Nucleic Acids Flashcards
Draw and describe DNA (include bases and structure)
There should be one phosphate group, one pentose sugar (deoxyribose), one nitrogenous base (adenine, thymine, guanine, cytosine, uracil for RNA)
A condensation reaction between the phosphate group on one and the sugar of another, forming the phosphodiester bond. Molecule is twisted into a double helix where strands are anti parallel to each other. Has 2 sugar phosphate backbones attached by complementary bases.
What are the bases grouped into?
Purines: adenine and guanine
Pyrimidines: thymine and cytosine and uracil
What is gene?
A sequence of DNA nucelotides that codes for a polypeptide. Each amino acid is coded for by a sequence of 3 bases in a gene. The order of bases determine the order of amino acids. The large molecule is tightly wound around histone proteins into a chromosome
What is the importance of hydrogen bonds?
GC has 3 H bonds
AT has 2 H bonds
The bonds give equal sized rungs on the DNA ladder that can twist around an axis into the double helix = stability
H bonds = unzip for transcription
Briefly describe the extraction and purification of DNA
Strawberries, kiwis etc
- macerating material
- adding strong detergent
- add ethanol so DNA precipitates out of solution
- can be purified further
Describe how semi conservative replication occurs
- unwinds gyrase
- unzips DNA helicase hydrogen bonds broken
- free phosphorylated nucleotides in nucleoplasm are bonded to exposed bases by complementary base pairing
- DNA polymerase catalyses the addition of new nucleotide baes in the 5’ 3’ direction (single strand is template)
- leading strand is synthesised continuously lagging strand is discontinuous, later joined by ligase
- hydrolysis of activated nucleotides to release extra phosphate groups suplies energy to make phosphodiester bonds
Give some information about mutations
Errors may occur, 1 in 10^8 base pairs, this could change genetic code, there are enzymes that proof read and edit out nucleotides. Some mutations are good, bad or neutral.
Mistakes lead to mutations, mutations lead to development of proteins with different shapes = ineffective and lead to tumours
A frameshift in genetic code causes a change in the amino acid sequence = non functional protein
What makes RNA different from DNA?
- ribose
- uracil
- single stranded
- shorter
What are the 3 forms of RNA and what do they do?
mRNA = complementary to template, it's a copy of DNA coding strand) rRNA = component of ribosomes tRNA = carries amino acids to the ribosomes (bonded to form polypeptide)
Explain the nature of the genetic code
- universal - all living things have same triplet of bases codes for same amino acids
- degenerate - more than one base triplet for amino acids, reduce effect of point mutations
- non overlapping - read from a fixed point
Describe how transcription occurs
- unwinds and unzips
- hydrogen bonds between complementary nucleotides break exposing them
- RNA polymerase formation of temporary hydrogen bonds between RNA nucleotides and their complementary unpaired DNA bases (on the template strand)
- RNA is complementary to the template strand, it is a copy of DNA coding strand
- mRNA passes out of the nucleous through nuclear envelope and attaches to the ribosome
Describe how translation occurs
- [mRNA moves to ribosome] tRNA brings specific amino acids and find their place when the anticodon binds by temporary hydrogen bonds to codon on mRNA [1] [1]
- as ribosome moves along length of mRNA it reads the code and when 2 amino acids are next to each other a peptide bond froms [1]
- ATP is needed
- after assembly the mRNA breaks down, recycled
- newly synthesised polypeptide is helped by chaperone proteins to fold into 3D shape
What triplets are there?
- triplet bases on DNA = base triplet
- triplet of bases on mRNA = codon
- triplet of bases on tRNA = anticodon
What evidence is there for semi conservative replication?
Conservative = original molecule acts as template and new molecule made
Dispersive = orginal breaks up and new ones join up
Semi conservative = new molecule consists on one original strand and one newly formed strand
- grew bacteria 14 generations in N-15
- transfer some bacteria into medium N-14 to undergo one replication
- hybrid, showed it wasn’t conservative = one light and one dark
- divide again = one hybrid and one light showed not dispersive
Explain how bonds are formed between RNA nucleotides
[1] hydrogen atom is removed from OH group on carbon 3 of ribose sugar of one nucleotide
[1] OH is removed from phosphate group of other nucleotide
[1] covalent bond formed between caron 3 of ribose and phosphate group
