2.1 - structure of RNA and DNA Flashcards
what 3 components are individual nucleotides made out of
- a pentose sugar
- a phosphate group
- a nitrogen containing organic base. (these are: cytosine (C), thymine (T), uracil (U), adenine (A) and guanine (G)
how are the pentose sugar, phosphate group, and organic bases joined in a nucleotide structure
- condensation reactions to form a single nucleotide (mononucleotide)
how many mononucleotides are joined as a result of a condensation reaction between between the deoxyribose sugar of one nucleotide and the phosphate group of another
2
what is the bond between between nucleotides called
phosphodiester bond
what do you call 2 mononuleotides joined together
dinucleotide
–> more than 2 is called a polynucleotide
what is Ribonucleic acid
polymer - made up of nucleotides
describe the structure of Ribonucleic acid
- single, relatively short polynucleotide chain in which:
1. pentose sugar = ribose
2. the organic bases = A,G,C,U - 1 type of RNA: transfers genetic info from DNA –> ribosomes
- The ribosomes themselves: made out of proteins and another type of RNA
- 3rd type of RNA: involved in protein synthesis
who worked out the structure of DNA
- 1953: James Watson and Francis Crick
- following previous pioneering work on the X-ray diffraction patterns of DNA
describe the structure of DNA
- the pentose sugar = deoxyribose
- the organic bases =A,T,G,C
- made of 2 strands of polynucleotides
- each strand = long + joined together by hydrogen bonds between certain bases
describe what is meant when we say that DNA can be thought as a ladder
- a ladder, where the phosphate and deoxyribose molecules alternate to form the uprights
- and the organic base pair together to form the rungs
- the 2 strands are twisted around, so that the uprights of Phosphate and deoxyribose wind around each other, forming a double helix
- this forms the structural backbone of the DNA molecule
how do the bases on the two strands of DNA attach together?
hydrogen bonds, its these bonds that hold the 2 strands together
is base pairing specific
- yes
- adenine ALWAYS PAIRS WITH thymine
- Guanine ALWAYS PAIRS WITH cytosine
- therefore they’re complementary to each other
describe the quantities of A,T,G,C in DNA
- A same quantity as T
- G same quantity as C
- However ratio of A and T, to G and C = varies from species to species
why is DNA a stable molecule
- The phosphodiester backbone protects the more chemically reactive organic base inside the double helix
- Hydrogen bonds link the organic base pairs forming bridges (rings) between the phosphodiester uprights. Because there’s 3 hydrogen bonds between C and G, the higher the proportion of C–G pairings, the more stable the DNA molecule
what is the function of DNA
- DNA is the hereditary material responsible for passing genetic information from cell to cell and generation to generation
what are some the ways that DNA molecules are adapted to carry out their function
- very stable structure which normally passes from generation to generation without change. Only rarely does it mutate
- 2 separate strands are joined only with hydrogen bonds = allows them to separate during DNA replication and protein synthesis
- It is an extremely large molecule = carries an immense amount of genetic information
- by having the base pairs within the helical cylinder of the deoxyribose-phosphate backbone = genetic info is protected from being corrupt by outside chemical/physical forces
- base pairing = DNA being able to replicate and to transfer info as mRNA
what does the function of DNA rely on
the sequence of base pairs that it possesses
Asses the advantages of scientists questioning the validity of a current theory rather than automatically accepting it
- alternative theories can be explored and investigated
- therefore: new facts may emerge and so a new theory is put forward or the existing one is modified
- In this way, scientific progress can be made
how do scientists use observations, hypothesis’, predictions and investigations
- Scientists work by using observations and current knowledge to form a hypothesis
- from this, they make predictions about the investigation
- by doing the investigation a number of times = collect evidence = accept or reject hypothesis
explain what is meant by the term ‘hypothesis’ in the scientific sense
A suggested explanation of something based on some logical scientific reasoning or idea
how are carbon atoms in the pentose molecule numbered
- 3’ (3-prime) and 5’ (5-prime)
- the 5’ carbon has an attached phosphate group
- the 3’ carbon has a hydroxyl group
how are nucleic acids synthesised and why
- only synthesised ‘in vivo’ in the 5’-to-3’ direction
- because: the enzyme DNA polymerase that assembles nucleotides into a DNA molecule can only attach to the hydroxyl (OH) group on the 3’ carbon molecule
Suggest what the term ‘in vivo’ means in the context of synthesising DNA
- It means ‘in life’
- in other words the synthesis of DNA by a living organism rather than in a lab
From your knowledge of the way enzymes work, explain why DNA polymerase can only attach nucleotides to the hydroxyl (OH) group on the 3’ carbon molecule
- enzymes = specific
- their active site = specific shape that fits their substrate
- shape of the 3’ end of the molecule with its hydroxyl group fits the active site of DNA polymerase
- whereas the shape of the 5’ does not
