VIII - Genetics Flashcards
Central Dogma
Replication → Transcription → Translation
Polymer composed of nucleotide builduing blocks, chemical basis of heredity, grouped into genes which are the fundamental units of genetic information, double helix structure with major and minor grooves, contained in the cytoplasm of prokaryotes and the nucleus of eukaryotes
Deoxyribonucleid Acid (DNA)
Deoxynucleotides covalently linked by 3’,5’-phosphodiester bonds
DeoxyAdenylate, DeoxyGuanylate, DeoxyCytidylate, Thymidylate
5’-OH group attached to 3’-OH group, gives strands directionality, bonds are cleaved hydrolytically by chemicals or hydrolyzed enzymatically by exonucleases or endonucleases
3’-5’ Phosphodiester Bonds
Enzymatically cleaves phosphodiester bonds at the ends
Exonucleases
Enzymatically cleaves phosphodiester bonds in the middle
Endonucleases
Strands that run in opposite directions
Antiparallel Strands
Held together by hydrogen bonds and hydrophobic interactions, adenine to thymine, guanine to cytosine
Complementary Base airing
In any sample of dsDNA the amount of adenine equals the amount of thymine and the amount of guanine equals the amount of cytosine, total amount of purines equals total amount of pyrimidines
Chargaff’s Rule
Temperature at which one half of the helical structure is lost (denaturation)
Melting Temperature
DNA: right-handed helix with 10 residues per 360° turn
B-DNA
DNA: moderately dehydrated B form, right-handed with 11 base pairs per turn
A-DNA
DNA: left-handed helix that contains about 12 base pairs per turn, alternating purines and pyrimidines
Z-DNA
Five classes of small, positively charged proteins that form ionic bonds with negatively charged DNA
Histones
2 each of histones H2A, H2B, H3 and H4 form a structural core around which DNA is wrapped creating a
nucleosome
The DNA connecting the nucleosomes is called _____ and is bound to histone ___.
linker DNA, H1
Further packing of DNA due to hydrophobic interactions and in association with other non-histone proteins compacts it into
chromatin
Chromatin: densely packed and transcriptionally inactive during interphase, observed by electron microscopy
Heterochromatin
Chromatin: transcriptionally active that stains less densely
Euchromatin
Nucleofilament, nucleosomes that are packed more tightly, organized into loops that are anchored by a nuclear scaffold containing several proteins
Polynucleosome
DNA: coding regions are interrupted by
intervening sequences
DNA: more than half of eukaryotic DNA is
unique, non-repetitive
DNA: at least 30% of the genome consists of
repetitive sequences
DNA: 1% of cellular DNA is in the
mitochondria
Occurs in the S phase of the cell cycle, semi-conservative
DNA Replication
DNA synthesis begins at a short sequence composed almost exclusively of AT base pairs
Origin of Replication
DNA Synthesis: strands are separated locally forming two
replication forks
DNA Synthesis: Sequence of Enzymes
DNA A Protein → Helicase → Single-Stranded DNA-Binding Proteins → DNA Topoisomerases → Primase → DNA Polymerase III → DNA Polymerase I → Ligase
DNA Synthesis: group of proteins that recognize the origin of replication
DNA A Protein
DNA Synthesis: unwinds the double helix ahead of the advancing replication fork
Helicase
DNA Synthesis: maintain the separation of the parental strands
Single-Stranded DNA-Binding Proteins
DNA Synthesis: remove supercoils that interfere with the further unwinding of the double helix
DNA Topoisomerases
DNA Topoisomerases: cleaves 1 strand
Swivelase (Type I)
DNA Topoisomerases: cleaves both strands, target of quinolone antibiotics
Gyrase (Type II)
DNA Synthesis: synthesize short stretches of RNA called primers, needed by DNA polymerase to begin DNA chain elongation
Primase
DNA Synthesis: catalyzes chain elongation using 5’-deoxyribonucleoside triphosphates as substrates, proofreads the newly synthesized DNA using its 3’→5’ exonuclease activity
DNA Polymerase III
DNA polymerases are only able to read the template in the _____ direction and synthesize in the _____ direction
reads 3’→5’, synthesizes 5’→3’
DNA Synthesis: fragments of the lagging strand
Okazaki Fragments
DNA Synthesis: removes RNA primers using its 5’→3’ exonuclease activity and fills the resulting gaps
DNA Polymerase I
DNA Synthesis: seals the nicks between Okazaki fragments and catalyzes the final phospholipid ester linkage
Ligase
Prokaryotic Polymerases: gap filling and synthesis of lagging strand
Polymerase I
Prokaryotic Polymerases: DNA proofreading and repair
Polymerase II
Prokaryotic Polymerases: processive, leading strand synthesis
Polymerase III
Eukaryotic Polymerases: gap filling and synthesis of lagging strand
Polymerase α
Eukaryotic Polymerases: DNA proofreading and repair
Polymerase ε
Eukaryotic Polymerases: DNA repair
Polymerase β
Eukaryotic Polymerases: mitochondrial DNA synthesis
Polymerase γ
Eukaryotic Polymerases: processive, leading strand synthesis
Polymerase δ
Sequence of DNA Replication in Eukaryotes
identification of the origins of replication → unwinding (denaturation) of dsDNA to provide an ssDNA template → formation of the replication fork → initiation of DNA synthesis and elongation → formation of replication bubble with ligation of the newly synthesized DNA segments → reconstitution of chromatin structure
Stretches of highly repetitive DNA found at the ends of linear chromosomes, as cells divide and age, these sequences are shortened contributing to cell death
Telomeres
Replace the telomeres in cells that do not age
Telomerase
Retroviruses such as HIV carry their genomes in the form of ssRNA molecules, used to make a DNA copy of RNA, integrates the copy into the host cell DNA, lacks proofreading, contributes to high mutation rate
Reverse Transcriptase
DNA Repair: mismatched strand, escaped proofreading
identification of the mismatched strand, endonuclease nicks the mismatched strandd and the mismatched base is removed, DNA polymerase I and DNA ligase complete the repair
DNA Damage: Hereditary Non-Polyposis Colon Cancer
mismatched strand, escaped proofreading
DNA Repair: thymine dimers due to exposure of a cell to UV light, prevents DNA from replicating beyond the dimer
removed by UV specific endonucleases (uvrABC excinuclease) and the resulting gap is filled by DNA Polymerase I
DNA Damage: Xeroderma Pigmentosum
thymine dimers due to exposure of a cell to UV light, prevents DNA from replicating beyond the dimer
DNA Repair: abnormal bases, either spontaneous or due to the action of deaminating or alkylating compounds
Specific glycosylases recognize the abnormal bases and cleave them hydrolytically from the deoxyribose-phosphate backbone, leaving an apyrimidinic or apurinic (AP) site, AP-endonucleases make a nick at the 5’-side of the AP site, deoxyribose-phosphate lyase removes the single empty sugar-phosphate residue, DNA polymerase and DNA ligase complete the repair
DNA Repair: recognize the abnormal bases and cleave them hydrolytically from the deoxyribose-phosphate backbone, leaving an apyrimidinic or apurinic (AP) site
Glycosylases
DNA Repair: make a nick at the 5’-side of the AP site
AP-Endonucleases
DNA Repair: removes the single empty sugar-phosphate residue
Deoxyribose-Phosphate Lyase
DNA Repair: copying errors (single base or 2-5 base unpaired loops), methyl-directed strand cutting, exonuclease digestion and replacement
Mismatch Repair
DNA Repair: methyl-directed strand cutting, exonuclease digestion and replacement
Mismatch Repair
DNA Repair: spontaneous, chemical or radiation damage to a single base
Base Excision Repair
DNA Repair: base removal by N-glycosylase, abasic sugar removal and replacement
Base Excision Repair
DNA Repair: spontaneous, chemical or radiation damage to a DNA segment
Nucleotide Excision Repair
DNA Repair: removal of an approximately 30-nucleotide oligomer and replacement
Nucleotide Excision Repair
DNA Repair: ionizing radiation, chemotherapy, oxidative free radicals
Double-Strand Break Repair
DNA Repair: synapsis, unwinding, alignment, ligation
Double-Strand Break Repair