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Topic 1: Biological molecules > DNA > Flashcards

DNA Flashcards

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Organic Chemistry 101 flashcards
1
Q

nucleotide

A

monomer from which nucleic acids are formed

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2
Q

what does each nucleotide comprise ?

A

a pentose, a phosphate group and a purine or pyrimidine base

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3
Q

what are the two types of nucleic acids ?

A

DNA ( deoxyribonucleic acid ) and RNA ( ribonucleic acid )

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4
Q

Structure of nucleotides

A

each nucleotide consists of three substances combined together:
- a pentose
- nitrogenous base
- phosphoric acid

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5
Q

nitrogenous base

A
  • a double ringed purine (either adenine or guanine) - in both DNA and RNA
  • a single ringed pyrimidine (either cytosine or thymine) - DNA
    (either cytosine or uracil)
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6
Q

polynucleotide chains

A

two nucleotides can be joined together by a condensation reaction catalysed by an enzyme DNA polymerase
- formation of a covalent bond, called a phosphodiester bond

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7
Q

how does DNA polymer occur in pairs ?

A

joined by hydrogen bonds between bases - creates a double helix

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8
Q

nucleotide + nucleotide =

A

dinucleotide

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9
Q

how do polynucleotides form ?

A

large numbers of nucleotides become condensed together to form huge molecules

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10
Q

how do backbone of the polynucleotide form ?

A

alternating sugar and phosphate molecules

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11
Q

where can hydrogen bonds only form ?

A

between complementary base pairs
- cytosine and guanine
- adenine and thymine

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12
Q

what is RNA ?

A

a polymer of a nucleotide formed ribose, a nitrogenous base and a phosphate group

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13
Q

what are the nitrogenous bases in RNA ?

A

adenine, guanine, cytosine and uracil

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14
Q

Pyrimidines

A

single stranded structure
- cytosine and thymine

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15
Q

purines

A

double ringed structure
- guanine and adenine

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16
Q

what are the three types of RNA ?

A

messenger RNA
transfer RNA
ribosomal RNA

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17
Q

messenger RNA

A

carries a copy of a single gene to a cells ribosomes

18
Q

transfer RNA

A

carries individual amino acids to ribosomes during protein synthesis

19
Q

ribosomal RNA

A

forms part of the sub units of ribosomes

20
Q

what does DNA only use ?

A

A, T , C and G

21
Q

bonding - RNA molecules

A
  • base + sugar joins with a glycosidic bond
  • the phosphate + sugar joins an ester bond
  • both require condensation reaction to occur
22
Q

in every DNA nucleotide:

A
  • pentose is deoxyribose
  • the base is cytosine, guanine, adenine, or thymine, but never uracil
23
Q

complementary base pairing

A

leads to:
- stability of the DNA double helix
- transfer of genetic information from DNA to RNA
- the way amino acids are assembled into polypeptides in the cytoplasm

24
Q

A joins with what

A

T

25
Q

C joins with what

A

G

26
Q

the bases of two strands fit together only if:

A

the deoxyribose molecules to which they are attached point in opposite directions

27
Q

which directions do the sugar phosphate backbones ?

A

opposite directions - strands are antiparallel

28
Q

Semi conservative replication - step 1

A

the double helix of the DNA molecule unwinds and the hydrogen bonds holding the strands together break - causes the bases on each strand to become exposed

catalysed by the enzyme DNA helicase

29
Q

Semi conservative replication - step 2

A
  • both exposed strands now acts as a template for the production of the new polynucleotide strand
  • free nucleotides are attached to the exposed complementary bases
    -DNA polymerase links the adjacent nucleotides forming phosphodiester bonds - the sugar phosphate backbone
30
Q

Semi conservative replication - step 3

A
  • DNA is replicated in segments
  • DNA ligase joins the segments together - condensation reaction - forms phosphodiester bonds
31
Q

Semi conservative replication - step 4

A

two identical DNA molecules are formed
- semi conservative replication because each strand contains 1 copy of the original DNA

32
Q

Genetic code

A

major role: enable a cell to make specific proteins
- large DNA molecule codes for a large number of proteins

33
Q

gene

A

a sequence of bases which code for specific amino acids in a polypeptide chain

34
Q

what is a genetic code ?

A

a combination of three nucleotide base triplets encodes an individual amino acid
- each combination of base triplets encodes the same amino acid in all organisms

35
Q

what is universal ?

A

triple code

36
Q

With four bases, how many different combinations can be made ?

A

64 (4x4x4)

37
Q

how many amino acids are commonly used by cells ?

A

20
- there is many more different and DNA base triplet combinations than are needed to encode 20 amino acids

38
Q

degenerate

A

some amino acids are encoded by more than one base triplet

39
Q

genetic code

A
  1. it has one 3 base start codon = TAC
  2. it has 3 different 3 base stop codons = ATT, ATC and ACT
  3. 3 bases code for a specific amino acid
40
Q

why is the genetic code non overlapping ?

A

each triplet only read once and triplets don’t share any bases

Topic 1: Biological molecules (11 decks)

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