Nucleicacid Dna Flashcards
Replication
DNA synthesis by copying of existing DNA
Transcription
RNA synthesis by copying of DNA
RNA processing
Modification of RNA in the nucleus
Translation
Protein synthesis by decoding of RNA
Nucleic acid are composed of what
Monomeric units made up of an ‘information coding’ nitrogen base (purines and pyrimidines)
Adenine, Guanine
Thymine, Cytosine, Uracil
A sugar scaffold to hold the bases
Ribose in RNA
Deoxyribose in DNA
A phosphate connector
five principal bases in nucleic acids
A, G, T, C are present in DNA
A, G, U, C are present in RNA
Each have H bond donors and acceptors
The sugar forms the backbone on the outside of the molecule and has anti-parallel 5’ to 3’ directionality
DNA properties
Native DNA is a double helix of complementary antiparallel chains
Hydrogen bonding between complementary base pairs (A-T or G-C) holds the two strands together
As the nucleotides stack, phosphodiester bonds between the phosphates above and below create the strand backbone
DNA helix is right handed (B, A, and Z forms exist, but B is the common form)
The two strands are slightly asymmetrically aligned, which results in the major and minor grooves along the double helix structure
The grooves enable factors to interact with the bases during DNA replication and transcription
The unit of length of DNA is the base pair (bp) and there are around 3 billion bp in the human genome and around 20,000-25,000 genes
Eukaryotic DNA
packaged into chromatin (forms 23 pairs of individual chromosomes)
What is the nucleo some
The basic building unit of chromatin is the nucleosome
Nucleosome are composed of what
8 highly basic protein called histone
Dna
‘DNA is wound around the nucleosome with spacing between nucleosomes
DNA follows a hierarchical pathway of folding to form the chromosome. The centromere is a constricted region of the chromosome involved in segregation of chromosomes to daughter cells during DNA replication and cell division
Ends of chromosomes have a highly repetitive G-C rich sequence called the telomere - this non-coding region helps protect the structure of chromosome. Telomeres shorten with successive replications and eventually prevent further replication causing cellular senescence
Nucleoside role
regulation of gene expression, or activity, by determining whether the DNA sequences can be accessed by transcription factors (gene expression)
Enzymatic modification of theamino-terminaltails of histones (e.g. acetylation, methylation, or phosphorylation) modifies the electrical charge and shape
These modifications are physiologically reversible and may prepare the chromatin for DNA replication and transcription
Ribose nuclei’s acid (RNA)
Like DNA is composed of nucleotides, but differs from DNA;
Uracil, adenine and guanine and cytosine
Polymer joined by 3’ to 5’ phosphodiester bonds, but usually single stranded
Can form secondary and tertiary structuters by folding and base-pairing with itself
Some RNAs are capable of catalyzing reactions e.g. peptidyl transferase (involved in translation)
Messenger RNA (mRNA)
Carries genetic information from DNA to the cytoplasm for translation into proteins
Transfer RNA((tRNA)
Has a ‘cloverleaf’ secondary structure and carries individual amino acids for assembly into proteins
Inosine, which is nucleoside modified from adenine is important in tRNA function
Ribosomal RNA (rRNA)
Several rRNAs (5S, 5.8S, 18S, 28S) and accounts for the majority of total RNA in a cell
Intracellular communication:
Cyclic adenosine monophosphate (cAMP) and guanosine monophosphate (cGMP) are intracellular common chemical signalling molecules.
Energy
Adenosine triphosphate (ATP) is a key energy currency of the cell. Guanosine triphosphate (GTP) is also as an energy source in many cellular activities
Energy is stored in the covalent bonds which link the three phosphates
differences between RNA and DNA
Nucleotides in DNA have a 2’ deoxyribose sugar, while nucleotides in RNA have a ribose sugar
RNA has uridine (base: uracil) instead of deoxythymidine (base:thymine) phosphate residues
DNA is usually a double helix, usually in the B form, while RNA is usually single stranded,
Single stranded RNA can fold into diverse structures through regions of internal base pairing and perform similar functions to proteins, including catalysis
Several types of RNA e.g. messenger RNA (transcription), transfer RNA (translation), ribosomal RNA (ribosomes/translation) and others
