DNA and Meiosis

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what are individual nucleotides made up of?
a sugar (deoxyribose), a phosphate groups, and an organic base
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what are the organic single-ring bases?
cytosine and thymine
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what are the organic double ring bases?
adenine and guanine
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how is the deoxyribose sugar, phosphate groups and organic base combined and what does this form?
condensation reaction, a single nucleotide
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what do two mononucleotides bond to form?
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what does the continued linking of mono nucleotides form?
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what is DNA made up of?
two long strands of nucleotides (polynucleotides), joined together by hydrogen bonds formed between bases
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what do the organic bases contain?
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what is the difference between the bases with a double ring structure and those with a single ring structure?
the double-ring strutted bases have longer molecule if the rungs of DNA are to be the same length the bases have to join through one of each type of ring
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how many bonds is between adenine and thymine?
two hydrogen bonds
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how many bonds is between cytosine and guanine?
three hydrogen bonds
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what is the word used to describe the base pairing?
that the bases are complementary to each other i.e. adenine is complementary to thymine
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what varies in the bases?
the ratio of adenine and thyme to guanine and cytosine in different species
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what is the shape of DNA?
A double helix formed by phosphate and deoxyribose being wound one another forming a structural backbone of DNA molecules.
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how many base pairs are in a complete turn of this helix?
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What is DNA?
a hereditary material responsible for passing genetic information from cell to cell and through different generations
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how many base pairs are there in the DNA of a typical mammalian cell?
3.2 million.
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what does this number mean?
there is an infinite variety of sequences of bases along the length of a DNA molecule. therefore, this variety provides immense genetic diversity
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how is a DNA molecule adapted to carry out its functions?
it is stable and can pass through generations without change, its two separate stands are joined with hydrogen bonds allowing separation during DNA replication, its an extremely large molecule so carries a vast amount of genetic information
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how id the genetic information protected from being corrupted by outside chemicals and physical forces?
by having the base pairs within the helical cylinder of the deoxyribose-phosphate backbone.
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why did scientists focus their attention on chromosomes as a site of hereditary material?
chromosomes are made up of proteins and DNA, to produce exccesive variety of cells and organism that exists the hereditary material must be diverse so each organism could have its own specific type
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why would proteins be more of a likely candidate of the hereditary molecule?
they have considerable chemical diversity and proteins such as enzymes and antibodies show great specificity
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what is a gene?
sections of DNA that contain the coded information for making polypeptides?
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how the the coded information produced?
in the form of a specific sequence of bases along the DNA molecule
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why do genets determine the proteins of an organism?
polypeptides combine to make proteins
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why do genes determine the nature and development of all organisms?
enzymes control chemical reactions and are responsible for an organisms development and activities
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how does genes link to proteins?
a gene is a sequence of DNA bases that determines a polypeptide and a polypeptide is a sequence of amino acids
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what is DNA coded for and what is it made up of?
it is CODED for amino acids, and its MADE UP OF nucleotides
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what is the triplet code?
that there is a minimum of three bases that coded for each amino acid?
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why did scientists come up with the triplet code?
there are 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, if each base codes for a different amino acid four amino acids could be coded for
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what is the adequate number of bases produced and how did scientists work this out?
64 (4^3), vecuase using a pair of bases 16(4^2) different codes are possible= inadequate. three bases produces 64 (4^3) different codes more than enough to satisfy the requirements of 20 amino acids
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why would some amino acids have more than one code?
as there are 64 possible codes and only 20 amino acids
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why does the nuclear DNA in eukaryotes not code for amino acids?
because these sections are called introns and can occur within genes and as multiple repeats between genes
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describe some features of the triplet code:
a few amino acids have only a single triplet code, the remaining have between two + 6 triplet codes, the code is knows as a degenerate code because most amino acids have more than one triplet code
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how is the triplet code read?
in one particular direction along the DNA strand.
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what is the start of a sequence =?
always the same triplet codes, this codes for the amino acid methionine. if it does not form part of the final polypeptide it is later removed
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what are stop codes?
when three triplet codes do not code for any amino acid and mark the end of a polypetide chain
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why is each base in the sequence read only one?
because the code is non overlapping
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why is the triplet code the same in all organisms?
because it is universal
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what is the DNA like in prokaryotic cells?
in prokaryotic cells, the DNA molecules are smaller and form a circle and are not associated with protein molecules, and they do not have chromosomes
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what is the DNA like in Eukaryotic cells?
larger, form a line rather than a circle and occur in association with preteens to form chromosomes
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describe the structure of a chromosome
two threads joined to a single point, each threat is called a chromatid and the centre is called the centromere
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when are chromosomes visible as distinct structures?
when a cell is dividing
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how is DNA compact to form chromosomes?
the DNA is wound around proteins to fix it in position, the DNA-protein complex is then coiled. the coil is looped and further coiled and then packed together to form achoromosomes
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what do chromosomes contain?
a single molecule of DNA, with many genes each occupying a specific position along the DNA molecule.
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does the number of chromosomes vary? how many chromosomes are in a human
YES! 46
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why in almost all species is there an even number of chromosomes in the cell of adults?
because chromosomes occur in pairs called homologous pairs
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why do chromosomes occur in pairs?
sexually reproduction and the fusions of games contribute to a set of chromosomes in the offspring therefore one of each pair is derived from the chromosome provided by the mother in the egg.
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what are the pairs known as ?
Homologous pairs?
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what is the total number of chromosomes referred to as ?
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define homologous pairs?
always two chromosomes that determine the same characteristic, but is not identical
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define diploid?
a tern applied to cells in which the nucleus contains two seta of chromosomes.
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why are homology pairs not identical?
because they may posses information on eye colour but the one chromosome may carry the codes (allele) for blue eyes while the oner for brown
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how is it ensured that each daughter cell receives one chromosome from each homologous pair?
during meiosis the halving of the number of chromosomes is done in a certain manner, when these haploid cells combine the diploid state with paired homologous chromosomes is restored
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define haploid?
a term applied to cells that only contain a single copy of each chromosome
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define allele?
one of a number of alternative forms of a gene
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how are alleles passed on and what happens when they are different?
inheriting one allele from each of its parents. when they are different each allele will code for a different polypeptide.
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what will differences in the base sequence of an allele of a single gene result in?
a different sequence of amino acids being coded for which will lead to the production of a different polypeptide and therefore the production of a different protein.
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what can the consequence be of a difference in the base sequence of an allele?
the different protein may not function properly or at all, if it is an enzyme it may have a different shape and therefore an enzyme-substrate complex may not form so as a result the enzyme may not function, this can have serious consequences
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define mitosis
the production of two daughter nuclei with the same number of chromosomes as the parent cell and as ash other
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define meiosis:
the production of four daughter nuclei each with half the number of chromosomes as the parent cell
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what would happen without meiosis?
because during sexual reproduction if each gamete had a full set of chromosomes then the cell that they produced would have double this number. this doubling would continue till the next generation
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why is meiosis necessary?
to maintain a constant number of chromosomes in the adults of species, so the number of chromosomes must be halved at some stage of the life cycle.
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what happens during meiosis?
the chromosome pairs separate so that only one chromosomes from each pair enters each gamete which is known as the haploid number of chromosomes.
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what does meiosis involve?
two nuclear divisions that occur one after the other
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what are the two nuclear diversions?
meiosis 1, and meiosis two
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what happens in the first division?
homologous chromosomes pair up and their chromatids warp around each other, some equivalent portions of these chromatids may be exchanged during crossing over, by the end of the stage the homologous pairs have separated into two daughter cells
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what happens in the second meiotic division?
the chromatids move apart at the end of meiosis 2 and four cells have been formed each containing 23 chromatids
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what does meiosis do?
half the number of chromosomes, and produce genetic variation among offspring allowing an organism to adapt and survive in a changing world
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how does meiosis bring about genetic variation?
independent segregation of homologous chromosomes, recombination of homologous chromosomes by crossing over
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define gene:
a section of DNA that codes for a polypeptide
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define locus?
a position of a gene on a chromosome of DNA molecule
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what happens during independent secretions of homologous chromosomes?
during meiosis 1 each chromosome lines up alongside its homologous partner, they do this randomly, one pair will pass to each daughter cell, and which one of the pair goes into the daughter cell and with any other pairs depends how the pair lined up
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why is it called in dependent segregation?
the pairs are lined up at random, the combination of the chromosomes that goes into the daughter cell at meiodid is also random.
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how can variety form new genetic combinations?
alleles of the genes may differ and the random distribution and consequence of independent assortment of those chromosomes produces new genetic combinations
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what stays the same?
each member of a homologous pair of chromosomes have exactly the same gene and therefore determines the same characteristics
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why will the gametes in meiosis be genetically different?
as a result of different combinations of maternal and paternal chromosomes they contain. the haploid gametes fuse together randomly at fertilisation, each gamete has a different make up and their random fusion together produces variety
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describe genetic recombination by crossing over:
the chromatids of each pair become twisted around one another, during this tensions are created and poisons of the chromatids break off these rejoin with chromatids of its homologous partner, usually the equivalent portions of homologous chromosomes
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why is the process known as crossing over?
becquse chromatids cross over one another many times
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why is the process called recombination?
the broken-off portions of chromatid recombine with another chromatid
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what happens if there is no recombination?
only two different types of cells are produced
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what happens when there is recombination?
four different types are produced therefore increasing genetic diversity
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Other cards in this set

Card 2


what are the organic single-ring bases?


cytosine and thymine

Card 3


what are the organic double ring bases?


Preview of the front of card 3

Card 4


how is the deoxyribose sugar, phosphate groups and organic base combined and what does this form?


Preview of the front of card 4

Card 5


what do two mononucleotides bond to form?


Preview of the front of card 5
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