels water but interacts with fat
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What happens when a phospholipid is placed in an aqueous environment?
They position themselves so the tail is as far away from the water as possible and the head is as close to the water as possible.
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What do phospholipids form when in an aqueous environment?
A phospholipid bilayer- a hydrophobic barrier is formed between the inside and the outside of the cell
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How is the structure of a phospholipid related to its properties?
1. Polar molecule- forms a phospholipid bilayer 2. Hydrophilic phosphate head help to hold the molecule at the surface of the cell-surface membrane 3. Allows formation of glycolipids by combining with carbohydrates- important in cell recognition
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What is the test for lipids?
The emulsion test 1. Add 2cm^3 of sample with 5cm^3 of ethanol to test tube 2. Shake thoroughly to dissolve lipids 4. Add 5cm^3 water, shake gently 5. Cloudy white colour indicates lipid
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What control test could be done to compare the results of the emulsion test to?
The same procedure using water instead of the sample, the result solution will be clear
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Why does the resultant solution in the emulsion tests appear cloudy-white?
There are droplets of lipid finely dispersed throughout the water to form an emulsion. Light, as it passes through, will be refracted as it passes from oil droplets to water droplets
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What are proteins?
-Usually very large molecules where the shape of each protein differs from that of all other proteins
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What can polypeptides combine to form?
Proteins
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What basic monomer are polypeptides made from?
A combination of amino acids
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How many naturally occurring amino acids have been discovered in proteins?
20
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What is the structure of an amino acid?
A central carbon atom attached to 4 other different chemical groups
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What are the four different chemical groups present in an amino acid?
1. A carboxyl group (-COOH) 2. An amino group (-NH2 3. A hydrogen atom (-H) 4. An R group (a side group of different chemical groups- each amino acid has a different R group)
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What is a dipeptide?
A combination of two amino acids formed by a condensation reaction
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Where does the water molecule come from during a condensation reaction between two amino acids?
The -OH from the carboxyl group and the -H from the amino group of a different amino acid
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What sort of bond is present between two amino acids?
A peptide bond
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Where is a peptide bond formed?
A peptide bond is formed between the carbon atom of one amino acid and the nitrogen atom of another amino acid
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What reaction can peptide bonds be broken by?
Hydrolysis
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What is the primary structure of a polypeptide?
A series of condensation reactions combines a specific sequence of amino acids (determined by the DNA)
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What is the definition of primary structure of protein?
The sequence of amino acids found in its polypeptide chains
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What does the primary structure of a protein determine?
The ultimate shape of the protein, and hence its function
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What is the difference between a simple protein more common protein?
A simple protein consists of just one polypeptide chain, while most proteins consist of many polypeptide chains
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What is the secondary structure of a protein?
The shape which the polypeptide chain forms as a result of hydrogen bonding
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Which part of the polypeptide chain form the hydrogen bonds ing in the secondary structure of proteins?
The hydrogen of the -NH group has an overall positive charge and the O of the -C=O group has an overall negative charge. These two groups readily form weak hydrogen bonds
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What do the hydrogen bonds in the secondary structure of proteins cause?
They cause the polypeptide chain to twist into a 3-D shape, such as the alpha-coil or a beta-pleated sheet
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What is the tertiary structure of proteins?
The bending and twisting of the polypeptide helix into a compact structure. Three types of bonds contribute to the maintenance of the tertiary structure
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What types of bonds are present in the tertiary structure of proteins?
1.Disulfide bridges-fairly strong, so not broken easily 2. Ionic bonds between any carboxyl and amino groups that are not involved in forming peptide bonds- weaker than disuflide bonds and broken easily by changes in pH 3. Hydrogen bonds- break easil
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Why is the tertiary structure of proteins so important?
It is the 3-D shape of a protein that is important to how it functions. It makes each protein distinctive and allow it to interest with other molecules in a very specific way
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What is the quaternary structure of a protein?
Arises from the combination of a number of different polypeptide chains and associated non-protein groups into a large, complex molecule e.g. haemoglobin
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Are there only polypeptide chains present in the quaternary structure of proteins?
NO- there are other non-protein (prosthetic) groups involved e.g. the iron-containing haem group in haemoglobin
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What is the test for proteins?
Biuret test- detects peptide bonds
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How would you carry out the Biuret test?
1. Place solution of sample in test tube with equal volume of sodium hydroxide at room temp 2. Add few drops of 0.05% copper (II) sulphate solution and mix gently
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What colouration in the Biuret test indicates a peptide bond, and hence a protein?
Purple- if no protein is present, the solution remains blue
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What are the two main types of protein?
Fibrous and structural
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What is a fibrous protein?
Any protein with a structural function e.g. collagen
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What is a globular protein?
Any protein with a metabolic function e.g. enzymes and haemoglobin
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Why are fibrous proteins such good structural materials?
They form long chains which run parallel to each other and are linked by cross-bridges so they from very stable molecules
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What is the structure of collagen?
Primary: unbranched polypeptide chain Secondary: polypeptide chain is very tightly wound- enzyme glycine helps tight packing Tertiary: twisted into second helix Quaternary: 3 chains wound together like a rope
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What are the individual polypeptide chains in collagen held together by?
Bonds between amino acids of adjacent chains
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How are the endings and beginnings of chains distributed in collagen?
The point where one chain ends and the next one begins are spread throughout the fibre, rather than just being in the same position along it
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How do bonds between amino acids of adjacent groups increase the strength of collagen?
Prevents the individual chains from sliding past one another so they gain strength as they act as a single unit
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Why does the quaternary structure of collagen make it a suitable molecule for a tendon?
The three polypeptide chains wound together form a strong, rope-like structure that has strength in the direction of pull of a tendon
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Why is the arrangement of the beginnings and endings of the fibres in collagen helpful for the structural role of collagen?
The junctions between adjacent collagen molecules are points of weakness, so these points of weakness are spread throughout the fibre to prevent it from breaking, like it would if they all occurred at the same point
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What is an enzyme?
Globular proteins that act as biological catalysts. They are not altered by the chemical reaction and can be reused over and over again
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What conditions must be satisfied for a reaction to take place naturally?
1. Reactants must collide with sufficient energy to alter the arrangement of their atoms 2. The free energy of the reactants must be more than that of the products 3. The activation energy needs to be reached
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What is free energy?
The energy of a system that is available to perform work
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How do enzymes work?
They lower the activation energy, allowing reactions to take place at a lower temperature, these reactions are often needed to sustain life
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What is the structure of an enzyme?
It has avery particular 3-D structure determined by the sequence of amino acids
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What is the name of the molecule on which the enzyme acts?
Substrate
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What is the active site?
A specific region of the enzyme that is functional- it forms a depression within the larger enzyme and is made up of a small number of amino acids
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What is an enzyme-substrate complex?
When the substrate fits into the active site and is held there by hydrogen bonds between certain amino acids of the active site and groups on the substrate molecule
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How is the substrate held in the active site?
Via two ionic bonds caused by the transfer of an H+ ion from a -COOH group in the side chain of one amino acid to an -NH2 group on the side chain of another amino acid
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Other cards in this set
Card 2
Front
What is an ionic bond?
Back
A bond formed between the electrostatic forces of attraction between oppositely charged ions
Card 3
Front
What is a polar molecule?
Back
Card 4
Front
What is a hydrogen bond?
Back
Card 5
Front
What is a monomer?
Back
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