3.1.1 BIOLOGICAL MOLECULES

What is the formula of glucose?

C6H12O6.

What is the effect of a C=C double bond in a unsaturated molecule?

C=C double bond causes bending, pushing the unsaturated triglyceride molecules further apart than the saturated molecules. This weakens the intermolecular forces between the unsaturated triglyceride molecules; form a liquid at room temperature.

What organic atoms are lipids made of?

CHO; carbon, hydrogen and oxygen

What organic atoms are carbohydrates made of?

CHO; carbon, hydrogen oxygen

What organic atoms are proteins made of?

CHON; carbon, hydrogen, oxygen, nitrogen

What organic atoms are nucleic acids made of?

CHONP; carbon, hydrogen, oxygen, nitrogen, phosphorus

What are organic molecules?

Carbon-containing molecules

How are polysaccharides formed?

formed by the condensation of many monosaccharides (above 2).

Why arent lipids (triglycerides) polymers?

they arent made out of many repeating monomers joined together but they are composites of different components.

A fatty acid may be represented by the chemical formula

(RCOOH). The R-group (hydrocarbon chain) may be either saturated or unsaturated.

What are saturated fatty acids?

(completely full of hydrogen), No C=C double bonds in hydrocarbon chain; all carbons fully saturated with hydrogen

Describe the benedict's test for non-reducing sugars:

- Add food sample to be tested to a test tube. If the sample is solid and not in liquid form, grind up in water and then filter out the solid. - Add a few drops of dilute hydrochloric acid (to hydrolyse disacharide/surcose to its constituent reducing sugars= monosacharides) - Heat in a boiling water bath - Cool solution and neutralise with sodium bicarbonate (alkali) as benedict's reagent wont work in acidic conditions - Test with pH paper that solution is alkaline. - Add benedict's reagent and heat again in boiling water bath - Non-reducing sugar present = green / yellow / orange / red precipitate. Stays blue = no sugar or carbohydrate.

Method to carry out Benedict's test for reducing sugars:

- Add food sample to be tested to a test tube. If the sample is solid and not in liquid form, grind up in water and then filter out the solid. - Add benedict's reagent (blue) to sample AND - Heat / boil mixture in water bath for 5 min - Positive = change from blue to green / yellow / orange / red precipitate (reducing sugar present).

Describe the iodine test for starch

- Add iodine dissolved in potassium iodide to solution and shake/stir - transition from browny-orange to blue-black colour = starch present.

Give examples of reducing sugars:

- All monosaccharides e.g. glucose - Some disaccharides e.g. maltose / lactose

Describe the structure of starch:

- Amylose structure has C1-C4 glycosidic bonds so is unbranched, long, helical, coiled. - Amylopectin structure has C1-C4 and C1-C6 glycosidic bonds so is branched, is long.

Describe the structure of starch relating to its function:

- Amylose: helical; compact for storage in cell, large polysaccharide molecule; can't leave cell. - Amylopectin: side branches increase SA and allow enzymes that breakdown the molecule to get at the glycosidic bonds easily to be rapidly hydrolysed, releasing glucose quickly. - BOTH insoluble in water; dont affect water potential i.e. no osmotic effect.

Describe what each colour of the benedict's test reveals about the concentration of sugar present

- BLUE: none - GREEN: very low - YELLOW: low - ORANGE: medium - RED: high

Describe the structure of cellulose related to its function. (Explain how cellulose molecules are adapted for their function in plant cells)

- Every other beta-glucose molecule (joined by condensation in 1:4) is inverted in a long, straight, unbranched chain. - Many hydrogen bonds link parallel chains of cellulose (crosslinks) to form microfibrils (strong fibres). H bonds are strong in numbers - Provides rigidty / strength and structural support to plant cell walls.

Describe the properties of triglycerides in relation to their structure:

- High ratio of C -H bonds to C atoms in hydrocarbon tail (long polymers), so release more energy than the same mass of carbohydrates - Non-polar, Insoluble in water , so no effect on water potential of cell --> no affect on osmosis

Give examples of non-reducing sugars

- No monosaccharides - Some disaccharides e.g. sucrose

Describe the the structure of phospholipids in relation to their function:

- Phosphate heads are polar / hydrophilic, So are attracted to water → orient to aqueous environment either side of membrane (face outwards) - Fatty acids 'tail' are non-polar / hydrophobic, So are repelled by water → orient to interior of membrane (face inwards)→ repels polar / charged molecules (e.g. h2o)

What is the structural levels of proteins?

- Primary (1o) structure - Secondary (2o) structure - Tertiary (3o) structure - Quaternary (4o) structure

Describe the tertiary structure of proteins and the role of bonds:

- Way in which overall (protein) is folded making the final 3D structure/resting shape of a polypeptide - held together by interactions between amino acid side chains: Peptide bond, Ionic bonds / disulfide bridges / hydrogen bonds

What are unsaturated fatty acids?

- in refrence long hydrocarbon chains (fatty acids) - the hydrocarbon chain contains one or more C=C double bonds between carbons in fatty acid Poly-unsaturated: more than one double bond between carbon atoms

Describe the secondary structure of proteins and the role of bonds:

- long chains of amino acids (polypeptides) fold or curl into regions with repeating patterns: alpha-helix; coiled and beta-pleated sheets; zig-zag - Hydrogen bonding between amino acids (between carboxyl O of one and amino H of another) - peptide bonds present

Examples of monomers are:

- monosaccharides - amino acids - nucleotides (polymer is DNA / RNA)

What is the role of lipids:

- plasma membranes, - energy source / store - buoyancy - waterproofing (insoluble in water), - insulation, protection (for delicate organs).

Describe the structure of glycogen related to its function:

- very Branched; big SA, can be rapidly hydrolysed to release glucose for respiration to provide energy quickly - Large polysaccharide molecule; cant leave cell - Insoluble in water; water potential of cell not affected ie no osmotic effect.

What is a dipeptide / how is it formed?

2 amino acids joined together by a condensation reaction in forming a peptide bond between the amine (NH2) group and the carboxylic (COOH) group of adjacent amino acid

____ amino acids are common in all organisms - differ only in their _______ group

20, R (side) group

What is a reducing sugar

A sugar that can donate electrons to another chemical

Describe the function of a phospholipid:

Form a bilayer in cell membrane, allowing diffusion of non-polar / small molecules membrane = (control the entry and exist of substances in and out of the cell)

Describe the emulsion test for lipids (must state steps in order for full marks)

If solid grind first 1. Add equal volume ethanol (alcohol) and shake/mix/stir (dissolves lipids in alcohol) 2. Then add equal volume water after 3. Positive: forms milky/white cloudy emulsion layer

Describe the formation of a phospholipid.

One of the fatty acids of a triglyceride is substituted by a phosphate-containing group, forming a phosphate ester bond. (so 2 fatty acids, 1 glycerol, 1 phopshpate group)

What are isomers?

Organic molecules with same molecular formula but differently arranged atoms / structural formula

Describe the primary structure of proteins and the role of bonds:

Sequence of amino acids in polypeptide chain (peptide bond)

What is a starch?

Starches are a polysaccharide composed of a mixture of amylose and amylopectin, formed by the condensation of alpha-glucose.

What is condensation?

The joining together of 2 molecules (monomers) forming a larger molecule, a chemical bond (e.g. glycosidic bond) and the elimination of a water molecule.

Monosaccharides

The monomers from which larger carbohydrates are made

What are the two groups of lipids?

Triglycerides and phospholipids

What is the difference in structures of alpha and beta glucose?

alpha OH group is below C1 but in beta-glucose it is above C1. (hydroxyl groups and H hydrogen on right hand side reversed) (TIP: Alpha glucose: santa (HO HO) so HO both on the bottom same position)

What are the two isomers of glucose?

alpha glucose and beta glucose

What is the monomer of a protein?

amino acids (20)

Lysis:

breaking down

How are disaccharides formed?

by the condensation of two monosaccharides, in this reaction a glycosidic bond forms between the two monosaccharides and a molecule of water is released.

Name all of the organic atoms.

carbon, hydrogen, nitrogen, oxygen, phosphorus

Protein shape is very specific to its function = change of shape →

change of function

The range of colour of the precipitate follows according to the __________

concentration

How is cellulose formed?

condensation of beta glucose only (glycosidic bonds)

The different structures of saturated triglycerides, unsaturated triglycerides and phospholipids result in ______________ in living organisms.

different properties and different functions

Describe the function of triglycerides:

energy storage molecule

What is the function of starch?

energy store in plant cells for respiration

A condensation reaction between glycerol and fatty acid (RCOOH) forms an.....

ester bond

In a triglyceride it forms 3.....

ester bonds

How is sucrose (disaccharide) formed?

formed from an alpha-glucose molecule and a fructose molecule joined in a condensation reaction

How is lactose (disaccharide) formed?

formed from an alpha-glucose molecule and galactose molecule joined in a condensation reaction

How is maltose (disaccharide) formed?

formed from two alpha-glucose molecules joined in condensation reaction

Describe the function of glycogen.

glucose / energy store in animal cells.

Common monosaccharides are:

glucose, fructose and galactose

What is the polysaccharide present in animal cells

glycogen

Two monosaccharides may join by condensation to form a...

glycosidic bond

What is glucose?

hexose (6-carbon) sugar

When talking about hydrolysis, we can say the molecule is being ___________.

hydrolysed

Polysaccharides can be broken down into their constituent disaccharides or monosaccharides by ___________ ____________

hydrolysis reactions

How are triglycerides formed?

in a series of 3 condensations of 1 molecule of glycerol and 3 fatty acid molecules (RCOOH), forming 3 ester bonds. Glycerol loses one hydrogen and fatty acid loses a hydroxide group per ester bond made.

As polysaccharides are very large molecules, they are usually __________. This makes them suitable for ____________.

insoluble, storage

What are polymers?

large molecule made up of many smaller identical monomers/molecules joined together

Draw a beta glucose molecule

look at image

Draw an alpha glucose molecule

look at image

Draw the structure of an amino acid

look at picture

Name three examples of disaccharides.

maltose, sucrose, lactose

What is a polypeptide / how is it formed?

many amino acids joined together by condensation / polymerisation

What is a fibrous protein?

many polypeptide chains are twisted together, has structural functions (e.g. collagen)

Carbohydrates can be classified into three groups:

monosaccharides, disaccharides and polysaccharides

Sucrose is a ________ sugar

non-reducing

Describe hydrogen bonds

numerous but easily broken

A condensation reaction between 2 amino acids forms a

peptide bond

Most carbohydrates, proteins and nucleic acids are _____________

polymers

Describe the structure of glycogen.

polysaccharide of alpha glucose with C1-C4 and C1-C6 glycosidic bonds so very branched

EXAM TIP 2:

proteins have a variety of functions within all living organisms. You need to be able to relate the structure of proteins to properties of proteins named throughout the specification e.g. enzymes/antibodies

What is the function / role of cellulose?

provides strength and structural support / rigidity to plant cell walls, prevents bursting of cell

Monosaccharides and disaccharides are...

simple carbohydrates (sugar)

What is a trace when describing concentration of sugar?

small amount of sugar

What are monomers?

smaller repeating unit / molecule from which many can be joined together to form a polymer / larger molecule

What is a percipitate

solid particles suspended in a solution

Describe the quaternary structure of proteins and the role of bonds:

specific 3D shape of protein made from more than 1 polypeptide chain joined together (e.g. haemoglobin) - Held together by more peptide, hydrogen, ionic and disulfide bonds

What are the polysaccharides in plants (THAT ARE NEVER FOUND IN ANIMAL CELLS).

starch (2 types), cellulose

What are the three main polysaccharides?

starch (amylose and amylopectin), glycogen, cellulose

Describe disulfide bonds

strong

Some polysaccharides like cellulose are not used for storage but give _______________ ______________.

structural support

Saccharide

sugar

What is hydrolysis?

the breaking / hydrolysing of the chemical bond (be specific e.g glycosidic) between two molecules (monomers) in a reaction by the addition of a water molecule, producing two monomers

Exam tip:

to get full marks for a diagram of a condensation or hydrolysis reaction, you need to include the H2O molecule that is added or removed.

In a phospholipid bilayer, the hydrophilic heads form _____ ____ on the outside while the hydrophobic tails are.....

two rows, sheltered in the middle

What is a globular protein?

usually fewer polypeptide chains with spherical shape, metabolic functions (e.g. enzymes, haemaglobin)

Hydrate

water

Lipids are insoluble in ________ but soluble in...

water, organic solvents e.g. alcohols and acetone.

Describe ionic bonds

weaker than disulfide and easily broken by changes in pH

EXAM TIP:

when describing the structure of polysaccharides, always be specific whether you're talking about alpha-glucose or beta-glucose, or else you won't get a mark for just saying glucose.