1.1 structure & replication of DNA Flashcards
describe the structure of DNA
double stranded, double helix with anti-parallel strands
describe how hydrogen bonds are involved with the structure of DNA
complementary base pairings are held together by weak hydrogen bonds.
describe the structure of a nucleotide
nucleotides consists of deoxyribose sugar, phosphate and base, sugar–phosphate backbone, base pairing (adenine–thymine, guanine–cytosine) held together by weak hydrogen bonds.
with reference to 3’ end and 5’ ends, describe the antiparallel arrangement of DNA
the two DNA strands in the double helix are anti-parallel, there is a deoxyribose sugar at the 3’end and phosphate group at 5’end
describe complementary base pairing in DNA
Adenine pairs with thymine, cytosine pairs with guanine, complementary base pairings are held together by weak hydrogen bonds
state the link between DNA base sequences in relation to an organism
base sequence of DNA forms the genetic code of an organism
state the organisation of DNA in prokaryotes
prokaryotes contain single circular chromosomes and also contain smaller circular plasmids. Do not have a membrane bound nucleus.
describe the organisation of DNA in eukaryotes
eukaryote contain linear chromosomes, consisting of tightly coiled DNA wrapped around associated proteins (histones). Found within a membrane bound nucleus. some organelles (chloroplasts/mitochondria) contain DNA in small, circular chromosomes.
organisation of eukaryote yeast
has DNA in the form of plasmids in addition to linear chromosomes
describe the roles of dna polymerase and primers
- DNA polymerase creates new dna strands by joining nucleotides together.
- Primer is a short strand of nucleotides that serves as a starting point for enzyme dna polymerase to add nucleotides at the 3’ end of the template dna strand.
describe the replication in the leading strand in DNA replication
1- the DNA double helix is unwound and hydrogen bonds between complementary bases are broken to form two template DNA strands.
2- primer binds to 3’ end of 3-5’end leading strand in order to start replication.
3- enzyme DNA polymerase can only add DNA nucleotides in one direction, resulting in leading strand being replicated continuously.
4- DNA polymerase adds DNA nucleotides using complementary base pairings.
5- on lagging strand primers are added one by one.
6- DNA is added to the lagging strand in the form of fragments.
7- the fragments are then joined together to form a complementary strand by enzyme DNA ligase.
state the purpose of PCR and how this is achieved
pcr amplifies dna by using complementary primers for specific target sequences. primers are complementary to specific target sequences at the two ends of the reigon of dna to be amplified. reapeated cycles of cooling and heating amplify target reigon of dna.
pcr stages
92-98 dna strands are seperated as hydrogen bonds between complementary bases are broken due to high temperature.
50-65 cooling allows primers to bind to specific target dna sequences.
70-80 heat tolerant dna polymerase repliactes dna reigon to be copied.
role of primers in pcr
to bind to specific target dna sequences to be copied and to allow a starting point for heat tolerant polymerase to replicate dna sequence.
two primers are required as there are two strands in indentified dna sequence and each requires a complementary primer at its 3’ end.
in stage 3 why is heat tolerant polymerase used
unlike normal DNA polymerase, DNA polymerase is not denatured by high temperatures used in PCR.
