it contains 2 carbon-nitgrogen rings joined together
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what is a pyrimidine base?
it only has one carbon-nitrogen ring
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what are the purine bases?
A and G
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what are the pyrimidine bases?
C and T
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what do nucluotides join together to form?
polynuclotides
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what bond is formed bettween the phosphate group and the sugar?
phosphodiester bond
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what is a chain of sugarss and phosphates known as?
the sugar-phosphate backbone
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what kind of bonds form between each bas (e.g. A and T)?
hydrogen bonds
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what enzyme is used to break the hydrogen bonds between the strands (bases) in self replication?
DNA helicase
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what then happens?
each original strand acts as a template for a new strand.
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what joins to the exposed bases?
free-floating DNA nucleotides join to the exposed bases by complememntry base pairing.
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what enzyme joins the new new strand together?
DNA polymerase
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what does this form?
the sugar phosphate back bone, and hydrogen bonds between the bases of the original and new strand.
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what do the DNA strands then do?
twist to form a double helix
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what is this type of coping called?
semi-conservative replication
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why?
becauase each DNA molecule has half a new strand and half an old strand
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what are the 3 main types of RNA?
mRNA, tRNA, rRNA
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what is the 1st stage of protein synthesis?
transcription
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describe transcription part 1
RNA polymerase attaches to the DNA double-helix at the begining of the gene.
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describe transcription part 2
the hydrogen bonds break, sperating the strands and the DNA molecule uncoils
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describe transcription part 3
one strand is used as a template for mRNA copy, the RNA polymerase lines up free RNA nuclotides along side the template strand.
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describe transcription part 4
complementry base pairing occursmeans that the strand is complementry to the DNA template strand, but T is replaced with U
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describe transcription part 5
once specific bases are joined up they are joined together forming the mRNA molecule
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describe transcription part 6
RNA polymerase moves along the DNA, seprating the strands and assembling the mRNA strand.
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describe transcription part 7
the hydrogen bonds reform between the DNA strands, the strands coil back together, once RNA polymerase has passed by.
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describe transcription part 8
when RNA polymerase reaches a stop codon, it detaches from the DNA. the mRNA moves out of the nucleus through the nuclear pore and attatches to the ribosome in the cytoplasm.
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what is stage 2 of protein synthesis?
translation
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describe translation part 1
mRNA attaches its slef to the ribosome and tRNA molecules carry amino acids to the ribosome.
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describe translation part 2
a tRNA molecule attaches its anticodon to a complementry start codon on the mRNA molecule
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describe translation part 3
a second tRNA molecule attaches to the second complementry codon on the mRNA strand.
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describe translation part 4
rRNA catalyses the formation of a peptide bon between 2 amino acids attached to the tRNA, joining the amino acids together, then the 1st tRNA molecule leaves, levaing behind its amino acid behind.
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describe translation part 5
this procss continues until a stop codon is reached, the polypeptide chain moves away from the ribosome and translation is complete.
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