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Flashcards in DNA Extra Deck (17):

Why is DNA known as a double helix?

It's two strands that run anti parallel to each other (due to pairing of bases)


What is DNA?

The hereditary material responsible for passing genetic material from cell to cell and generation to generation


In what ways is DNA adapted to carry out its function?

Very stable - can pass from generation to generation without change

Extremely long - carries an immense amount of information

By having the base pairs within the cylinder of the deoxyribose - phosphate backbone, the genetic information is to some extent protected from being corrupted by outside chemical and physical forces


What is the difference between DNA in eukaryotic and prokaryotic cells?

Prokaryotic - DNA molecules are smaller, form a circle, aren't associated with proteins and don't have chromosomes

Eukaryotic - DNA molecules are larger,more a line, in association with proteins and have chromosomes


What is meant by a degenerate code?

Possibly more than one code of bases for each amino acid


In trying to discover how DNA bases coded for amino acids, scientists suggested that there must be a minimum of 3 bases that coded for each amino acid, what was their reasoning for this?

Only 20 amino acids regularly occur in proteins

Each amino acid must have its own code of bases on the DNA

Only four different bases are present in DNA

If each base coded for a different amino acid only 4 could be coded for

3 bases produce 64 codes which is more than enough to satisfy the requirements of 20 amino acids


What is mitosis needed for?




What happens in meiosis 1 ?

The homologous chromosomes pair Upanishads their chromatids wrap around each other. Equivalent portions of these chromatids may be a
Exchanged by crossing over.

By the end of this stage the homologous pairs have separated, with one chromosome from each pair going into one of the two daughter cells


What happens in meiosis 2 ?

The chromatids move apart and at the end four cells have been formed. In humans each of these cells contain 23 chromatids.


What happens in prophase?

Chromosomes become visible in nucleus

Nuclear membrane breaks up

Centrioles form a fibrous spindle


What happens in metaphase?

Chromosomes attach to spindle by centromere

Line up along equator


What happens in anaphase?

Separation of sister chromatids

Spindle fibres shorten - causes chromatids to be pulled to opposite poles by centromere


What happens in telophase?

Disintegration of spindle

Nuclear membrane reforms

Chromosomes unravel - chromatin


What are the three parts of interphase?

First growth phase - when the proteins from which cell organelles are synthesised are produced

Synthesis phase - when DNA is replicated

Second growth phase - when organelles grow and divide and energy stores are increased


What effect does selective breeding have on genetic diversity?

The variety of alleles in the population is deliberately restricted to s small number of desired alleles. Over many generations, this leads to a population all of which poses the desired qualities but which has reduced genetic diversity


What is the founder effect?

This occurs when just a few individuals from a population colonise a new region. These individuals carry with them just a small fraction of alleles - reduced genetic diversity


How is immunological comparisons of proteins carried out?

Serum albumin from species A injected into species B

Species B produces antibodies specific to all the antigen sites in this albumin

Serum is extracted from species B, this contains the antibodies produced

Serum from B is the on mixed with serum for a third species C

The antibodies respond to their corresponding antigens on the albumin in the serum of C

The response Is the formation of a precipitate

The greater the number of similar antigens the more precipitate and the more closely the species are related