DNA Flashcards
The discovery of DNA
- Rosalind Franklin took the first clear X-ray diffraction image of DNA in 1952
- confirmed the spiral nature of DNA
Eukaryotic cells
DNA bound to proteins in chromosomes in nucleus enclosed in nuclear membrane
Also found in mitochondria and chloroplasts
Prokaryotic cells
Unbound circular DNA in nucleoid membrane - not bound by a nuclear membrane
DNA - deoxyribonucleic acid
smaller repeating subunits of nucleotides
double stranded
rungs of ‘ladder’ are bases
- held by weak hydrogen bonds
Nucleotide consists of
- phosphate group
- deoxyribose sugar / ribose sugar
- nitrogenous base
4 bases for DNA
complementary base pairs
- cytosine and guanine
- adenine and thymine
Nucleotides
building blocks of DNA
held together by:
strong chemical bonds - phosphodiester bonds
- between sugar and phosphate units
RNA - ribonucleic acid
uracil replaces thymine
one stranded
the purpose of DNA replication
- duplicate the code it carries - passed to daughter cells
DNA replication - eukaryotic cells
chromosomes gain a sister chromatid - x2 stranded
when does DNA replication occur?
S phase of interphase of the cell cycle
The process of DNA replication
1.
DNA helicase (enzyme) unwinds/separates the double strand by breaking the weak H bonds
The process of DNA replication
2.
Enzyme primase attaches a short sequence of RNA - primer - to show DNA polymerase - to start adding nucleotides
The process of DNA replication
3.
Complementary nucleotides added by enzyme DNA polymerase. Synthesis of ne daughter is in a 5’ to 3’ direction
A & T C & G
The process of DNA replication
4.
Result is the production of two identical DNA molecules - each made of one parent strand & one daughter strand
- semi conservative
synthesis along continuous & discontinuous strands
- synthesis is continuous along the leading strand
- synthesis is discontinuous along the lagging strand
- primers are attached at short intervals, starting from the replication fork
- DNA polymerase synthesises short strands of new DNA called okazaki fragments
- DNA polymerase moves in opposite direction on two anti-parallel parent strands
