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