Collinearity of Genes & Protein

Question 1

How many genes usually encode for each protein?

Answer 1

One.

Question 2

What is the central dogma of molecular biology?

Answer 2

DNA (genes) - mRNA- protein - function - cell / organism.

Question 3

Information flows from DNA to RNA to make proteins. Can this be reversed.

Answer 3

Not usually, no. It is a unidirectional flow of information.

Question 4

The DNA sequence corresponds to the amino acid sequence. True or false?

Answer 4

True.

Question 5

…………….. are joined into ……………… chains, which are folded to make proteins. There are an average of 500-1,000 ……………. in every protein.

Answer 5

Amino acids, polypeptide, amino acids.

Question 6

All amino acids have the same structure, apart from ………………… .

Answer 6

The R group.

Question 7

What four atoms / molecules are bonded to the central carbon atom of an amino acid?

Answer 7

A hydrogen atom, an amino group (NH2), a carboxyl group (COOH) and an R group.

Question 8

How many different amino acids are found in living cells?

Answer 8

Twenty.

Question 9

What are the four categories of amino acids?

Answer 9

1. Neutral and non-polar (hydrophobic).
2. Neutral and polar (hydrophilic).
3. Acidic (negatively charged).
4. Basic (positively charged).

Question 10

Which category do these nine amino acids belong to?

Glycine, alanine, valine, leucine, isoleucine, methionine, phenylalanine, tryptophan and proline.

Answer 10

Neutral and non-polar.

Their R groups can be aliphatic (a mixture of hydrogen and carbon atoms) or aromatic (more complicated).

Question 11

Which category do these six amino acids belong to?

Serine, threonine, cysteine, tyrosine, aspargine, glutamine.

Answer 11

Neutral and polar.

The R groups of these amino acids are not charged but they can interact with water by hydrogen bonding.

Question 12

Which category do these two amino acids belong to?

Aspartate, glutamate.

Answer 12

Acidic.

Their R groups have a negative charge.

Question 13

Which category do these three amino acids belong to?

Lysine, arginine, histidine.

Answer 13

Basic.

Their R groups have a positive charge.

Question 14

Where in proteins are neutral, non-polar amino acids likely to be found and why?

Answer 14

They are often found in the centre of proteins because they are hydrophobic.

Question 15

The first evidence of how genes encode for specific proteins came from studies on which type of cells?

Answer 15

Red blood cells and haemoglobin.

Question 16

Haemoglobin is a ………………. made of two …………. and two …………….. polypeptide chains. In inherited anaemia, sufferers have an altered ………….. caused by ……………….-…………….. mutations following Mendelian Laws.

Answer 16

Tetramer, alpha, beta, globin, semi-dominant.

Question 17

When the mutation for sickle cell anaemia is homozygous, all of the haemoglobin is altered and the sufferer develops severe anaemia.

What happens if the sickle cell gene is heterozygous?

Answer 17

The sufferer will still have anaemia, but less severely, because only have of the beta-chains are altered. The haemoglobin is only partially defective.

Question 18

Why can having the heterozygous sickle cell anaemia gene sometimes be an advantage?

Answer 18

Parasites cannot live in the slightly altered red blood cells so the hereterozygous form of sickle cell anaemia confer resistance to malaria.

Question 19

In sickle cell anaemia, the sixth amino acid in haemoglobin specifically changes from glutamate to valine. Why is this change so drastic?

Answer 19

The change from glutamate to valine is a drastic one because glutamate is acidic, negatively charged and hydrophilic, whereas valine is neutral, uncharged and hydrophobic.

Question 20

What is a silent mutation?

Answer 20

A mutation which does not cause any damage or change to the amino acid produced.

Question 21

In the 1950s, Seymour Benzer isolated mutants of the trpA cistron in E.Coli, which allowed him to do what?

Answer 21

He mapped the positions of these mutations within the gene and compared them to the sequencing of the amino acids.

Tryptophan synthase (trpA) can be read in the same direction and with the same spacing as the corresponding amino acid sequence, which is evidence of collinearity.

Question 22

What are operons?

Answer 22

Operons are unique to microbes and keep their genome compact.

Question 23

More than one genetic mutation can affect the amino acid at a single position, BUT there can be recombination between the mutants. What does this prove?

Answer 23

That the original mutations must be at different nucleotide position - more than one nucleotide corresponds to each amino acid.

Question 24

How do four nucleotides (adenine, thymine, guanine and cytosine) encode for twenty different amino acids?

Answer 24

Each amino acid corresponds to a triplet of nucleotides - a codon.

Question 25

Which type of bond joins amino acids in a polypeptide chain? What sort of reaction is this and what is produced?

Answer 25

A peptide bond between the carboxyl group of one amino acid and the amino group of another amino acid. It is a condensation reaction and water is produced.

Question 26

The primary structure of a protein is determined by………….?

Answer 26

The sequence of amino acids in the polypeptide chain.

Question 27

Name two types of secondary protein structures.

Answer 27

Alpha helices and beta pleated sheets.

Question 28

Secondary protein structures are held together by weak ……………. bonds and ………………. interactions.

Answer 28

Hydrogen, electrostatic.

Question 29

The tertiary structure of a protein is formed by doing what to the polypeptide chain?

Answer 29

Folding it into a three-dimensional shape.

Question 30

Which level of protein structure can only occur with two or more polypeptides associated in multi-subunit proteins?

Answer 30

Quaternary structure.

Question 31

In collinearity, the number of nucleotides in the gene is …………………… to the number of amino acids in the protein.

Answer 31

Proportional.