nucleic acids and protein synthesis Flashcards
what is DNA
- deoxyribonucleic acid
- chemical substance that is present in the nucleus
- controls all the chemical changes which take place in the cell
- the kind of cell which is formed is controlled by the DNA
what makes up DNA
- a long strand of subunits called nucleotides
- each nucleotide is made up from a deoxyribose sugar and a phosphate group and an organic base
what are pyrimidines
- they are single ringed bases
- cytosine
- thymine
- uracil
what are purines
- double ring bases
- adenine
- guanine
what is the complimentary base pairing rule
- the bases always pair up in the same way
- adenine bonds with thymine or uracil with hydrogen bonds
- guanine bonds with cytosine using hydrogen bonds
what is the replication process
- described as semi-conservative replication
- the strands unwind and separate
- each strand becomes a template for the new strands
- the nucleus of the cells will contain identical DNA because of complimentary base pairings
what are the stages of DNA replication
- the enzyme DNA helicase separates the two strands
- each separated strand is now a template
- free DNA nucleotides bind to the template suing complimentary base pairing
- this is done using DNA polymerase
- this creates DNA which is identical to the original strand
what is the evidence of semi conservative replication
- messelson and stahls experiment
- they grow the first generation in heavy nitrogen
- they then grew the second generation in light nitrogen and it was mixed density
- the third generation had some light and some mixed DNA
what is RNA
- single stranded polymer
- contains ribose sugars
- bases = adenine, guanine, cytosine, uracil
- three types
what is the structure and function of the mRNA
structure:
- long, single stranded, forms a helix
function:
- manufactured in the nucleus
- carries genetic code from the DNA to the ribosome
what is the structure and function of rRNA
structure:
- long, large, complex
- made up of double and single helices
function:
- makes up ribosomes
what is the structure and function of tRNA
structure:
- small, single stranded
- clover leaf shape
- one end contains anti codon
- the other end brings the amino acid
function:
- bring amino acids to the ribosome so that proteins can be synthesised
explain genetic code
- its a sequence of bases in the DNA
- a group of three bases, also called a triplet, controls production of a particular amino acid
- the order of amino acids determines what protein its going to be
what is a triplet code
- three bases in DNA sequence code for an amino acid
explain genes
- a triplet code forms a gene
- there may be thousands of bases for one gene
- length of DNA that codes for a polypeptide
- each gene occupies a specific place on the chromosome
what is the one gene one polypeptide hypothesis
- one gene will code for a polypeptide
what are the characteristics of the genetic code
- it is a triplet code or codon
- it is a degenerate code meaning an amino acid can have more than one codon
- some indicate stop
- all the codons are universal
- the code is non overlapping and will be read separately
