Chromosomes, Genes and DNA

Question 1

What is heterochromatin?

Answer 1

Chromatin which is packed tightly and is not being read.

Question 2

What is the beads on a string model?

Answer 2

DNA is wound around histone cores, in an arrangement that looks like beads on a string.

Question 3

What is the difference between a major and minor groove of DNA? Why do these arise?

Answer 3

DNA is a flexible molecule, no due to the nature of the helix there are two different grooves. Minor grooves are the flexible grooves. These arise due to the asymmetrical nature of the molecules.

Question 4

What is a nucelosome?

Answer 4

It is a histone core with its DNA wound around it.

Question 5

The beads on a string in DNA are tightly packed into another structure. What is this called?

Answer 5

Solenoid.

Question 6

How do solenoids form chromosomes?

Answer 6

Solenoids form loops and are tightly packed into chromosomes. In chromosomes, DNA cannot be read.

Question 7

What is the difference between a nucleotide and a nucleoside?

Answer 7

A nucleoside contains a base and a sugar. An nucleotide contains both of these and a phosphate molecule.

Question 8

What is the difference between RNA and DNA (in terms of the molecules they are composed from)?

Answer 8

DNA is composed from deoxyribose sugars. These only have one OH group. RNA is composed of ribose sugars which each have 2 OH groups.

Question 9

What is the difference between a purine and a pyrimidine?

Answer 9

Purines have a double ringed aromatic structure whilst pyrimidine only have a single ringed structure.

Question 10

Which sugars are purines?

Answer 10

Adenine, guanine.

Question 11

Is cytosine a purine or a pyrimidine?

Answer 11

Pyrimidine

Question 12

Is thymine a purine or a pyrimidine?

Answer 12

Pyrimidine

Question 13

Is adenine a purine or a pyrimidine?

Answer 13

Purine.

Question 14

What is uracil?

Answer 14

Uracil is a pyrimidine which is only found in RNA not DNA instead of thymine.

Question 15

RNA/DNA are polymers. What kind of bond connects each individual subunit?

Answer 15

Phosphodiester bond.

Question 16

How do DNA bases pair and how many hydrogen bonds do they form?

Answer 16

Guanine pairs with cytosine with 3 hydrogen bonds.

Adenine pairs with Thymine with 2 hydrogen bonds.

Question 17

What is an RNA stem loop?

Answer 17

This is where there are 2 anti parallel RNA sequences on the same molecule and they come together due to their complementary nature and form a loop.

Question 18

What is the conventional direction for writing DNA sequences?

Answer 18

5 prime to 3 prime.

Question 19

What is meant by DNA replication being a semi conservative method?

Answer 19

This means that one strand is maintained and used as a template.

Question 20

During replication, in which direction does the new strand grow?

Answer 20

At the three prime end. This is where new nucleotides are added.

Question 21

What is the name of the enzyme which catalyses addition of nucleotides to the DNA strand?

Answer 21

DNA polymerase

Question 22

What substance is needed to initiate DNA replication?

Answer 22

Primase. This kick starts the reaction.

Question 23

What is the definition of the leading strand in DNA replication?

Answer 23

The leading strand is the strand which can be built continuously from 5prime to 3prime. The other strand is the lagging strand and this must be built in fragments.

Question 24

What enzyme joins the fragments on the lagging strand in DNA replication?

Answer 24

DNA ligase

Question 25

What is DNA Helicase?

Answer 25

This is the enzyme which unwinds the DNA molecule so that it can be replicated.

Question 26

Where does DNA replication start?

Answer 26

It starts in many different places on the molecule and this produces multiple replication forks.

Question 27

How does the definition of a chromosome change before and after replication?

Answer 27

Before replication one chromosome contains one strand of DNA but after replication one chromosome contains two strand of DNA.

Question 28

What is found at the centre of a chromosome?

Answer 28

Centromere. It connects the chromatids and acts as a site which the spindle can attach to in cell division.

Question 29

What is the difference between mitosis and meiosis?

Answer 29

Mitosis produces two identical daughter cells whilst meiosis produces four non identical daughter cells.

Question 30

What two processes occur during Telophase?

Answer 30

The nuclear membrane forms and the cell cleaves.

Question 31

What is the name of the phase in the cell cycle where the nuclear membrane disintegrates?

Answer 31

Prophase

Question 32

What happens at Anaphase?

Answer 32

Chromosomes are separated to the poles of the cell, and the spindle retracts.

Question 33

What is the name of the phase in the cell cycle where the chromosomes are lined up in the centre of the cell?

Answer 33

Metaphase

Question 34

What is the difference between the lining up of chromosomes in metaphase in meiosis and mitosis?

Answer 34

In mitosis they line up randomly whereas in meiosis they line up as homologous pairs.

Question 35

In which phase of the cell cycle does crossing over and recombination of chromosomes in meiosis occur?

Answer 35

Prophase 1.

Question 36

What is random assortment of chromosomes?

Answer 36

This is where in anaphase 1 during meiosis it is random which chromosome which chromosome from each homologous pair goes to each pole and therefore increases variation.

Question 37

In oogenesis, how many eggs are produced from one oocyte?

Answer 37

1.

Question 38

What is the difference between genotype and phenotype?

Answer 38

Genotype is genetic information carried by the pair of alleles which determines a characteristic. Phenotype is the interaction of this with the environment which produces observable characteristics.

Question 39

Define hemizygous.

Answer 39

This is where a person only has one allele for a gene because it is found on the X chromosome in males.

Question 40

How is a person described if they have 2 identical alleles for a gene?

Answer 40

They are a homozygous. Their alleles are homozygous.

Question 41

What does Heterzygous mean?

Answer 41

This means that two different alleles for the same gene are present.

Question 42

If a disorder is autosomal, what does this mean?

Answer 42

It means that the mutant allele is on a gene which is not a sex chromosome.

Question 43

What type of genetic disorder is one which does not affect Heterzygotes and requires both parents to be at least carriers in order for the possibility of affected offspring?

Answer 43

Autosomal recessive.

Question 44

What effect will an X linked recessive disorder on a male or a female?

Answer 44

It will only affect a female if she is homozygous for the affected allele. It will always affect a male.

Question 45

What type of people will be affected by an autosomal dominant condition?

Answer 45

Heterzygotes.

Question 46

What is co-dominance?

Answer 46

Co-dominance is where there is not one allele which is dominant over another, but instead both alleles contribute to the phenotype - for example in blood groups.

Question 47

What are linked genes?

Answer 47

Linked genes are genes which are found close together on a chromosome and this means that they are unlikely to be separated by crossing over and recombination.

Question 48

Explain why it is possible for two affected individuals to produce normal offspring.

Answer 48

Often, more than one gene is responsible for a phenotype. This is called complementation. Each gene is responsible for an enzyme which determines product formation.

Question 49

What is the name for chromatin which is being actively transcripted?

Answer 49

Euchromatin