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
what happens in prophase?
chromosome decondenses (out of solenoid (heterochromatin) into beads on string - euchromatin), nuclear envelope breaks down, spindle fibres form
what happens in prometaphase?
spindle fibres attach to kinetochore of centromere
what happens in metaphase?
chromosomes align in the equator of the cell (at metaphase plate)
What happens in anaphase?
sister chromatids (daughter chromosomes) are pulled to opposite ends of the cell via kinetochore (centromere divides)
What happens in telophase?
spindle fibres disintegrate
nuclear envelop reforms
chromosomes decondense
what happens in cytokinesis?
cytoplasm divides
parent cell becomes 2 daughter cells with identical genetic information
what is meiosis?
special cell division for germ line cells
production of 4 non-identical cells (1/2 chromosome)
1 round of replication followed by 2 rounds of division
diploid (2n) reduced to haploid (n)
production of eggs and sperm
what are the steps in meiosis?
prophase I, genetic recombination through crossing over, metaphase I, anaphase I, telophase I, prophase II, metaphase II, anaphase II, telophase II + cytokinesis
what is prophase I?
line up with homologous pair (1 from mum, 1 dad) independent assortment (4n) in equator (random assortment)
what happens between prophase I and metaphase I?
genetic recombination: crossing over
what is metaphase I?
spindle attach to kinetochores, homologous pairs line up in the equator of the cell
What is anaphase I?
homologous pairs of chromosome pulled to opposite poles
what happens in telophase I?
spindle disappears, nuclear membrane reforms, starts to split into 2 cells (2n) cytokinesis
what happens in prophase II?
2 daughter cells: spindles attach to kinetochores
what happens in metaphase II?
chromosomes line up in equator of cell
what happens in anaphase II?
chromatids (sister) pulled to opposite poles
What happens in telophase II + cytokinesis?
cells split, 23 chromatids each (1/2 single chromosome) n 4 x cells
What are the consequences of meiosis?
- maintaining constant chromosome number of from generation to generation (23 Pairs)
- generation of genetic diversity
random assortment of chromosomes
crossing over of genetic material
what is spermatogenesis and what does it produce and how long does it take?
cell division to produce male gametes
1 spermatocyte (2n) –> 4 sperm (n)
takes 48 days
what is oogenesis, what does it produce and how long does it last for?
cell division to produce female gametes
1 oocyte (2n) –> 1 egg (n) + 3 polar bodies
lasts 12-50 years
what are the consequences of faulty meiosis?
1/3 of all identified miscarriages
infertility
leading cause of mental retardation
