Carbohydrates, Lipids, Proteins and Enzymes Flashcards
Which elements do carbohydrates contain?
Carbon, oxygen and hydrogen
What are monosaccarides?
A single sugar monomer that are soluble
What is a disaccharide?
Two monosaccharides covalently linked together by condensation reaction that are soluble
What is a polysaccharide?
Many monosaccharides covalently linked that is insoluble in water
What is a glyosidic bond?
Covalent bond between two sugar molecules
What does a condensation reaction do?
A hydrolysis reaction?
Condensation- link monosaccharides together
Hydrolysis- Breaks di- and polysaccharides down. Catalysed by specific enzymes
Give examples of monosaccharides
Glucose, fructose, galactose, ribose and deoxyribose
What are hexoses and what are pentoses?
Hexoses- six C atoms - glucose
Pentoses- five C atoms - ribose
Draw a- D- glucose
Draw beta- d- ribose
What are the similarities between glucose and ribose?
- All atoms in the ring are C except for one O
- There is one side chain
- All the C atoms except for the one with the attached side chain have one OH and H group
Which form do living organisms use?
D-forms (right handed)
Where is ribose found?
found in RNA and ATP
Draw b- D- glucose
Give examples of disaccharides
Lactose, maltose and sucrose
Give examples of equations of formation of disaccharides
glucose+glucose= maltose+ h2o
]glucose+ galactose = lactose+ H20
glucose+ fructose= sucrose+ H20
What are examples of polysaccharides?
Starch, cellulose and glycogen
What are the bonds that link glucose subunits?
Glycosidic bonds between C1 of one glucose and the C6 of another glucose
What happens in more branched molecules of glucose?
Glucose molecules can be loaded and unloaded more rapidly because there are more sites for glucose to attached or detached.
Describe cellulose (general)
Component of plant cell wall
Polymer of b-D-glucose
unbranched
Describe the orientation of glucose units in cellulose
Glucose units alternate so polymer is straight.
Cellulose molecules are aligned in parallel and are linked by hydrogen bonds forming bundles called cellulose microfibrils.
What are cellulose microfibrils?
They have high tensile strength and are the basis of plant cell walls and prevent cell bursting.
What is starch?
Store of glucose in plants bc it is insoluble in water. It allows large amounts of glucose to be stored without causing osmotic problems. It is energy store in seeds and storage organs
Describe the structure of starch
Polymer of a-D-glucose
Same orientation of glucose units so polymer is helical
Does not have a fixed size
Exists in two forms- amylose and amylopectin
Describe amylose and amylopectin
Amylose- 1,4 glycosidic bonds, is unbranched and has a helical shape
Amylopectin has some 1,6 glycosidic bonds in addition to 1,4 bonds, is branched and has a more globular shape.
What is glycogen?
Store of glucose in animals. Stored in liver and muscles. It is insoluble in water, large amounts can be stored without causing osmotic problems.
Describe glycogen in relation to its structure
Polymer of a-D- glucose
same orientation of glucose units so polymer is helical
has 1,4 and 1,6 glycosidic bonds so it is branched. It has more 1,6 glycosidic bonds than amylopectin so it is more branched and compact
Does not have a fixed size
What elements do lipids contain?
Carbon
Hydrogen
Oxygen
Describe the characteristics in lipids
Mostly/entirely hydrophobic
Insoluble in water
Diverse group
What are the three main types of lipids?
Triglycerides
Phospholipids
Steroids
What is the structure of a fatty acid and what is the general formula?
CH3(CH2)nCOOH
What is the range of the length of the fatty acid chain?
14-20 carbon atoms
What is the difference in saturated or unsaturated fatty acids?
Saturated fatty acids- all C atoms in the chain are linked to each other by single covalent bonds
Unsaturated fatty acids- there are one or more double bonds between C atoms. They are monosaturated if they have one double bond. They are polysaturated if they have more than one double bond
What can unsaturated fatty acids be?
Cis or trans
What is the structure of cis unsaturated fatty acids?
The H atoms are bonded to C atoms on the same side of a double bond. The molecule bends where there is a double bond. Thus they are loosely packed. The melting point is lower as they are less good at packing together so they are liquid at RT- oils.
What is the benefit of cis unsaturated fatty acids in the membrane?
Phospholipids with this increase membrane fluidity because the kinks make the fatty acids less good at packing and lower the mp.
What is the structure of trans unsaturated fatty acids?
The H atoms are bonded to C atoms on opposite sides of a double bond. Trans fatty acids do not have a bend but are straight molecules. Thus they are tightly packed and have a higher melting point and exist as a solid. They are produced artificially.
Describe triglycerides
Consist of three fatty acids and one glycerol
Each fatty acid is linked to glycerol through ester bond by a condensation reaction
Can be fats or oils
Used as energy stores, heat insulators and shock absorbers
Draw a triglyceride
Describe a phospholipid
Consist of one glycerol, two fatty acids and one phosphate group
Amphipathic
Structural component of membranes
Describe steroids
Structure with four fused rings
Ex- cholesterol, testosterone, oestrogen, progesterone
Function as hormones and cholesterol is a structural component of animal membrane
State the negative correlations found for CHD.
Populations that have diets rich in cis-monosaturated fatty acids have a negative correlation of CHD.
Possible explanations- large amounts of such fats, genetic, other aspects of their diet
State the positive correlation found in CHD
Positive correlation between large amounts of trans-fat consumed and rate of CHD. There is evidence that there is a causal link between consumption of trans-fats and CHD.
Compare and contrast carbohydrates and lipids as energy stores in humans
- Lipids and carbohydrates are both used for energy storage in humans.
- Lipids are stored as
fat/triglycerides and carbohydrates as glycogen - Lipids are long-term energy stores, while carbohydrates are short-term energy stores
- The amount of energy released in cell respiration per gram of lipid is double the amount released per gram of carbohydrates.
- Carbohydrates are mobilized/taken out of storage more rapidly than lipids making their energy more quickly available
- Carbohydrates are easier to transport than lipids making their energy more accessible. This is because small carbohydrates, e.g. glucose, are soluble in water and can be transported
in the plasma, whereas lipids/fatty acids are insoluble - Lipids can be used only in aerobic cell respiration, while glucose can be used in both aerobic and anaerobic respiration
- Glycogen is stored in liver and muscle, whereas lipids are stored in adipose tissue, which is
located beneath the skin and around some organs, e.g. the kidneys. Adipose tissue under the skin also functions as a heat insulator
What is Body Mass Index?
Used to assess whether a person’s body mass is at a healthy level
What is the formula for BMI?
Mass in kilograms/ (height in meters)2
Units are kg m-2
What does exergonic mean?
If the reactants have more energy than the products
What does endergonic mean?
If the reactants have less energy than the products
What are catalysts?
Substances that speed up chemical reactions without being changed themselves
What are enzymes?
Globular proteins that act as biological catalysts: they speed up reactions in cells by reducing the activation energy without being changed themselves
Where does the substrate bind?
Active site
What must a substrate have in order to take part in a reaction?
It has to gain energy to reach the transition state in which it is more likely to react- this is the activation energy.
What does the activation energy do?
Used to weaken the bonds within a substrate. Enzymes increase the rate of reaction by reducing the activation energy but the net change of the reaction is NOT changed
Describe the lock and key model
Enzymes are specific for their substrate- enzyme- substrate specificity
Enzyme- substrate specificity is due to the active site being specific for a substrate. The enzyme’s active site and the substrate have complementary shapes that fit together. They also have chemical properties that match each other .
The substrate and enzyme only bind to each other if there is a successful collision.
Substrates are converted into products while they are bound to the active site, the products are then released and the active site is free to catalyse another reaction.
Describe the induced fit model
As the substrate approaches, there is a conformational change of the enzyme and its active site so that the shape of the active site becomes complementary to that of the substrate improves its fit for the substrate
Binding to the active site results in weakening of the bonds within the substrate
The reaction occurs and substrate is converted into product. Products dissociate and the enzyme returns to its original conformation.
This is why enzymes exhibit broad specificity
What are factors that affect enzyme activity?
Temperature
pH
Substrate concentration/ enzyme concentration
Presence of inhibitor
What is the effect of temperature on enzyme activity?
As temperature increases, up to the optimum temperature enzyme activity increases. This is because as temp increases, the molecules gain more KE and move faster, so more collisions take place per unit time and there is a higher chance of successful collision. Above the optimum temperature, as temperature increases, enzyme activity decreases. This is bc the enzyme becomes denatured and its conformation including its active site are permanently changed. High temps cause vibrations within the enzyme which break the bonds.
What is the effect of pH on enzyme activity?
Each enzyme has an optimum pH at which its activity is maximum. As pH increases and decreases from the optimum, enzyme activity decreases. This is because the bonds between R groups which maintain the enzyme’s conformation are affected. As the pH deviated from the optimum, the enzyme’s conformation, including that of the active site is altered more and more. Above or below a certain pH the enzyme denatures and enzyme activity stops.
What is the effect of substrate concentration on enzyme activity?
At low substrate conc, as substrate conc increases enzyme activity increases steeply. This is bc as the substrate conc increases, there are more molecules of the substrate, so more collisions between substrate and active site. At higher substrate conc, enzyme activity increases at a slower rate bc many active sites are already bound w substrate. At high substrate conc, enzyme activity reaches a plateau and an increase in substrate conc has little effect on enzyme activity. This is because all enzyme molecules are saturated.
What are enzyme inhibitors?
Chemical substances that reduce or completely prevent enzyme activity
What are the 2 main types of enzyme inhibitors?
Competitive inhibitors
Non- competitive inhibitors
Describe competitive inhibitors.
The substrate and the inhibitor are chemically and structurally similar
Binding of inhibitor is reversible
Describe what happens with the competitive inhibitors.
- The inhibitor binds to the active site
- When the inhibitor occupies the active site, it prevents the substrate from binding and so enzyme activity slows down until the inhibitor dissociates.
- So inhibitor and substrate compete for the active site. As substrate conc rises, a substrate rather than an inhibitor molecule is increasingly likely to bind to a vacant active site
Give an examples of a competitive inhibitor
Malonate is a competitive inhibitor of succinate dehydrogenase
Describe the physical attributes of non- competitive inhibitors
The substrate and inhibitor are not similar
Give an example of a non-competitive inhibitor
Nitric Oxide synthase catalyses the production of nitric oxide from the amino acid arginine. Morphine is a non- competitive inhibitor of nitric oxide synthase
What happens with non-competitive inhibitors?
- The inhibitor binds to the enzyme at a different site than the active site called the allosteric site
- The inhibitor changes the conformation of the enzyme and this of the active site, so the active site cannot bind the substrate as well
- The rate of activity of the enzyme is lower at all substrate concentrations if a fixed low concentration of a non-competitive inhibitor is added and does not reach the maximum rate
- This is bc substrate and inhibitor are not competing for the same site. The substrate prevent the binding of the inhibitors, even at very high substrate conc
Draw a graph showing normal enzyme, competitive inhibitor and non-competitive inhibitor
Define metabolism
The web of all enzyme- catalysed reactions in a cell or organism
What is a metabolic pathway?
The chemical changes that happen in a sequence of steps and so the product of each step becomes the reactant for the next. Each reaction in teh pathway is catalysed by an enzyme
What does anabolic mean?
Reactions that synthesis larger molecules from simpler molecules
What does catabolic mean?
They break down larger molecules from smaller ones
Give an example of a chain reaction and of a cycle reaction
- Chain reaction- glycolysis
2. Cycle reaction- Krebs Cycle
What is end-production inhibitor?
The product of the last reaction inhibits the enzyme the catalyses the first reaction
Describe the control of metabolic pathways by end- product inhibitor
- The enzyme that is inhibited by the end- product is an allosteric enzyme
- When the end- product binds to the allosteric site of the enzyme, the enzyme’s conformation is altered so the shape of the active site is also altered so the substrate is less likely to bind to the active site.
- The binding of the inhibitor is reversible
Where is the control of metabolic pathways by end- product inhibitor used?
When there is an excess of the end product- negative feedback. The whole pathway is switched off and intermediates do not build up.
Give examples of end- product inhibitors
- The rate of cell respiration is controlled by allosteric inhibition of the first enzyme in the pathway, phosphofructokinase by ATP
- A pathway converts threonine to isoleucine. Threonine deaminase is the enzyme that catalyses the first reaction in the pathway and is inhibited by isoleucine.
What are enzyme inhibitors often used as?
Drugs
Describe how enzyme inhibitors are used for anti- malarial drugs
Malaria is a disease caused by the parasite Plasmodium. Plasmodium has evolved resistance to most anti-malarial drugs so there is a need for new drugs
- Scientists have sequenced the genome of Plasmodium and used it to determine its proteome
- From the proteome, enzymes involved in the parasitic metabolism have been identified as potential targets for inhibition.
- Using huge bioinformatics databases made it easier to search for inhibitors
- In one study, over 300,000 chemicals were screened to identify new chemicals that might act as inhibitors and were tested with Plasmodium enzymes.
What do immobilized enzymes do?
Immobilized enzymes are attached to another material or into aggregations, so that enzyme movement is restricted
What are methods of enzyme immobilization?
- Attachment to glass surface (adsorption)
- Entrapment in alginate gel
- Aggregation by bonding enzymes together into particles
What are advantages of enzyme immobilization?
- Better control of catalysis by adding or removing the enzymes at the ideal time
- Products are not contaminated with enzymes
- Enzyme can be retrieved and recycled thus reducing the cost
- Enzyme stability to temp and pH changes may be increased this reducing the rate of enzyme denaturation
- Substrates can be exposed to higher enzyme concentrations
Which inductries use enzymes?
Biotechnology Medical Food and nutrition Environmental Agriculture
State the equation of how lactose is hydrolysed
Lactose–> glucose + galactose (lactase)
How is lactase obtained?
From a yeast, which grows naturally in milk and is used for the production of lactose- free milk
How is lactose- free milk produced?
- Free lactase is added to the milk
- lactase is immobilized on a surface of a porous material
The result is milk w lower conc of lactose and higher conc of glucose and galactose
What are the advantages of producing lactose- free milk?
- Many people are lactose- intolerant and can only consume lactose- reduced milk
- Glucose and galactose are sweeter than lactose so less sugar needs to be added
- Lactose tends to crystallize during the production of ice-cream, giving a gritty texture. Glucose and galactose are more soluble they give a smoother texture
- Bacteria ferment glucose and galactose faster than lactose so the production of cottage cheese is faster.
What are amino acids?
Monomers that constitute polypeptides- there are 20 different amino acids
What is a polypeptide?
unbranched chain of amino acids linked together by peptide bonds
What is dipeptide?
two amino acids linked
What are peptides?
chains of up to 40 amino acids
What are proteins?
consist of one polypeptide or more than one polypeptides linked together. Proteins carry out most functions in cell
Which elements do polypeptides contain?
Carbon , Hydrogen, Oxygen and Nitrogen. Some also contain Sulphur
Draw the structure of amino acid
How are amino acids linked together?
By condensation reactions to form polypeptides. One water molecule is eliminated
What is the peptide bond?
It is formed between the amine group of one amino acid and the carboxyl group of another.
Draw the diagram showing the formation of a dipeptide
How many different amino acids are there?
20- it is the R group that differs
What are R groups?
They are chemically diverse eg. non- polar, positively or negatively charged.
What do amino acids determine?
The conformation and the properties of the protein
Why do some proteins not contain amino acids that are not in the basic repertoire of 20?
Bc of amino acid modification after polypeptide synthesis. In some species, an extra non- standard amino acid exists that is used by ribosomes. Here, the stop codon codes for the extra amino acid
For a polypeptide with n amino acids, how many possible sequences can there be?
20^n
What codes the amino acid sequence?
It is coded by genes. The base sequence of a gene determines the sequence of amino acids in the polypeptide. The gene is transcribed to mRNA and the mRNA is translated in ribosomes leading to the synthesis of a polypeptide. A codon codes for one amino acid based on the genetic code
What is a lysozyme and how many polypeptides does it contain?
1
Enzyme in secretions
What is integrin and how many polypeptides does it contain?
2
Membrane protein that facilitates adhesion between the cell and the extracellular matrix
What is collagen and how many polypeptides does it contain?
3
Structural protein in tendons, ligaments, skin and blood vessel walls that provides high tensile strength.
What is haemoglobin and how many polypeptides does it contain?
Four
Transports oxygen in red blood cells. It binds oxygen in the lungs and releases it in tissues
What determines the 3d conformation of a protein?
The conformation is determined by the amino acid sequence bc the 20 amino acids have diverse chemical properties and the way they interact determines how the protein folds
What happens in globular proteins?
The polypeptides gradually fold up as they are being synthesised. This is stabilised by intramolecular bonds between R groups of the amino acids that have been brought together by folding.
What happens in fibrous proteins?
The amino acid sequence prevents folding up and ensures the elongated shape of teh protein
Distinguish between globular and fibrous proteins
- Fibrous are long and narrow whereas globular are rounded/spherical
- The amino acid in fibrous proteins is repetitive where it is irregular in globular proteins
- Fibrous proteins are mostly insoluble in water whereas globular proteins are mostly soluble in water
- Fibrous proteins are less sensitive to changes in pH temperature whereas globular proteins are
- The common role of fibrous proteins is structural whereas for globular it is functional/metabolic
What are examples of fibrous proteins?
Collagen
Fibrin
Myosin
Spider silk protein
What are examples of globular protein?
Amylase
Haemoglobin
Insulin
Immunoglobulin
What is denaturation of a protein?
The permanent change in its conformation leading to loss of its function
Why does denaturation of proteins happen?
Because intramolecular bonds and interactions between R groups are disrupted or broken
What causes protein denaturation and how?
- Heat bc it causes vibrations within the molecule which breaks bonds
- Extremes of pH bc charges in R groups are changed and ionic bonds within the protein are affected
What are functions of proteins?
- Catalysis of chemical reactions by enzymes
- Structural proteins
- Hormones
- Receptors
- Membrane transport
- Immunity
- Packing of DNA
- Transport of nutrients and gases
- Movement/ muscle contraction
- Cell-cell adhesion
- Blood clotting
What does Rubisco do?
It is an enzyme that is responsible for carbon fixation during the Calvin cycle.
What is insulin?
A hormone secreted by beta cells of the pancreas and transported by the blood. It binds reversibly to hormone receptors in many cells causing the cells to absorb glucose.
What are immunoglobulins?
Antibodies that are produced by B lymphocytes. Each antibody recognises and binds a specific antigen aiding the destruction of the pathogen and activating an immune response
What is rhodopsin?
A pigment in rod cells of the eye. It absorbs light and is required for vision
What is collagen?
A structural protein and is used in skin adn walls of blood vessels to prevent tearing
What is spider silk?
A structural protein protein produced by spiders. It is use to produce lifelines on which spiders suspend themselves
What is a proteome?
All of the proteins produced by a cell or organism
What do cells in multicellular organisms have?
The same genome but different proteomes bc different cell types express different genes so produce different proteins
How do we visualise proteins?
Proteins are extracted form a sample and separated by gel electrophoresis. The proteins are stained and seen as bands. The thickness of the band indicated the amount of protein present.
What is the primary structure?
The sequence and number of amino acids in the polypeptide. The amino acids are linked by peptide bonds. The sequence of aa in the polypeptide is determined by the base sequence of the gene that encodes the protein. It controls all subsequent levels of protein organisation bc it determines the interactions between the R groups of amino acids
What is the secondary structure?
The formation of alpha helices and beta- pleated sheets stabilised by hydrogen bonding
Where do the hydrogen bonds form in the secondary structure?
Between the N-H group of one amino acid and the C-O group of an amino acid in another part of the chain
How are alpha helices and beta- pleated sheets represented?
alpha helices by helical ribbons and beta-pleated sheets by arrows
How do alpha-helix form?
When the polypeptide is wound into a right handed helix and hydrogen bonds form between adjacent turns of the helic
How do beta-pleated sheets form?
When sections of a polypeptide run parallel and hydrogen bonds form between them
What do sequences that do not form
neither an alpha helix nor
beta-pleated sheet exist as?
Random coils
What does the secondary structure
provide the polypeptide
chain with?
Mechanical stability
What is the tertiary structure?
The further folding of the polypeptide stabilised by interactions between the R groups. It is the overall 3d shape of the protein
What are the intramolecular interactions that occur in tertiary structure?
- Ionic bonds: between positively and negatively charged R groups
- Hydrophobic interactions: Non-polar amino acids orientate themselves toward the centre of the polypeptide to avoid contact with the water while polar aa orientate themselves outwards
- Disulphide bridges: Strong covalent bon formed between the R groups of 2 cysteines
Hydrogen bonds: between polar R groups
What is the quaternary structure?
the linking of polypeptides together to form a protein and the addition of non-polypeptide components/prosthetic groups
How is the quaternary structure stabilized?
ionic bonds, hydrogen bonds, disulphide bridges and hydrophobic interactions
What are conjugated proteins?
Proteins with a prosthetic group
