nucleic acids are large biomolecules that store and transmit hereditary information
DNA:
carries instructions that code for RNA
can self replicate
stores and transmits hereditary information
RNA:
has different forms (rRNA, tRNA, mRNA)
read and translate DNA information (tRNA)
nucleotides have three basic units:
phosphate group
five-carbonsugar (deoxyribose in DNA, ribose in RNA)
a nitrogenous base (A,G,C,T,U)
Purines are nitrogenous bases with two rings in their structure
adenine
guanine
pyrimidines are nitrogenous bases with one ring in their structure
thymine
uracil
cytosine
complementary base pairs
adenine and thymine/uracil (joined by two weak hydrogen bonds)
guanine and cytosine (joined by three hydrogen bonds)
DNA is a long, coiled, double-stranded nucleic acid that forms a doublehelix
RNA is single stranded and are shorter than DNA molecules
histones are proteins in eukaryotic cells that tightly package DNA into structures called nucleosomes
nucleic acids are made up of nucleotides
in DNA the 5 prime end is up and the 3 prime end is down and the double strands are antiparallel
anticodons pair with mRNA codons
genes are region sof DNA that may be translated into a polypeptide or an RNA molecule that can be functional
the genetic code is a set of rules that defines how the information in nucleic acids is translated into proteins and functional RNA molecules
transcription is the production of single-strandedmRNA from DNA
translation is the process where the sequence of an mRNA molecule is used to produce the amino acid sequence of a polypeptide
the genetic code is degenerate because more than one codon can code for the same amino acid - the genetic code uses 4 nucleotides while 3 nucleotides code for an amino acid
structure of eukaryotic genes
promoter region
exons
introns
promoter regions are upstreambinding regions where RNA polymerase attaches to the gene
exons are coding regions of DNA
introns are non-coding regions of DNA
RNA polymerase is needed to separate the double helix in a small section of DNA
gene expression is the process where the information stored in a gene is used to synthesise a functional gene product (RNA or a protein)
triplets are a sequence of 3 nucleotides in genes that corresponds to a specific amino acid in a polypeptide chain
universal - the same triplet will code for the same amino acid in almost all organisms
ribosomal RNA is a structural component of ribosomes
messenger RNA (mRNA) is a single stranded molecule that carries the information from the DNA to the ribosome
transfer RNA bring amino acids in the order specified by the mRNA and rRNA to the ribosomes to help build a polypeptide chain
Protein synthesis has three phases
transcription
RNA processing
translation
Transcription has three phases
initiation - RNA polymerase attaches to the promoter and begins unwinding the double helix, this strand is complementary to te non-template strand (coding strand)
elongation - moving in a 3' to 5' direction, RNA polymerase catalysescondensation polymerisation of free m RNA nucleotides, DNA triplets are being transcribed into RNA codons
termination when RNA polymerase hots the stop codon the mRNA transcript detaches from the RNA polymerase
RNA processing has two steps:
addition of a 5' cap and a poly-A tail to the 5' and 3' end of the pre-mRNA
splicing - introns are removed and exons are spliced together, the mature mRNA moves into the cytoplasm
Transcription and RNA processing occurs in the nucleus and translation occurs in the cytoplasm in a ribosome
Translation has three stages:
Initiation:
Ribosomal subunit attaches to the 5' end of the mRNA molecule and moves along until it finds the start codon
A loaded tRNA molecule with the anti-codon attaches to the codon
A large ribosomal subunit attaches to the tRNA and the small ribosomal subunit
Elongation:
Another loadedtRNA molecule with an anticodon for the next triplet on the mRNA molecule attaches
Amino acids form a hydrogen bond to create a growing polypeptide chain
Unloaded tRNA molecule with the anticodon detaches and leaves
Termination:
Polypeptide chain continues to form until a stop codon is reached
The polypeptide chain is released from the ribosome
alternative splicing is when different combinations of exons form different proteins when some exons are spliced along with the introns
there are three sites for tRNA to bind, aminoacyl site, peptidyl site, exit site
gene expression in eukaryotes can be regulated at any stage of the three stages