Biological Molecules Flashcards
covers key concepts in the first part of section one
What are monomers?
Monomers are small units which are the components of larger molecules.
What are polymers?
Polymers are molecules made from many monomers joined together.
What are examples of monomers?
Monosaccharides, amino acids and nucleotides
What are examples of polymers?
Polysaccharides, polypeptides and polynucleotides
What reaction allows two monomers to bond together?
A condensation reaction allows two monomers to be joined together by a chemical bond, releasing a water molecule.
What reaction breaks the chemical bond between two molecules?
A hydrolysis reaction allows the chemical bond to break between two molecules and this happens due to the addition of water.
What are carbohydrates?
Carbohydrates are molecules which consist only of carbon, hydrogen and oxygen.
What is the small unit that makes up a carbohydrate?
Monosaccharides
What is formed when two monosaccharides go through condensation reaction?
A disaccharide is formed.
What is the special bond that is formed during the condensation reaction between two monosaccharides?
A glycosidic bond
What is formed when many monosaccharides go through condensation reaction?
A polysaccharide is formed.
What are examples of monosaccharides?
- Glucose (α-glucose and β glucose)
- Galactose
- Fructose
What is the structure of both α-glucose and β glucose?
They both have 6 carbon atoms, α-glucose has its OH group attached at the bottom right and β glucose has its OH group attached at the top right.
Which disaccharide is formed when two α-glucose molecules join together?
Maltose
Which disaccharide is formed when a glucose molecule and fructose join together?
Sucrose
Which disaccharide is formed when a glucose molecule and galactose join together?
Lactose
What are the three polysaccharides that are formed from glucose monomers?
- Glycogen (formed by the condensation of α-glucose)
- Starch (formed by the condensation of α-glucose)
- Cellulose (formed by the condensation of β glucose)
What is starch?
Starch is what plants store as excess glucose. When plants require glucose for respiration and energy, starch is broken down into glucose.
What mixture does starch consist of?
Amylose and Amylopectin
Describe the structure of starch?
Amylose is a long, unbranched chain of α-glucose molecules. Due to its specific glycosidic bonding, its shape becomes coiled, which makes it very compact.
Amylopectin is a long, branched chain of α-glucose molecules. It has got many side branches on it.
Explain the relationship between the structure and function in starch.
The coiled and compact shape of amylose allows a lot of energy to be stored, therefore making it good for energy storage.
The side branches on amylopectin allow enzymes to break down the molecule and make it easier to break the glycosidic bond. This means that energy can be released quicker for important functions like respiration.
Starch is also insoluble and therefore do not affect the water potential, so water cannot enter cells by osmosis.
What is the test for starch?
Add the test sample to iodine solution (potassium iodide solution).
If the solution turns from brown/orange to blue/black, then starch is present.
What is glycogen?
Glycogen is the main energy storage in animals and it stores excess glucose to be used later on, such as respiration.
Describe the structure of glycogen.
Glycogen has a large number of side branches, similar to amylopectin’s structure.
Explain the relationship between the structure and function in glycogen.
The side branches in glycogen allow it to be broken down much quicker by enzymes, meaning that energy can be released quickly as well.
Also, since it is highly branched, a high amount of energy is released. The energy released can be used for important processes such as respiration.
Glycogen is also insoluble and therefore do not affect the water potential, so water cannot enter cells by osmosis.
What is cellulose?
Cellulose is the main component found in cell walls to help provide structural support.
Describe the structure of cellulose.
Cellulose is a long, straight, unbranched chains of β glucose molecules. Each chain is linked together by hydrogen bonds to form strong cross links and strong fibres known as microfibrils.
Explain the relationship between the structure and function of cellulose.
The microfibrils help provide structural support for the cell wall, meaning that it can help the cell wall to not burst when water tries to enter in.
The strength of the cell wall is contributed by the many hydrogen bonds that are between the cellulose chains, making cellulose a strengthening material for plants.
What is the test for reducing sugars?
- Add test sample to Benedict’s Reagent.
- Heat it gently.
- If solution turns brick red, then a reducing sugar is present.
- If the solution stays blue, then no reducing sugar is present.
What is the test for non-reducing sugars?
After the test for reducing sugars, you should:
- Add dilute hydrochloric acid to the test sample (hydrolyse the polysaccharides/disaccharides into its constituent monosaccharides).
- Then add sodium hydrogencarbonate to neutralise the acid. (Benedict’s reagent does not work in acidic conditions).
- Add the sample to Benedict’s reagent and then heat the sample.
-If the solution turns brick red then a non-reducing sugar is present. If the solution stays blue then there isn’t a non-reducing or reducing sugar present.
What are lipids?
Lipids are biological molecules that are composed of carbon, hydrogen and oxygen and they are only soluble in organic solvents (such as alcohols) and insoluble in water.
What are the two types of lipids called?
Triglycerides and Phospholipids
How are triglycerides formed?
Triglycerides are formed by the condensation reaction of one glycerol molecule and three fatty acid chains.
What is the bond formed between the glycerol molecule and each fatty acid chain?
Ester bond
What are the two types of fatty acids called?
Saturated fatty acids and Unsaturated fatty acids
What is the difference between saturated and unsaturated fatty acid chains?
Saturated fats do not have double bonds between their carbon atoms.
Unsaturated fats do have double bonds between carbon atoms.
What does the double bonds cause the fatty acid chain to do?
It causes the fatty acid chain to kink/bend, causing the chain to not be able to pack together tightly and therefore are liquids in room temperature (oils).
How does triglyceride’s structure relate to their properties?
- Triglycerides have a high ratio of energy storing carbon-hydrogen bonds to carbon atoms and therefore are an excellent source of energy.
- Triglycerides have a low mass to energy ratio, meaning that they are a good storage molecules.
- Triglycerides insolubility (due to being large and non-polar) in water means that their storage does not affect the water potential of cells.
How does the structure of a phospholipid molecule look like?
In phospholipids, one of the fatty acid chains is replaced by a phosphate group/phosphate head.
Fill in the gap: The phosphate group is _______________ to water and therefore is ______________________.
The phosphate group is attracted to water and therefore is hydrophilic.
Fill in the gap: The fatty acid chains _______________ water and therefore are ________________.
The fatty acid chains repel water and therefore are hydrophobic.
How does phospholipid’s structure relate to their properties?
- Since phospholipids have a hydrophilic and hydrophobic side, the molecule is polar meaning that when placed in water, they form a bilayer. The hydrophilic head holds at the surface of the cell membrane.
- This phospholipid bilayer is what forms the cell membranes, which controls what enters and leaves the cell.
- The centre of the bilayer is hydrophobic, meaning water soluble substances cannot enter easily.
What is the test for lipids?
The test for lipids is known as the emulsion test.
The steps are:
- Add test sample with ethanol in a test tube.
- Shake it thoroughly.
- Pour the solution in water.
- If there is a cloudy white/milky colour then this indicates that a lipid is present.
What are proteins?
Proteins are biological molecules that are composed of carbon, hydrogen, oxygen and nitrogen and they come in all shapes and sizes.
What are the monomers of proteins?
The monomers of protein are amino acids.
What do you form when two amino acids join together?
A condensation reaction takes place forming a dipeptide.
What do you form when more than two amino acids join together?
A condensation reaction takes place forming a polypeptide.
Describe the structure of an amino acid.
- Amine Group (H2N)
- Carboxyl Group (COOH)
- A variable carbon-containing group (R)
- A hydrogen (H)
How many different amino acids can you get?
There are 20 different amino acids, each determined by their different R groups.
What bond is formed during a condensation reaction of amino acids?
A peptide bond is formed between the amino acids.
What are the 4 structures that proteins are called and explain them?
They are called:
-Primary structure: The sequence of amino acids that makes up the polypeptides of a protein.
-Secondary structure: The way in which the chain of amino acids of the polypeptides of a protein is folded. Hydrogen bonds form between the amino acids, to form 3D shapes like an alpha helix or beta pleated sheet.
-Tertiary structure: the folding of a whole polypeptide chain in a precise way, as determined by the amino acids of which it is composed. Hydrogen bonds, ionic bonds and disulfide bridges are formed.
-Quaternary structure: More than one polypeptide chains linked together and held by bonds.
In the tertiary structure, why do ionic bonds and disulfide bridges form?
Ionic bonds form due to the attraction between negative and positive charges on different parts of the molecule. These can easily be broken by pH changes.
Disulfide bridges form when interaction between the amino acid cysteine occurs. These are usually strong and not easily broken.
What determines the function of a protein?
The shape of the protein.
Describe the test for proteins?
The test for proteins is known as the biuret test.
The steps are:
- Add the test sample to a test tube.
- Then add sodium hydroxide solution.
- Then add copper(II) sulfate solution.
- If the solution turns from blue to purple, then it indicates that protein is present.
What is an enzyme?
Enzymes are biological catalysts that increase the rate of reaction by lowering the activation energy of the reaction they catalyse.
Which protein structure do enzymes have?
Enzymes have a tertiary structure, which is why enzymes are highly specific.
What reactions do enzymes catalyse?
Metabolic reactions (intracellular and extracellular)
What is the active site on an enzyme?
The active site, which has a specific shape, is the part of an enzyme where the substrate molecules bind to.
What is formed when a substrate fits into an enzyme’s active site?
An enzyme-substrate complex
Explain the induced-fit model.
The induced fit model proposes that when an enzyme and a substrate interact with each other, a change is induced in the shape of the active site, moulding around the substrate molecule.
The change in shape of the active site puts pressure/strain/stress on certain bonds in the substrate, lowering the activation energy required to break the bond.
How are the properties of enzymes related to their tertiary structure?
Their tertiary structure allows enzymes to be highly specific, meaning that it will usually catalyse one reaction since their active site is complementary to a specific substrate.
Each different enzyme has a different tertiary structure and so a different active site.
What are the 6 factors that affect enzyme activity?
- Temperature
- pH
- Enzyme concentration
- Substrate concentration
- Concentration of competitive inhibitors
- Concentration of non-competitive inhibitors
How does temperature affect enzyme activity?
Temperature from start to optimum:
- Increases kinetic energy of molecules.
- Molecules move more rapidly.
- Increase in chances of successful collisions.
- Increases chance of forming enzyme-substrate complex.
- Increases rate of reaction.
Temperature higher than optimum:
- Bonds holding the tertiary structure break.
- Active site shape is lost.
- Substrate can no longer be complementary.
- Enzyme-substrate complex cannot be formed.
- Enzyme denatured and rate of reaction decreases.
How does pH affect enzyme activity?
- All enzymes have an optimum pH.
- When an enzyme has a pH above or below their optimum temperature, ions found in the acid or alkali cause the bonds that hold the tertiary structure to break.
- Therefore the active site shape is lost and enzyme-substrate complexes can no longer be formed.
- The enzyme is denatured.
How does the substrate concentration affect enzyme activity?
Increasing the substrate concentration means that:
- more chance of successful collisions.
- more chance of forming enzyme-substrate complex, therefore increasing rate of reaction.
- this continues until the maximum rate of reaction is reached (when all the active sites are full/occupied).
How does the enzyme concentration affect enzyme activity?
Increasing the enzyme concentration means that:
- more chance of successful collisions.
- more chance of forming enzyme-substrate complex, therefore increasing rate of reaction.
- this continues until the maximum rate of reaction is reached (when all the substrates are used).
What is a competitive inhibitor?
A substance with a similar shape to the substrate and a complementary shape to the enzyme’s active site.
What is a non-competitive inhibitor?
A substance, with a different shape that binds to an enzyme and reduces its activity.
How does the concentration of competitive inhibitors affect the enzyme activity?
A competitive inhibitor binds to the active site, blocking substrates from binding instead, preventing enzyme-substrate complex from forming, and the rate of reaction increases at a lower rate.
How does the concentration of non-competitive inhibitors affect the enzyme activity?
A non-competitive inhibitor binds to another site on the enzyme, causing the active site’s shape to change, meaning that the substrate is not complementary and less enzyme-substrate complexes are formed, resulting in a lower rate of reaction.
