2.2 Biological molecules Flashcards
What are hydrogen bonds?
Hydrogen bonds form between the positive and negatively charged regions of adjacent water molecules
What is water?
Water is the medium in which all metabolic reactions take place in cells
What are the properties of water?
- Liquid at room temperature
- Density
- Solvent
- Cohesion
- Surface tension
- High specific heat capacity
- High latent heat of vaporisation
- Reactant
Liquid at room temperature
- Provides habitats for living things in rivers, lakes, seas
- Form a major compound of the tissues in living organisms
- Provide a reaction medium for chemical reactions
- Provide an effective transport medium
Density
Ice is less dense than water
- Aquatic organisms have a stable environment in which to live through the water
- Layer of ice reduces the rate of heat loss from the rest of the pond - insulated against the extreme cold
Solvent
Water molecules attracted to the negative and positive parts of the solute
Water moleucles cluster around the charged parts of the solute molecules and help separate them and keep them apart
- Molecules and ions can be transported around living things whilst dissolved in water
Cohesion and surface tension
Cohesion - hydrogen bonding between molecules pull them together
Surface tension - Water molecules at surface are all hydrogen bonded to the molecules beneath them and hence more attracted to the water molecules beneath than the air molecules above
pond skaters walking on water
High specific heat capacity
Amoount of energy required to raise temp of 1kg by 1 degrees celsius
Water molecules are held quite tightly by hydrogen bonds so we need to put in a lot of heat energy to increase their kinetic energy
- Do not heat up or cool down slowly
- Living things need a stable temperature for enzyme controlled reactions to happen properly
High latent heat of vaporisation
Heat energy that helps molecules to break away from each other and become a gas
Relatively large amount of energy is needed - helps cool living things and keep temperature stable
- Mammals are cooled when sweat evaporates
Reactant
In reactions such as photosynthesis and hydrolysis reactions such as digestion of starch, proteins and lipids
What is a polar molecule?
When a molecule has one end that is negatively charged and one end that is positvely charged.
For example water
Why is the sharing of electrons uneven in water when it is electrically neutral as a whole?
The oxygen atom attracts the electrons more strongly than the hydrogen atoms. This results in a weak negatively charged region on the oxygen atom and a weak positively charged region on the hydrogen atoms
What is a dipole?
The seperation of charge due to the electrons in the covalent bonds being unevenly shared
What are the elements in each biological molecule?
Carbohydrates: C,H and O
Lipids: C,H and O
Proteins: C, H, O, N and P
Nucleic acids: C, H, O, N and P
What is alpha and beta glucose and ribose and deoxyribose?
Alpha:
- Energy source
- Component of starch and glycogen, which acts as energy stores
Beta:
- Energy source
- Component of cellulose which provides structural support in cell walls
Ribose:
- Component of RNA, ATP and NAD
Deoxyribose - component of DNA
What monosaccharides join up to make the 3 disaccharides?
Maltose - alpha glucose 2x
Sucrose - alpha glucose and fructose
Lactose - galactose and beta glucose
What are the three monosaccharides?
monomers
Glucose, Fructose and galactose
What are disaccharides?
They are made from two monosaccharides. They are joined together by a glycosidic bond and are formed via a condensation reaction
What are the three disaccharides?
dimers
Sucrose, maltose and lactose
What are the three polysaccharides?
polymers
Starch, cellulose and glycogen
What is the structure of starch?
Amylose:
- Alpha glucose, 1-4 glycosidic bonds
- Coils into spiral shape and hydrogen bonds hold it into shape
- Less soluble
Amylopectin:
- 1-6 glycosidic bonds and 1-4
- Has branches formed by glycosidic
- Coils into a spiral shape but with branches emerging from the spiral
What is the structure of cellulose?
Tough, insoluble and fibrous structure made up of beta glucose molecules (straight chained)
- Every other beta glucose molecule is rotated 180 degrees to prevent the chain form spiralling
- Hydrogen bonding between the molecules give it additional strength and it stops it spiralling
- Hydroxyl group on carbon 2 sticks out, enabling hydrogen bonds to be formed between chains - gives structure additonal strength
What are the functions of cellulose and how does the structure allow that?
Provides collective strength due to having many hydrogen bonds.
Won’t affect water potential because it is insoluble
What are the functions of starch and how does the structure allow that?
- Helix can compact to fit a lot of glucose in a small space.
- Branched stucture increases surface area for rapid hydrolysis.
- It is insoluble so it wont affect water potential
What is glycogen?
- In animals and fungi
- Branches between carbon 1 and 6
- More branched than amylopectin causing it to be more compact
- Easier to remove monomer units as there are more ends
Why are polysaccharides good energy stores?
Glycogen and starch are compact - do not occupy a large amount of space
Polysaccharides hold glucose molecules in chains so they can be easily snipped off by hydrolysis when required for respiration
What is amylase and glucosidase function?
Amylase - hydrolyses 1-4 glycosidic linkages
Glucosidase - responsible for hydrolysing 1-6 glycosidic linkages
What does it mean if polysaccharides are less soluble in water than monosaccharides?
If many glucose molecules dissolve in the cytoplasm the water potential would reduce and excess water diffuses in - disrupts the workings of the cell
Why are polysaccharides less soluble in water?
- Size
- Regions which could hydrogen bond with water are hidden away inside the molecule
What are lipids?
- Macromolecules
- Non polar
- Insoluble in water
- Dissolve in organic solvent like ethanol
- hydrophobic
How are triglycerides formed?
They are formed via the condensation between one glycerol and 3 molecule sof fatty acids
What is the structure of phospholipids
They are made of a glycerol molecule, two fatty acid chains and a phosphate group (attached to the glycerol). The 2 fatty acids also bond to the glycerol via two condensation reactions. This forms an ester bond
What is the phospholipid bilayer?
The phospholipids are positioned in a way that the hydrophilic head is exposed to the water and the tails are not.
This forms a phospholipid bilayer membrane structure which makes up the plasma membrane around cells.
What is cholesterol?
What is s sterol?
- It is a sterol
Sterols have 4 carbon rings and a hydroxyl group at one end and they have both hydrophobic and hydrophilic regions
What is the function of cholesterol?
It is embedded within cell membranes to impact fluidity
They help reduce the fluidity of membranes at high temperatures and increase fluidity at low temperatures
What is primary structure?
The sequence of amino acids in the polypeptide chain
What is secondary structure?
the sequence of amino acids causes parts of a protein molecule to bend into alpha helix or beta pleated sheets
* Held in place by hydrogen bonds
* Forms between the c=o groups of the carboxyl group of one amino acid and the H in the amine group of another amino acid
What is a globular protein?
- Polypeptide chains “roll up” into a spherical shape
- Relatively unstable structure
- soluble
- metabolic functions
e.g all enzymes like haemoglobin
What is tertiary structure?
The further folding of the secondary structure to form a unique 3D shape
* Held in place by ionic bonds. hydrogen bonds and disulphide bridges
* The ionic bonds and disulphide bridges form between the R groups of different ammino acids
* Disulphide bonds only sometimes occur, as there must be a sulfur in the R groups for this bond to occur
What is the quarternary structure?
A protein made up of more than one polypeptide chain
for example, haemoglobin
What is the importance of primary structure?
If even one amino acid in the sequence is different then it will cause the ionic/hydrogen/disulphide bonds to form in different locations
- Enzymes willl have a different shaped active site
- Carrier proteins will have different shaped binding site
What happens if a protein is denatured?
This means that bonds that hold the tertiary and secondary stucture in shape break and therefore the unique 3D shape is lost. (e.g enzymes losee their unique active site shape)
- Ionic and hydrogen bonds break
What is a fibrous protein?
- polyeptide chains form long twisted strands lined together
- Stable structure
- Insoluble in water
- Strength gives structural function
e.g collagen in the bone, keratin in the hair
What is the test for starch?
Iodine solution
Goes from brown to blue-black
What is the test for reducing sugars?
Benedict’s solution
1. Mix the sample with Benedict’s solution
2. Heat it with a water bath
Goes from blue to:
* Green at a low concentration of reducing sugars
* Yellow at a medium concentration of reducing sugars
* Brick red at a high concentration of reducing sugars
This is because the Cu2+ will be reduced to Cu+
What is the test for non reducing sugars?
- Boil is with hydrochloric acid
Hydrolyses sucrose to glucose and fructose which are reducing sugars - Use Benedict’s solution
- Heat it with a water bath
It will go from blue to:
* Green at a low concentration of reducing sugars
* Yellow at a medium concentration of reducing sugars
* Brick red at a high concentration of reducing sugars
What is the test for lipids?
Emulsion test
1. Mix ethanol with your sample and mix it with water
Dissolves the lipids in ethanol
* Positive test = white layer formed
What is the test for proteins?
Biuret’s solution
1. Mix sample with your solution for a few minutes
* Changes from blue to purple
- Set the filter in the colorimeter (picking the colour)
- Calibrate the machine using distilled water and seeing what absorbance of light there is
- Insert sample from biochemical test
- It measures the percentage transmission of light going through your sample
- Create a calibration curve using the results from known concentrations of glucose
What is the method for biosensors?
- A single strand of DNA or protein, which is complementary to the test sample, is immobilised. When the sample is added, it will bind to the immobilised DNA/Protein
- This binding causes a change in a tranducer and as a result, an electronic current is released
- This current is processed to determine the concentration of the sample present
What are microfibrils anad macrofibrils?
Cellulose chains form microfibrils which bundle together into macrofibrils which are embedded in pectins to form cell walls
Macrofibri;s run in all directions criss-crossing the wall for extra strength
Why is cellulose an excellent material for plant cell walls?
- Microfibrils and macrofibrils have very high tensile strength due to glycosidic bonds and hydrogen bonds between the chains
- Macrofibrils run in all directions, criss-crossing the wall for extra strength
- Difficult to digest cellulose because the glycosidic bonds are less easy to break
What are key features that help the plant cell wall to do its job?
- Plants do not have a rigid skeleton, each cell needs to have strength to support the whole plant
- Space between macrofibrils for water and mineral ions to pass on their way into and out of the cell. Makes the wall fully permeable
- Wall has high tensile strength, prevents plant cell from bursting when they are turgid, helping to support the plant
What is does unsaturated mean?
Double bond
- One or more changes the shape of the hydrocarbon giving it a kink where the double bond is
- Pushes the molecules apart slightly, it makes it more fluid
What are functions of triglycerides?
5x
- Energy store
- Energy source
- Insulation
- Buoyancy
- Protection
What is energy source?
Broken down in respiration to release energy and generates ATP
What is energy store?
Insoluble in water, they can be stored without affecting the water potential
One gram of fat releases twice as much energy as 1g of glucose - higher proportion of hydrogen atoms than carbs
What is insulation?
Adipose tissue is a storage location for lipid in whales, acting as a heat insulator
What is buoyancy?
Fat is less dense than water, used by aqautic mammals to hellp them stay afloat
What is protection?
Fat around delicate organs such as kidneys to act as a shock absorber
