2. Biological functions Part 1

Question 1

Why do we need proteins?

Answer 1

• Are essential for all cells involved in virtually every single process
• Many different types of proteins which are specialised for different jobs

Question 2

List 6 of the protein functions:

Answer 2

• Transport
• Structural
• Internal defense
• Movement
• Regulation
• Catalytic

Question 3

What are proteins made of?

Answer 3

Amino acids, in which useful proteins are ‘Lego blocks’ with 20 different types of building blocks (amino acids).

Question 4

List the 3 basic structures of amino acids:

Answer 4

• Anime group
• R group
• Carboxylic acid group

Question 5

Describe the structure of amino acids?

Answer 5

• Each amino acid has a different R group with different chemical properties (Eg. Polar, non-polar, or charged)
• The different properties of amino acids help them to fold into correct shapes (Eg. Hydrophobic amino acids will always try to be as far away from the watery cytosol as possible)

Question 6

What is the amino acid to protein level determined by?

Answer 6

Are determined by the DNA sequence of the gene

Question 7

Describe the primary structure of a protein (level 1):

Answer 7

The sequence of amino acids in the polypeptide chain which are joined together by peptide bonds in a condensation reaction.

Question 8

Describe the secondary structure of a protein (level 2):

Answer 8

The peptide chain forms different coils or folds.

• a- Helices (tight coils)
• B- Sheets (fat folded sheets)

Question 9

Describe the tertiary structure of a protein (level 3):

Answer 9

The overall 3D shape of the protein, which is maintained by different bonds (Hydrogen bonds, ionic bonds, disulphide bridges), where the shape of the protein determines its function.

Question 10

Describe the quaternary structure of a protein (level 4):

Answer 10

Where the protein joins to more than one polypeptide chain, where different bonds (Eg. Hydrogen, ionic) hold the different chains together.

Question 11

Describe the protein structure (final level):

Answer 11

The overall structure is determined by the primary structure (order of amino acids), where changes to the primary structure also cause changes to the secondary, tertiary and quaternary structures.

Question 12

Describe the structure of DNA:

Answer 12

• Is a double stranded molecule
• In nucleotides join along the sugar/phosphate backbone by a phosphodiester bond
• Nitrogen bases join to their complementary bases (A to T, G to C via hydrogen bonds)
• The two backbones of DNA run in the opposite direction (anti-parallel)

Question 13

What is the function of DNA?

Answer 13

To store information

Question 14

What is the location and form of DNA in prokaryotes?

Answer 14

• Located in cytosol

- Made up of one singular chromosome and sometimes small extra pieces of DNA called plasmids

Question 15

What is the location and form of DNA in eukaryotes?

Answer 15

• Located in the nucleus, mitochondria, and chloroplasts.
• Come in the form of linear pairs of chromosomes in the nucleus, single circular chromosomes in mitochondria and chloroplasts

Question 16

Describe how proteins are involved in internal defense and give an example:

Answer 16

Antibodies (or immunoglobulins) are ‘Y’ shaped proteins that protect the body by identifying and killing disease-causing organisms such as bacteria and viruses.
Eg. Antibodies which destroy disease-causing organisms growing in the gut an airways.

Question 17

What is a proteome?

Answer 17

All the proteins created by a cell, tissue or an organism, which is complicated to study (The study of proteomes is called proteomics) since one protein can impact many hundreds of other proteins both directly and indirectly.

Question 18

What are 2 ways which enable us to know what proteins look like?

Answer 18

• X-ray crystallography

- Computer modelling (supercomputers, using crow sourced computers to process data, and ‘Gamifying’ folding)

Question 19

List the 4 differences between DNA and RNA:

Answer 19

• DNA has deoxyribose sugar, while RNA has ribose sugar
• DNA is double-stranded, while RNA is single-stranded
• DNA has a T base, while RNA has a U base
• DNA molecules are much longer than RNA molecules

Question 20

Why can the genetic code be described as degenerate?

Answer 20

Because most amino acids can be coded for by 2 or more codons

Question 21

What are codons?

Answer 21

Consist of 3 nucleotides, where each codon codes for a specific amino acid

Question 22

What are globular proteins? Give some examples:

Answer 22

Proteins that have a tertiary structure.

Eg. Enzymes and antigens

Question 23

What are fibrous proteins? Give some examples:

Answer 23

Proteins that have a primary and secondary structure, but not a tertiary structure.
-Are just long proteins
Eg. Keratin in hair and Actin in muscle fibres

Question 24

What is a locus?

Answer 24

The position of each of the genes on a chromosome.

Question 25

What is the structure of chromosomes composed of?

Answer 25

DNA and proteins called histones.

-Collectively this combination of nucleic acid and proteins is called chromatin

Question 26

Explain the specific importance of lac I gene in the lac operon and how the presence of lactose effects transcription:

Answer 26

• The lace I gene codes for the production of a repressor protein (that regulates the expression of the enzymes required for lactose breakdown).
• When lactose is present, it binds to the repressor protein, preventing the repressor protein from binding to the operator region, therefore allowing transcription of the genes coding for the enzymes.

Question 27

What is an operon? Give an example:

Answer 27

A functioning unit of DNA containing a cluster of genes under the control of a single promoter.
Eg. The lac operon consists of structural genes that produce 3 enzymes needed to process lactose (milk sugar).

Question 28

Describe the process of the lac operon:

Answer 28

• RNA polymerase would normally recognise and bind to the promoter region
• In the absence of lactose, a repressor protein binds with the operator, effectively blocking RNA polymerase from binding and thus preventing transcription of the structural genes. The repressor is coded for by a regulatory gene.
• When lactose present, some is converted, in the cell, to allolactose. Allolactose binds to the repressor protein (at a different site than the one that binds to the operator). The change in the form of the repressor means it can no longer bind to the operator.
• The operator no longer prevents transcription
• All three structural genes are transcribed to an mRNA molecule
• When lactose is no longer present, the repressor returns to its initial form and once again binds with the operator to prevent transcription.