3.1.1 Biological Molecules Flashcards
What is a polymer?
Molecule made of large number of monomers joined together
What are monomers?
Small, basic molecular units
Name the 3 elements all carbohydrates contain
C, H & O
What are the monomers in carbohydrates?
Monosaccharides
(e.g. glucose, fructose, galactose)
What type of sugar is glucose?
Hexose sugar (monosaccharide with 6 carbon atoms in each molecule)
Name the 2 types of glucose
alpha (α) & beta (β)
Draw the skeletal structure for α-glucose
Draw the skeletal structure for β-glucose
In alpha glucose the OH is…
below the plane of the ring
In beta glucose the OH is…
above the plane of the ring
What is a condensation reaction?
Joining together of molecules with a chemical bond & the elimination of a water molecule (it’s released)
How are monosaccharides joined together?
By condensation reactions
What type of bond is formed between the 2 monosaccharides as molecule of water is released?
A glycosidic bond
What is formed when 2 monosaccharides join together?
A disaccharide
How is sucrose formed?
Formed from condensation reaction between α-glucose molecule and fructose molecule
What is lactose formed from?
From glucose molecule & galactose molecule
What is maltose formed from?
From 2 α-glucose molecules
What is hydrolysis?
Breaking of the chemical bond between monomers using a water molecule
When are polysaccharides formed?
When more than 2 monosaccharides are joined together by condensation reactions
Where is starch located in organisms?
Many parts of plants in the form of small grains + large amounts found in seeds & storage organs
What is the purpose of starch?
Plants store excess glucose as starch
How is starch produced?
Condensation of many α-glucose sub units, which then form hydrogen bonds with molecules in the same chain
Starch is a mixture of…
2 polysaccharides of alpha-glucose
Name the 2 polysaccharides of alpha-glucose found in starch
- Amylose
- Amylopectin
Describe the structure of amylose
Long, unbranched chain of α-glucose
Describe how the structure of amylose relates to its function
Angles of the glycosidic bonds = coiled structure → makes it compact = can fit more into a small space (= good for storage)
Describe the structure of amylopectin
Long, branched chain of α-glucose
Describe the structure of amylopectin relates to its function
Its side branches allow the enzymes that break down starch to get at the glycosidic bonds easily = glucose can be released quickly
α-glucose molecules are formed by what type of glycosidic bonds?
1,4 & 1,6 glycosidic bonds
Where is glycogen located in organisms?
Stored as small granules mainly in liver and some in muscles
What is the purpose of glycogen?
In animals: excess glucose is stored as glycogen
Glycogen is a p______…
Polysaccharide of α-glucose
Describe glycogen’s structure
Very similar to amylopectin BUT has lots more side branches coming off it + shorter chains
Describe how glycogen’s structure relates to its function
- Loads of branches & shorter chains = stored glucose can be released even quicker than in starch → important for energy releases in animals
- Very compact molecule, making it good for storage
Why is starch suited for its role? 3x
- Insoluble in water = doesn’t affect water potential (doesn’t cause water to enter cells by osmosis)
- Compact = lots of it can be stored in small space
- When hydrolysed, alpha glucose can be easily transported & used in respiration
Describe the test for starch
- Add iodine dissolved in potassium iodide solution to test sample
- If starch present = sample changes from browny-orange to blue-black colour
(Carried out at room temp.)
Describe the structure of cellulose
- Long, unbranched chains of beta-glucose
- Straight cellulose chains run parallel to each other in cell walls = allows hydrogen bonds to form cross-linkages between chains
- Result: formation of bundles called micro fibrils which then join together to make macro fibrils
What is the purpose of cellulose?
To provide rigidity to plant cells
How does cellulose prevents the cell from bursting as water enters it by osmosis?
By exerting inward pressure that stops any influx (inrush) of water = makes plant cells turgid
Why is it important that stems & leaves are in a turgid state?
To provide maximum surface area for photosynthesis
Name the 2 types of sugars
Reducing and non-reducing
What is a reducing sugar?
Sugars that can donate electrons to another chemical e.g. Benedict’s reagent
i.e. all monosaccharides and some disaccharides (e.g. maltose and lactose)
Describe Benedict’s test for reducing sugars
- Add Benedict’s reagent (blue) to sample & heat it in water bath that’s been brought to a boil (for 5 mins)
- Test’s positive = orange/red precipitate
- Higher the concentration of reducing sugar = further the colour change goes
Benedict’s Test for Reducing Sugars:
The colour of the precipitate changes from…
Benedict’s Test for Reducing Sugars:
What’s a more accurate way of comparing the amount of reducing sugar in different solutions (than colour change)?
Filter solution & weigh precipitate
What does it mean if the result of the reducing sugars test is negative (i.e. no precipitate is formed)?
Means a non-reducing sugar present (disaccharides)
Describe the test for non-reducing sugars
- Boil supernatant (new test sample) with dilute hydrochloric acid (in water bath)
- Then neutralise it with sodium hydrogencarbonate
- Check solution is alkaline (with pH paper)
- Carry out Benedict’s test as you would for a reducing sugar
- If test’s positive = orange/red precipitate
- If test’s negative = solution remains blue = no sugar present
In the test for non-reducing sugars, why is dilute hydrochloric acid added?
To hydrolyse, break down, the non-reducing sugar (disaccharide) into monosaccharides
Name 5 roles of lipids
- Energy source
- Flexibility in plasma membranes
- Protection
- Insulation
- Waterproofing
Elaborate on lipids’ role as a energy source
When oxidised, lipids = more than twice as much energy per gram as carbohydrates
Elaborate on lipids’ role in plasma membranes
Phospholipids contribute to flexibility of membranes & transfer of lipid-soluble substances across them
Elaborate on lipids’ role in protection
Stored around delicate organs
Elaborate on lipids’ role in insulation
Fats = slow conductors of heat = help retain body heat
Elaborate on lipids’ role in waterproofing
Lipids are insoluble in water ∴ waterproof material
- In plants & insects: waxy cuticle to conserve water
- In mammals: produce oil secretion from sebaceous glands in skin
Describe the structure of a triglyceride
One molecule of glycerol with 3 fatty acids attached to it
What do fatty acids have?
Have long ‘tails’ made from hydrocarbons
Properties in triglycerides differ due to variations in ___ __
fatty acids
Name 2 kinds of fatty acids
- Saturated
- Unsaturated
Draw a saturated fatty acid
Draw a unsaturated fatty acid
What does the double carbon bond causes the chain to do?
Causes it to kink
Define mono-unsaturated
Single double bond
Define polyunsaturated
More than one double bond
Describe how a triglycerides forms
- A fatty acid joins to a glycerol molecule
- When ester bond is formed = molecule of water is released - condensation reaction
- Process happens twice more = form a triglyceride
Why are triglycerides good energy storage molecules?
Long hydrocarbon tails of fatty acids contains lots of chemical energy = lot of energy released when they’re broken down
∴ contain twice as much energy per gram as carbohydrates
Describe how the structure of a triglyceride makes them insouble
- Triglycerides clump together as insoluble droplets in cells ∵ fatty acid tails = hydrophobic
- = tails face inwards = shielding themselves from water with their glycerol heads
Where are phospholipids found?
In cell membranes
Describe the structure of a phospholipid
One molecule of glycerol with 2 fatty acids + a phosphate group attached to it
Draw glycerol
Draw the basic structure of a fatty acid
Draw a triglyceride
Phospholipids: Phosphate group (the 'head') is \_\_\_\_\_\_\_
hydrophilic (attracts water)
Phospholipids:
Fatty acid tails is _______
hydrophobic (repel water)
Describe how phospholipids’ structures relates to its function
Phospholipids make up the bilayer of cell membranes
- Heads are hydrophilic & tails are hydrophobic = form double layer with their heads facing out towards the water on either side
- Centre of bilayer = hydrophobic = water-soluble substances can’t easily pass through
- Membrane acts as a barrier to those substances
Describe the emulison test for lipids
- Shake test substance with ethanol for few minutes so that it dissolves & then pour solution into water
- Any lipid will show up as a milky emulsion
- More lipid there is = more noticeable milky colour will be
What are the monomers in proteins?
Amino acids
What is formed when 2 amino acids join together?
Dipeptide
When is a polypeptide formed?
When more than 2 amino acids join together
Proteins are made up of one or more ____
polypeptides
What are 3 things all amino acids have? (structure wise)
- Carboxyl group (-COOH)
- Amine group (NH2)
- R group (aka variable side group)
All living things share bank of ___ amino acids
20
What changes with each amino acid?
The R group
What is glycine’s R group?
H
Draw an amino acid
How are polypeptides formed?
Formed by amino acids linking together by condensation reactions (molecule of water is released during reaction)
What is the name of the bond formed between amino
acids?
Peptide bonds
(Combines -OH from carboxyl group and -H from amino acid)
Draw a dipeptide
What is the primary structure in proteins?
Sequence of amino acids in polypeptide chain
What is the secondary structure in proteins?
- Hydrogen bonds form between amino acids in chain
- = makes it coil into alpha helix or fold into beta pleated sheet
What is the tertiary structure in proteins?
- Further folding of whole polypeptide chain
- More bonds form between different parts (R groups) of polypeptide chain:
- Hydrogen bonds
- Ionic bonds
- Hydrophobic interactions
- Disulphide bonds
Where do disulphide bonds form?
Between R-groups containing sulfur atoms
Where do ionic bonds form?
Form between R groups with charges
Describe hydrophobic interactions in proteins
When polypeptide chain folds:
- hydrophobic R-groups are in the interior of the folded chain
- whereas hydrophilic R-groups tend to be on the outside
What is the quaternary structure in proteins?
Arrangement of 2 or more polypeptide chains in a protein
For proteins made … the tertiary structure form their final 3D structure
proteins made from single polypeptide chain
For proteins made from … the quaternary structure is protein’s final structure
proteins made from more than one polypeptide chain (e.g. haemoglobin, insulin, collagen)
Describe the structure of an enzyme and a property of them
- Roughly spherical in shape due to tight folding of polypeptide chains
- Soluble (& often have roles in metabolism)
Describe the structure of antibodies
- Made up of 2 light (short) polypeptide chains & 2 heavy (long) polypeptide chains bonded together
- Have variable regions: amino acid sequences in these
regions vary greatly
Describe the structure of channel proteins (present in cell membranes) and its function
- Contain hydrophobic and hydrophilic amino acids = cause protein to fold up & form a channel
- These proteins transport molecules and ions across membranes
Why are structural proteins physically strong?
Consist of long polypeptide chains lying parallel to each other with cross-link between them
Describe the biuret test for proteins
- Test solution needs to alkaline ∴ add few drops of sodium
hydroxide solution - Then add some dilute copper(II) sulfate solution
- Protein present = turns purple
- No protein = solution stays blue
- (Colours are pale so look carefully)
Name the 2 types of proteins
Fibrous (strands) & Globular (spherical)
Give 3 examples of fibrous proteins
Structural:
collagen, muscles (actin & myosin), keratin
Give 3 examples of globular proteins
haemoglobin, enzymes, hormones, antibodies
What bond/interaction helps in the tertiary structure helps to form the 3D shape of globular proteins?
Hydrophobic interactions (keep circular shape - hydrophobic centre and hydrophilic outside)
