hydrogen bonds
the nucleotides in each polynucleotide strand have base pairs which are held together by covalent bonds and the two polynucleotides are held together by hydrogen bonds. These hydrogen bonds are important as they hold two polynucleotides together to stabilize double stranded DNA but are weak enough to be broken when need for replication---------------------------------------------------------------------------------
base paring
base paring is important because there is complementary base paring in DNA which ensures that the code carried on the DNA strands can be copied and it allows DNA to pass on the code to make proteins---------------------------------------------------------------------------------
Semi-conservative replication
this is semi-conservative because new DNA molecule is made of one old strand and one new strand. This replication occurs in interphase before mitosis
process of semi conservative replication
- DNA unwinds. hydrogen bonds breaks as enzyme helicase separates the two polynucleotides
- free nucleotides assemble against both strands
- DNA polymerase catalyses attachment of nucleotide to new strand. DNA nucleotide travels along template in the 3' to 5'. new strand is assembled in 5' to 3' so one strand is continuous while one is lagging
- DNA polymerase checks sequence of DNA and DNA ligase joins Okazaki fragments
- hydrogen bonds from between polynucleotide strands and winding enzyme winds up the DNA molecule forming two new strands
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Transcription - production of an mRNA molecule with a complementary base sequence to one strand of a length of DNA
Process of transcription
- DNA unwinds in specific areas and DNA helicase breaks the hydrogen bonds
- free nucleotides slot into place and there is base pairing and nucleotides from phosphodiester bonds which is catalysed by RNA polymerase
- the elongation of the mRNA molecules continue until the end of the gene is reached which is signaled by a particular codon
- mRNA molecule is then guided out of the nucleus through the nuclear pore and passes into the cytoplasm
Translation - process by which code for making the protein is used to line up amino acids in a particular sequence and link them together to make a polypeptide
Process of translation
- mRNA molecule is held in a cleft in the ribosome
- a tRNA which an anticodon that is complementary to the first mRNA condon binds with it (initiation)
- another tRNA binds with the next codon and a condensation reaction occurs binding the two amino acids together
- mRNA moves along the cleft of the ribosome and a third tRNA binds with codon and a third amino acid is added to the chain while the first tRNA break away
- Process continues until polypeptide chain gradually built up until stop codon is reached (termination)
