Nucleic acids Flashcards
(33 cards)
structure of a nucleotide
nitrogenous base (rectangle), phosphate group (circle), pentose sugar (pentagon)
what elements do nucleotides contain?
carbon, hydrogen, oxygen, nitrogen, phosphorus
pentose sugar in DNA and RNA
DNA - deoxyribose (one less oxygen atom on bottom right carbon)
RNA - ribose
4 bases in DNA
adenine, guanine, cytosine, thymine
which 2 bases in DNA have double ring structure and what is the name for them?
adenine and guanine - purines
which 2 bases are pyramidines?
cytosine and thymine - single ring structure
4 bases in RNA
adenine, guanine, cytosine, uracil
how are polynucleotides bonded?
phosphate group at carbon 5 of pentose sugar forms covalent bond with hydroxyl group of carbon 3 of another nucleotide
- condensation reaction
what is the bond between 2 nucleotides?
phosphodiester bond
structure of DNA
- 2 polynucleotide strands held together by hydrogen bonds between complementary bases on opposite strands
- 2 polynucleotide strands are anti-parallel - run in opposite directions
- sugar-phosphate backbone on outside with bases in the centre
- distance between 2 strands is constant the whole way down
- 2 strands form double helix
how many bonds are formed between guanine and cytosine?
3 hydrogen bonds
how many bonds are formed between thymine and adenine?
2 hydrogen bonds
differences between RNA and DNA
- DNA found in chromosomes in nucleus, RNA found in cytoplasm
- DNA is extremely long, RNA is relatively short
- 2 polynucleotide strands in double helix, RNA has only 1 polynucleotide strand
- RNA contains ribose, DNA contains deoxyribose
Stages of DNA replication
- DNA helicase attaches to DNA molecule causing H bonds between bases to break
- 2 polynucleotides separate
- free nucleotides line up with complementary base on DNA strands
- free nucleotides held in place temporarily by hydrogen bonds between bases
- DNA polymerase moves down molecule and catalyses formation of phosphodiester bonds between activated nucleotides - condensation reaction
difference between normal nucleotide activated nucelotide
activated nucleotide contains 3 phosphate groups, normal nucleotide contains 1
why is it called semi-conservative replication
- one old strand and one new strand
what is a mutation?
insertion - an incorrect base is inserted into the growing polynucleotide strand during replication changing the DNA sequence
deletion - randon base is missed in DNA sequence
- random
differences between DNA in eukaryotes and prokaryotes
- prokaryotes - circular DNA no free ends, relatively short, not bound to histones
- eukaryotes - linear DNA with 2 ends, much longer, tightly wrapped around histones forming chromosomes
transcription
- DNA helicase breaks H bonds between 2 strands of DNA
- complementary free nucleotides form H bonds with bases on exposed nucleotides of one strand
- RNA polymerase moves along template strand and joins RNA nucleotides forming phophodiester bonds
- enzymes move down DNA until they reach the end of the gene
- strand of mRNA formed
- thymine is replaced by uracil
- once mRNA has synthesised, RNA polymerase detaches from DNA and DNA goes back to double helix structure
- mRNA moves out of nucleus through nuclear pore
- prokaryotic cells - mRNA, in eukaryotic cells - pre-mRNA is spliced to get mRNA
genome
all the genes in a cell
how are mRNA nucleotides read?
as a series of triplets - the genetic code
why is the genetic code degenerate?
most amino acids have more than one triplet coding for them
what does it mean by the triplet code is non-overlapping?
no base is read more than once
what does it mean by the genetic code is universal?
same triplets encode the same amino acids in most organisms on earth
