Biological molecules

Question 1

Draw the structure of an amino acid

Question 2

Draw the structure of a dipeptide

Answer 2

Peptide bonds

Question 3

How do you test for proteins?

Answer 3

Add biuret reagent, if the colour changes from blue to purple then a protein is present in the sample

Question 4

Define the primary structure of a protein

Answer 4

Sequence, number & type of amino acids in the polypeptide. Determined by sequence of codons on mRNA.

Question 5

Define the secondary structure of proteins

Answer 5

Forms localized hydrogen bonds between amino acids, forming two characteristic shapes: Alpha helix and Beta pleated sheet.

Question 6

Define the tertiary structure of a protein

Answer 6

Tertiary structure is the further folding of a polypeptide chain due to bonding between ‘R’ groups (hydrogen, ionic, disulphide bridges). This gives a specific 3D shape.

Question 7

Define the quaternary structure of a protein

Answer 7

A protein consisting of 2 or more polypeptide chains.

Question 8

Define the term denaturing

Answer 8

When hydrogen and ionic bonds are broken, changing the tertiary structure of the protein and so the active site changes shape.

Question 9

What is a nucleic acid?

Answer 9

Information carrying molecules, all polymers of nucleotides.

Question 10

Explain the differences between DNA and RNA?

Answer 10

RNA has ribose as their sugar and any one of the nitrogenous bases (adenine, guanine, cytosine, and uracil). DNA has deoxyribose as their sugar and any one of the following nitrogenous bases (adenine, guanine, cytosine, and thymine).

Question 11

What can RNA be found as?

Answer 11

mRNA, tRNA, rRNA.

Question 12

What is semi-conservative replication?

Answer 12

The process by which DNA copies itself and each new piece of DNA is made up of 1 old strand and 1 new strand.

Question 13

Explain the stages of DNA replication?

Answer 13

1) DNA helicase breaks the hydrogen bonds between polynucleotide strands, the double helix unwinds. 2) Bases are exposed and free DNA molecules bind to their complementary base pairs. 3) DNA polymerase joins new nucleotides together with phosphodiester bonds via a condensation reaction.

Question 14

What bonds are formed between phosphate and pentose sugars?

Answer 14

Phosphodiester bonds.

Question 15

What are the 5 properties of water and explain the benefits?

Answer 15

1) Metabolite - used in hydrolysis, made in condensation. 2) Good solvent - allows reactions to occur and substances dissolve in them. 3) High heat capacity - buffers a change in temperature. 4) Cohesive - gives surface tension/supports the column of water in the plant. 5) Large latent heat of vaporization - has a cooling effect as lots of energy is needed to turn liquid into vapor.

Question 16

Draw the structure of ATP

Question 17

Explain the process of ATP converting into energy?

Answer 17

1) ATP hydrolase will hydrolyse the bond between phosphate heads 2 + 3 leaving ADP and Pi. 2) This reaction releases lots of energy that can be used for other reactions within cells. 3) During photosynthesis and respiration, ATP synthase remakes ATP by the condensation of ADP + Pi.

Question 18

What is the importance of hydrogen ions?

Answer 18

The higher the concentration of the H+ the lower the pH; enzyme reactions rely on the maintenance of pH levels.

Question 19

What is the importance of iron?

Answer 19

Found in hemoglobin, iron binds to O2 to allow transportation around the body.

Question 20

What is the importance of sodium ions?

Answer 20

Used in co-transport of glucose and amino acids.

Question 21

What is the importance of phosphate ions?

Answer 21

Found in nucleotides and ATP.

Question 22

What is a polymer?

Answer 22

Large, complex molecules composed of long chains of monomers joined together. Insoluble and act as storage molecules.

Question 23

What are the 3 monosaccharides?

Answer 23

Glucose, hexose, pentose.

Question 24

Draw the structure of alpha glucose?

Question 25

Draw the structure of beta glucose?

Question 26

What are the 3 disaccharides?

Answer 26

Maltose - glucose + glucose, sucrose - glucose + fructose, lactose - glucose + galactose.

Question 27

What bond joins disaccharides together?

Answer 27

Glycosidic bonds formed in a condensation reaction.

Question 28

What is the structure of starch?

Answer 28

- Found as small grains in the chloroplast. - Alpha glucose. - Amylose - long unbranched high storage capacity. - Amylopectin - branched so large SA for enzymes to release sugars for respiration.

Question 29

What are the roles of starch?

Answer 29

- Energy store. - Insoluble - doesn't affect water potential of a cell. - Large - cannot diffuse. - Compact. - Branched.

Question 30

What is the structure and roles of glycogen?

Answer 30

- Alpha glucose found within animal cells. - Shorter chains/more branched - more enzymes act upon it, more glucose released for respiration - animals have a higher metabolic rate. - Insoluble. - Compact.

Question 31

What is the structure and properties of cellulose?

Answer 31

- Beta glucose. - Straight unbranched chains. - Parallel to each other. - Each glucose is inverted. - There are hydrogen bonds between the microfibrils which increase strength and rigidity and so give the cell wall structure.

Question 32

Draw the structure of triglycerides?

Question 33

What makes a triglyceride unsaturated?

Answer 33

Double C=C bond; liquid at room temperature.

Question 34

Draw the structure of a phospholipid?

Question 35

What are the properties of phosphate heads?

Answer 35

Polar (charged) and hydrophilic (water loving).

Question 36

What are the properties of the fatty acid tails?

Answer 36

Nonpolar (uncharged) and hydrophobic (water fearing).

Question 37

What is an enzyme?

Answer 37

It is a biological catalyst, meaning they speed up the rate of chemical reactions by reducing the activation energy but are not used within the reaction.

Question 38

What is the induced fit theory?

Answer 38

Enzyme and substrate are almost complementary but when the substrate enters the active site, interactions between the substrate and amino acids cause the shape of the active site to change slightly to become complementary. The tertiary structure of the active site changes.

Question 39

What happens when concentration increases on the rate of reaction?

Answer 39

As you increase substrate concentration, you increase the rate of reaction as more successful collisions are likely. Substrate concentration is limiting. When it plateaus, the substrate concentration is no longer limiting as increasing it does not increase the rate of reaction. The enzyme concentration may be limiting as all active sites are in use.

Question 40

What is a competitive inhibitor?

Answer 40

Similar shape to substrate; they fit into the enzyme active site temporarily, blocking access of substrate. Have little effect on high substrate concentration.

Question 41

What is a non-competitive inhibitor?

Answer 41

They are complementary to an allosteric site on the enzyme. It changes the tertiary structure of the active site so it's no longer complementary.