DNA structure and function Flashcards
what elements does DNA contain?
carbon, hydrogen, oxygen, nitrogen and phosphorus
what is DNA?
a polymer made from many monomers called nucleotides that are chemically joined together with a phosphodiester bond
what do many nucleotides join together to make? how do these form?
a polynucleotide (DNA is made from two polynucleotide strands)
a condensation reaction joins nucleotides together
what are the three components of a nucleotide?
a pentose sugar called deoxyribose (a sugar with 5 carbons), phosphate group and a base
what element is in a DNA base? what are the 4 bases?
nitrogen
adenine, thymine, guanine and cytosine
what is the phosphate of one nucleotide attached to on another nucleotide?
the deoxyribose of the next nucleotide so there are alternate phosphate then sugar all down the backbone of the strand
this structure is called the sugar-phosphate backbone
what kind of bonds are the phosphodiester bonds in the polynucleotide strand?
strong covalent
how do the two polynucleotide strands in DNA run?
anti-parallel to each other
one runs in the 5’ to 3’ direction whilst the other runs 3’ to 5’
where is the 3’ end of a polynucleotide strand?
the hydroxyl group that is attached to the deoxyribose sugar of the strand
where is the 5’ end of the polynucleotide strand?
the phosphate group
what are the two polynucleotide strands in DNA held together by?
hydrogen bonds between complementary bases
explain what is meant by ‘complementary base pairing’?
each base can only pair with a certain other base- adenine with thymine and cytosine with guanine
how many hydrogen bonds are between A and T and C and G? how can we remember this?
adenine and thymine = 2
cytosine and guanine =3
tea for two!
what do the two anti-parallel strands do?
twist to make the DNA double helix
what are the functions of DNA?
-holds genetic info
-holds the genetic code for
production of proteins
-can replicate to produce DNA for new cells and cell division
what is the benefit of DNA being large/long and being coiled around histones?
makes it compact and enables a large amount of genetic info to be stored in a cell
what does the base sequence of DNA form?
the genetic code for making proteins with triplets of bases coding for one amino acid
the base sequence of DNA determines where…
tRNA molecules carrying specific amino acids complementary base pair
and therefore determines the sequence of amino acids that forms the primary structure of proteins
why is it important that the phosphodiester bonds strong?
so that the sugar-phosphate backbone gives strength and stability to the molecule
what is meant by ‘strong phosphodiester bonds maintain the integrity of the code’?
nucleotides cannot easily break away and re-join in a different sequence
what is the strength of the hydrogen bonds holding the polynucleotide strands together?
weak so easily broken
why is it a benefit that hydrogen bonds are weak?
so strands can be separated and act as template strands for DNA replication and for transcription/ production of mRNA for protein synthesis.
why is complementary base pairing important for DNA function?
enables DNA to be identically replicated
what is the benefit of the MANY hydrogen bonds between polynucleotide strands?
gives strength and stability to the DNA molecule.
