Flashcards in Chromosomes, Genes and DNA Deck (49):
What is heterochromatin?
Chromatin which is packed tightly and is not being read.
What is the beads on a string model?
DNA is wound around histone cores, in an arrangement that looks like beads on a string.
What is the difference between a major and minor groove of DNA? Why do these arise?
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.
What is a nucelosome?
It is a histone core with its DNA wound around it.
The beads on a string in DNA are tightly packed into another structure. What is this called?
How do solenoids form chromosomes?
Solenoids form loops and are tightly packed into chromosomes. In chromosomes, DNA cannot be read.
What is the difference between a nucleotide and a nucleoside?
A nucleoside contains a base and a sugar. An nucleotide contains both of these and a phosphate molecule.
What is the difference between RNA and DNA (in terms of the molecules they are composed from)?
DNA is composed from deoxyribose sugars. These only have one OH group. RNA is composed of ribose sugars which each have 2 OH groups.
What is the difference between a purine and a pyrimidine?
Purines have a double ringed aromatic structure whilst pyrimidine only have a single ringed structure.
Which sugars are purines?
Is cytosine a purine or a pyrimidine?
Is thymine a purine or a pyrimidine?
Is adenine a purine or a pyrimidine?
What is uracil?
Uracil is a pyrimidine which is only found in RNA not DNA instead of thymine.
RNA/DNA are polymers. What kind of bond connects each individual subunit?
How do DNA bases pair and how many hydrogen bonds do they form?
Guanine pairs with cytosine with 3 hydrogen bonds.
Adenine pairs with Thymine with 2 hydrogen bonds.
What is an RNA stem loop?
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.
What is the conventional direction for writing DNA sequences?
5 prime to 3 prime.
What is meant by DNA replication being a semi conservative method?
This means that one strand is maintained and used as a template.
During replication, in which direction does the new strand grow?
At the three prime end. This is where new nucleotides are added.
What is the name of the enzyme which catalyses addition of nucleotides to the DNA strand?
What substance is needed to initiate DNA replication?
Primase. This kick starts the reaction.
What is the definition of the leading strand in DNA replication?
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.
What enzyme joins the fragments on the lagging strand in DNA replication?
What is DNA Helicase?
This is the enzyme which unwinds the DNA molecule so that it can be replicated.
Where does DNA replication start?
It starts in many different places on the molecule and this produces multiple replication forks.
How does the definition of a chromosome change before and after replication?
Before replication one chromosome contains one strand of DNA but after replication one chromosome contains two strand of DNA.
What is found at the centre of a chromosome?
Centromere. It connects the chromatids and acts as a site which the spindle can attach to in cell division.
What is the difference between mitosis and meiosis?
Mitosis produces two identical daughter cells whilst meiosis produces four non identical daughter cells.
What two processes occur during Telophase?
The nuclear membrane forms and the cell cleaves.
What is the name of the phase in the cell cycle where the nuclear membrane disintegrates?
What happens at Anaphase?
Chromosomes are separated to the poles of the cell, and the spindle retracts.
What is the name of the phase in the cell cycle where the chromosomes are lined up in the centre of the cell?
What is the difference between the lining up of chromosomes in metaphase in meiosis and mitosis?
In mitosis they line up randomly whereas in meiosis they line up as homologous pairs.
In which phase of the cell cycle does crossing over and recombination of chromosomes in meiosis occur?
What is random assortment of chromosomes?
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.
In oogenesis, how many eggs are produced from one oocyte?
What is the difference between genotype and phenotype?
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.
This is where a person only has one allele for a gene because it is found on the X chromosome in males.
How is a person described if they have 2 identical alleles for a gene?
They are a homozygous. Their alleles are homozygous.
What does Heterzygous mean?
This means that two different alleles for the same gene are present.
If a disorder is autosomal, what does this mean?
It means that the mutant allele is on a gene which is not a sex chromosome.
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?
What effect will an X linked recessive disorder on a male or a female?
It will only affect a female if she is homozygous for the affected allele. It will always affect a male.
What type of people will be affected by an autosomal dominant condition?
What is co-dominance?
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.
What are linked genes?
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.
Explain why it is possible for two affected individuals to produce normal offspring.
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.