GENETICS

Molecular Genetics

central dogma

the transmission of information through DNA, RNA, and proteins

DNA

the basis for heredity, can self-replicate, is mutable and is passed down through generations (basis for evolution)

nucleotide

composed of a sugar bonded to both a phosphate group and a nitrogenous base

purines

adenine and guanine, double rings

pyrimidines

cytosine, thymine, uracil, single rings

two hydrogen bonds

adenine and thymine

three hydrogen bonds

cytosine and thymine, cytosine and uracil

watson-crick DNA model

double helix, discovered DNA structure with help of Rosalind Franklin, antiparallel - 5’ end and 3’ end

DNA replication

1. DNA helicase - unwinds double helix, breaks H bonds between nitrogenous bases, creates the replication fork

2. DNA polymerase - uses parent strand as template and creates daughter strand, can only add nucleotides to 3’ end of DNA strands

3. DNA ligase - seals gaps between okazaki fragments

replication fork

opening in the DNA molecule, creates torsional strain as DNA is unwound

topoisomerase

removes torsional strain in unwound DNA by cutting, twisting, and rejoining the strands of DNA

replication bubble

where the two DNA strands are separated, each single strand acts as a template

semiconservative replication

each parent strand acts as a template, each new helix has one parent strand and one daughter strand

DNA polymerase

creates daughter strand 5’ to 3’ (reads parents strand 3’ to 5’)

leading strand

3’ end towards replication fork, allows for continuous synthesis, one RNA primer

lagging strand

3’ end away from replication fork, discontinuous synthesis in okazaki fragments, requires multiple RNA primers

DNA ligase

seals gaps between okazaki fragments

DNA coding strand

same as mRNA transcript, but Ts instead of Us

DNA template strand

will be complimentary to the mRNA transcript

processes that occur 5’ to 3’

DNA synthesis, DNA repair, RNA transcription, RNA translation/codon reading

RNA

ribonucleic acid, similar to DNA, found in the nucleus and cytoplasm, many types (mRNA, tRNA, rRNA), ribose is sugar, uracil instead of thymine, usually single stranded

messenger RNA (mRNA)

carries the complement of a DNA sequence, carries info from nucleus to ribosomes for protein synthesis, complementary to the DNA template strand, identical to coding strand (U instead of T)

monocistronic

one mRNA strand codes for one polypeptide

transfer RNA (tRNA)

small RNA found in the cytoplasm, assists in translation, recognizes both the mRNA codon and its corresponding amino acid, at least one type for each amino acid (40 known types)

anticodon

found on one end of a tRNA, a 3 nucleotide sequence, complementary to mRNA codons (amino acid attaches to the other end)

aminoacyl-tRNA synthetase

one enzyme for each amino acid, active site binds to both the amino acid and its corresponding tRNA

charged tRNA

when a tRNA is complexed with the appropriate amino acid

ribosomal RNA (rRNA)

synthesized in the nucleolus of eukaryotes and the cytoplasm of prokaryotes, an integral part of ribosomal machinery used during protein assembly in the cytoplasm, most abundant RNA type in the cell

transcription

RNA polymerase binds to DNA template strand at a promoter region after DNA bas been opened by helicase and topoisomerase, reads DNA in 3’ to 5’ and creates RNA strand 5’ to 3’

promoter region

a short DNA sequence found upstream from the transcription start site, RNA pol binds with help of transcription factors

TATA box

most common promoter site in eukaryotes, 30 bp upstream, TATAAT

pribnow box

most common promoter site in prokaryotes, 10 bp upstream, TTGACA

heteronuclear RNA (hnRNA)

aka pre-RNA, RNA that has not been processed yet, contains introns and exons, RNA is termed mRNA after processing and can leave the nucleus

introns

extra sequences that are spliced out/removed by a spliceosome

exons

kept nucleotides, necessary to make protein

5’ guanine cap

protects mRNA from degradation by nucleases, interacts with ribosome to enhance translation

3’ poly a tail

~250 adenylates at the 3’ end of the RNA, enhances stability and translation efficiency, also involved in nuclear transport

codons

help translate the nitrogenous base message in mRNA to the language of amino acids/proteins, 3 nucleotide sequences of mRNA that correspond to a specific amino acid