MGD 6-7 Flashcards
what is the sequence of molecules to forming genes?
base (GATC)
how does DNA package?
DNA wrapped around histone core of nucleosome
in between are linker DNA of nucleosome
beads on string ^ (genes expressed)
OR solenoid - coiled up tightly - genes not expressed
what are genes and where are they?
genes carry code for proteins and have a chromosomal location
what is the human genome?
the entire DNA sequence of human genome (24 chromosomes - 22 + 2 sex chromosomes X & Y)
what is the structure of DNA? what are polynucleotides?
DNA and RNA are nucleic acids
polynucleotides = linear polymers of nucleotides
what are nucleosides and nucleotides
nucleosides: base + sugar
nucleotide: base + sugar + phosphate (-ve charge)
RNA VS DNA
DNA (deoxy) without oxygen on C2 of pentose sugar
what are the 2 types of nitrogenous bases?
purine: 2 ring (A & G)
pyrimidine: 1 ring (C & T & U)
how do polynucleotides form?
DNA and RNA are polymers
nucleotides are joined via phosphodiester bonds
chain has polarity 5’ to 3’
chain has distinct ends: 5’P and 3’OH
how many bonds does G-C pairing have and A-T/U?
G-C 3 hydrogen bonds
A-U 2 hydrogen bonds
what happens in order for nucleic acids to form duplex structure (helix)
bind in antiparallel 1 chain 5' --> 3' another chain 3' --> 5' strands have to be complementary DNA-DNA, DNA-RNA, RNA-RNA DNA helix is antiparallel
how do RNA stem loops form?
hydrogen bonds are formed between antiparallel, complementary sequences
e.g. tRNA (secondary structures)
how do you read antiparallel, complementary strands of polynucleotides?
top strand: 5’ –> 3’
bottom strand: 3’ –> 5’
left to right
describe the different stages of cell cycle
G1: cell content replication R checkpoint S: DNA replication G2: double check and repair any incorrect DNA sequence cell cycle checkpoint M: mitosis (cell division)
what is DNA replication catalysed by?
DNA polymerase
what are the main points in DNA replication?
separation of DNA strands
stepwise reaction
reaction driven by pyrophosphate hydrolysis
chain growth is directional 5’ –> 3’
what are the 3 main steps in DNA replication?
initiation, elongation, termination
what happens in initiation?
DNA helicase unzips DNA double strand
recognition of origin of replication
requires DNA polymerase
‘kick-start’ by primase attaching to the origin of replciation
what happens in elongation?
bases are attached to the 2 DNA template strands
the bottom strand (3’ –> 5’) produces the leading strand (5’–>3’)
the top strand (5’–>3’) produces lagging strand in okazaki fragments (5’–>3’) which is joined by DNA ligase
because DNA polymerase only extends (adds bases) at 3’ end
what happens in termination?
when DNA ligase anneals the different sections of lagging strand
when 2 facing replication forks meet and DNA ligase joins final fragments
chromosome number stay the same
1 replicated chromosome consist of 2 (sister) chromatids
what is the structure of chromosome?
classical x-shape containing 2 identical DNA molecules
sister chromatids
when does mitosis occur?
cell division for somatic cells
production of 2 identical daughter cells
necessary for some tissue (epidermis, BM, spermatogonia, mucosae)
what are the different phases in mitosis?
interphase, prophase, prometaphase, metaphase, anaphase, telophase, cytokinesis
which stages are interphase?
G1, R check point, S, G2, G2 check point