Chromosomes Flashcards
Cell Cycle & Chromosome Structure + Chromatin and Karyotypes + Meiosis and X Inactivation
<p>What does each eukaryotic chromosome contain?</p>
<p>Linear chromosomes</p>
<p>Telomere</p>
<p>Centromere</p>
<p>Heterochromatin</p>
<p>Euchromatin</p>
<p>What does the centromere do?</p>
<p>Hold the chromosome together</p>
<p>What are telomeres?</p>
<p>The ends of DNA which need to be protected because when DNA gets damaged cells have mechanisms to repair it and so need to recognise blunt ends, important do not try to repair natural ends of chromosomes</p>
<p>Why do telomeres need to be protected?</p>
<p>To prevent cells trying to repair natural ends of chromosomes, they recognise blunt ends</p>
<p>What is the process of DNA replication?</p>
<p>1) Strand unwinds and hydrogen bonds connecting bases are broken</p>
<p>2) RNA primer initiates DNA synthesis</p>
<p>3) DNA polymerase copies the information and makes a complimentary strand (daughter strand on each new DNA)</p>
<p>4) Lagging strands need to be initiated by RNA primer and connected by DNA ligase</p>
<p>In what direction does DNA polymerase add new nucleotides?</p>
<p>5' to 3' direction</p>
<p>What are okazaki fragments?</p>
<p>The sections of DNA present on the lagging strand that need to be connected</p>
<p>How much base pairs are lost during mitosis and why?</p>
<p>100 base pairs are lost each time due to the gap at the end of the lagging strand due to the primer</p>
<p>What happens when chromosomes become to short due to bases being lost during each mitosis cycle?</p>
<p>They are recognised by telomerase and become extended</p>
<p>What is mitosis?</p>
<p>Cell division that results in two daughter cells that have the same number of chromosomes as the parent cell</p>
<p>What are the phases of mitosis?</p>
<p>1) Prophase</p>
<p>2) Metaphase</p>
<p>3) Anaphase</p>
<p>4) Telophase</p>
<p>5) Cytokinesis</p>
<p>What happens during prophase?</p>
<p>Chromosomes condense</p>
<p>Nuclear membrane disapears</p>
<p>Spindle fibres form from the centriole</p>
<p>What happens during metaphase?</p>
<p>Chromosomes aligned at the equator of the cell</p>
<p>Attached by fibre to each centriole</p>
<p>Maximum condensation of chromosome</p>
<p>What happens during anaphase?</p>
<p>Sister chromatids seperate at centromere</p>
<p>Seperate longitudinally</p>
<p>Move to opposite ends of the cell</p>
<p>What happens during telophase?</p>
<p>New nuclear membrane forms</p>
<p>Each cell contains 46 chromosomes (diploid)</p>
<p>What happens during cytokinesis?</p>
<p>Cytoplasm seperates</p>
<p>Two new daughter cells</p>
<p>During what phase are chromosomes most condensed?</p>
<p>Metaphase</p>
<p>In what phase can chromosomes be seen?</p>
<p>Prophase</p>
<p>What is the spindle made from?</p>
<p>Microtubules</p>
<p>What do centromeres do during mitosis?</p>
<p>Join sister chromatids and bind to microtubules</p>
<p>What is the site of kinetochore?</p>
<p>Centromeres</p>
<p>What are centromeres composed of?</p>
<p>Repeated DNA sequences known as satellite DNA</p>
<p>What is satellite DNA?</p>
<p>DNA that does not code, but forms the site of kinetochore</p>
<p>What is kinetochore?</p>
<p>Multiprotein complex that attaches to microtubules from each pole</p>
What do both sides of kinetochore need to be captured?
So that each daughter cell has the same amount of chromosomes
What are the 2 forms of chromatin?
Heterochromatin
Euchromatin
Which is heterochromatin and euchromatin is condensed with silent genes and open with active genes?
Heterochromatin is condensed with silent genes
Euchromatin is open with active genes
What is chromatin?
The part of a chromosome that contains the coding information
Why can euchromatin code for proteins?
Open structure can be accessed by RNA polymerase
How many base pairs are there in our genome?
3 billion
What are extragenic sequences?
DNA that is repeated
What kind of sequences are lots of our DNA?
Extragenic sequences
What are the 2 kinds of extragenic sequences?
Tandemly repeated DNA sequences
Highly repeated interspersed DNA sequences
What are examples of tandermly repeated DNA sequences?
Satellite DNA
Minisatellite DNA
What are examples of highly repeated interspersed DNA sequences?
SINEs (short interspersed nuclear elements)
LINEs (long interspersed nuclear elements)
How much of our DNA is repeated sequences?
A huge amount
What are nucleosomes?
Formed from the packaging of DNA and histone forming chomatin
How many base pairs are around a core of a nucleosome?
146 base pairs (1.8 turns)
What is the core of a nucleosome made of?
8 histones
How many different kinds of histone proteins are there?
4
What charge do histones have?
Positive charge
What are nucleosome further wrapped to form?
'Solenoid' structures
What does the further wrapping of nucleosomes compact DNA by a factor of?
40
What are the 4 levels of condensing chromatin structure?
Level 1 (nucleosome)
Level 2 (chromatin fibre)
Level 3 (fibre-scaffold complex)
Level 4 (chromosome)
Why does DNA and histine combine?
Negatively charged DNA is neutralised by positvely charged histone
Why is DNA packaged?
Negatively charged DNA is neutralised by positively charged histone
DNA takes up less space
Inactive DNA can be folded into inaccessible locations until required
What locks DNA in place in the nucleosome?
Histone H1
What is a karyotype?
Number and appearance of chromosomes
What is the process of viewing a karyotype?
1) Blood extracted
2) Red blood cells seperated
3) Add culture medium to white cells and incubate for 3 days at 37oC
4) Add colchicine
5) Seperate white cells
6) Add hyptonic saline
7) Spread cells onto slide and stain
8) Photograph and produce karyotype
How do male and female chromosomes differ?
Males have a X and a Y chromosome
Females have two X chromosomes
Where are the chromosomes from each pair from?
One is from the mother and one is from the father
What are the 3 types of chromosomes in a karyotype?
Metacentric (P and Q arms are the same length)
Sub metacentric (P arm is shorter than the Q arm)
Acrocentric (P arm is so short that is is not functional)
What are the P and Q ares like in metacentric chromosomes?
The same length
What are the P and Q arms like in submetacentric chromosomes?
P arm is shorter than the Q arm
What are the P and Q arms like in acrocentric chromosomes?
The P arm is so short it is not functional
What can be used to life up specific sequences of interest?
Fluorescent in situ hybridisation (FISH)
What are the different kinds of fluorescent in situ hybridisation probes?
Unique sequence probes
Centromeric probes
Telomeric probes
Whole chromosome probe
What is the centromeric probe used for?
Determining chromosome number
What is the telomeric probe useful for?
Detecting subtelomeric rearrangments
What is the whole chromosome probe useful for?
Detecting translocation and rearrangements
What are probes unique to?
Specific genes
What is a spectral karyotype?
A karyotype where each chromosome pair is labelled a different colour
What is meiosis?
Cell division in germ cell
What are diploid cells?
Cells that have two complete sets of chromosomes (46 chromosomes)
What are haploid cells (gametes)?
Contains 23 chromosomes
What happens during meiosis?
1) Diploid cells in the ovaries and testis divide to form haploid cells
2) Chromosomes are passed on as rearranged copies which creates genetic diversity (paternal and maternal chromosomes exchange parts)
What is oogenesis?
Process of egg formation
What is spermatogenesis?
Process of sperm formation
Why is there more of a chance for a mutation in sperm than eggs?
Sperm goes through more cell divisions than eggs do
What is gametogenesis?
The process in which cells undergo meiosis to form gametes
What is formed by meiosis from one cell in a male?
4 gametes (sperm)
What is formed by meiosis from one cell in a female?
One egg and three polar bodies
When does male gametogenesis commence?
Puberty
When does female gametogenesis commence?
Early embryonic life
How long goes male gametogenesis take?
60-65 days
How long does female gametogenesis take?
10-50 years
How many mitosis occur in gamete formation in males?
30-500
How many mitosis occurs in gamete formation in females?
20-30
What is the gamete production per meiosis in males?
4 spermatids
What is the gamete production per meiosis in females?
1 ovum and 3 polar bodies
What is the gamete production in men?
100-200 million per ejaculation
What is the gamete production in females?
1 ovum per mentrual cycle
What is fertilisation?
Two haploid cells (egg and sperm) form 1 diploid cell (zygote) which develops into an embryo
What determines whether the embryo is male or female?
Whether the sperm contains a X or a Y chromosome
Where does the mitochondria in a embryo come from?
Mother because the egg is where most of the cytoplasmic fluid is from
What happens to the X chromosomes in a zygote if they have two?
Both are active, but in early embryonic life one X chromosome is randomly switched off
What do chromosome abnormalites result due to?
Too many chromosome
Too little chromosomes
Insertion
Translocation
Deletion
Duplication
Inversion
