2.3 NUCLEIC ACIDS Flashcards
What is a nucleic acid?
Nucleic acids are:
- polymers
- individual units
- DNA is an example#
- nucleotides are linked together to form polynucleotides by condensation reactions and broken down by hydrolysis reactions
DNA facts.
DNA:
- composed of 4 nitrogenous bases (adenine, thymine, cytosine, guanine)
- hydrogen bonds hold complimentary base pairs together on adjacent strands
- deoxyribose sugar
- antiparallel double helix structure
- 10 nucleotides per turn of double helix
What are purines and pyrimidines?
Purines- larger bases containing double carbon ring structures, A and G
Pyrimidines- smaller bases containing single carbon ring structures, T, C and U (RNA)
What is cell replication?
Cell replication is the growth of individual cells or overall organism through repair, replacing or reproduction
What is semi-conservative replication?
Semi-conservative replication is replication that results in one old strand and one new strand present in a daughter molecule
Continuous and discontinuous replication.
Continuous and discontinuous replication:
- DNA polymerase can only work in the 3’ to 5’ direction which poses a problem during replication
- one new strand (leading strand) is made as a continuous piece
- the other (lagging strand) is made in small pieces (Okazaki fragments)
Replication errors.
Replication errors happen as:
- cells need to copy their DNA very quickly and with very few errors
- to do so they use a variety of enzymes and proteins which work together to ensure DNA replication is carried out quickly and smoothly.
DNA replication (semi-conservative).
DNA replication:
1. portion of DNA about to undergo replication
2. DNA helicase breaks hydrogen bonds between bases, two strands separate (replication fork)
3. as strands separate, free nucleotides are attracted to their complimentary base
4. when free nucleotides are lined up DNA polymerase joins them together (phosphodiester bonds)
5. all nucleotides are joined to form a complete polynucleotide chain. two identical molecules of DNA are forms
What is a codon?
A codon is a triplet of three bases that codes for an amino acid
What is the genetic code and what are its features?
The genetic code is the set of rules used by living cells to translate information encoded within genetic material into proteins
- universal
- degenerate
- non-overlapping
Messenger RNA (mRNA).
mRNA:
- single stranded
- straight chained
- messenger of DNA
- U instead of T
Transfer RNA (tRNA).
tRNA:
- single stranded
- clover shaped
- transfer amino acids to ribosome
- contains anticodon which is complimentary to mRNA
Ribosomal RNA (rRNA)
rRNA:
- ribsomal subunits composed of almost equal proportions of rRNA and proteins
- rRNA is important in maintaining the structural stability of protein synthesis and plays a biochemical role in catalysing the reaction
Protein synthesis.
Protein synthesis:
1. DNA is too big to leave nucleus
2. DNA unzipped by helicase
3. free RNA nucleotides base pair to exposed bases of template DNA
4. RNA polymerase forms phosphodiester bonds in soon to be mRNA
5. mRNA leaves nucleus via nuclear pores
6. mRNA arrives at ribosome
7. tRNA arrives at ribosome and complimentary base pairs with mRNA codon
8. as the tRNA and mRNA complimentary base pair, amino acids line up, forming the primary structure of the protein when a peptide bond forms between them (peptidyltransferase)
9. a polypeptide is formed
What do cells require energy for?
Cells require energy for:
- synthesis
- transport
- movement
Making and breaking ATP.
ATP is broken down via hydrolysis (adding water) to form ADP + Pi. ATP is built back up via phosphorylation/condensation reaction (releasing water)
ATP - ADP + Pi (releases energy)
How is energy released through ATP?
How energy is released through ATP:
- energy is needed to break bonds and is released when bonds are formed
- a small amount of energy is needed to break the relatively weak bonds holding the last phosphate group in ATP
- however, a large amount of energy is released when the released phosphate undergoes other reactions involving bond formation
- overall, a lot more energy is released than used
What are the properties of ATP?
The properties of ATP are:
1. not a long-term energy store- due to instability of phosphate group
2. immediate energy store/easily regenerated- due to instability it is rapidly reformed in living cells, so cells do not need a large store of ATP
3. small structure- allows ATP to move more easily in and out of cells
4. water soluble- energy requiring processes happen in aqueous environments
5. releases energy in small quantities- suitable to most cellular needs so that energy is not wasted as heat
