chromosomes and cell division

Question 1

What is a Telomere and its function. And what happens to these parts during replication?

Answer 1

tips of the arms/natural ends of chromosomes
function is to protect the ends from DNA repair machinery
they are lost during replication

Question 2

p arm

Answer 2

shorter arm

Question 3

q arm

Answer 3

longer arm

Question 4

heterochromatin

Answer 4

contains the DNA that the chromosome is not currently using- non-active part of the molecule
enables cell to keep it packaged and inaccessible

Question 5

DNA replication

Answer 5

2 DNA strands are unzipped

DNA plymerases copy DNA info and synthesise complementary strand

Question 6

which direction does DNA plymerase synthesis in

Answer 6

5’ to 3’

called continuous

Question 7

3’ to 5’ synthesis

Answer 7

dis-continuous
completed in a series of fragments
called the lagging strand

Question 8

what are the small fragments of DNA made during replication called and what do they need ot be initiated by

Answer 8

okazaki

RNA primer

Question 9

End-replication problem

Answer 9

on the lagging strand there is a gap at the end where the primer has to stop- can’t fully replicate it

Question 10

what is the answer to the end-replication problem?

Answer 10

telomerase
carries out reverse transcriptase
uses RNA template to template new DNA

chromosomes shorten during a number of division and telomerase detects this and extends them

Question 11

kinetochore

Answer 11

protein complex that binds to microtubules

required for chromosome separation during cell division

Question 12

kinetochore

Answer 12

protein complex that binds to microtubules

required for chromosome separation during cell division

Question 13

Chromatin structure

Answer 13

DNA packaged with histone proteins packaged into units called nucleosomes

octamere nucleuosome structure- 8 histone proteins with DNA wrapped round them
locked in place by histone H1

Question 14

Histone proteins

Answer 14

positively charged

small

Question 15

solenoid structure

Answer 15

the structure of the 30 nm fibre. -secondary chromatin structure which helps to package DNA into the nucleus
- 6 nucleosomes in a turn

Question 16

solenoid structure

Answer 16

the structure of the 30 nm fibre which ultimately becomes the chromosome

• secondary chromatin structure which helps to package DNA into the nucleus
• 6 nucleosomes in a turn

Question 17

purpose of packaging DNA

Answer 17

• Negatively charged DNA neutralised by positive charged histone proteins
• DNA takes up less space
• Inactive DNA can be folded into inaccessible locations until required

Question 18

mitosis

Answer 18

IPMAT
interphase
prophase - chromosomes condense, nuclear membrane disappears, spindle fibres form centrioles

metaphase- chromosomes align at equator (metaphase plate), max condensation of chromosomes

anaphase- sister chromatids separate at centromere, move to opposite ends of cell

telophase- new nuclear membranes form- each cell has 46 chromosomes (diploid)

cytokinesis- cytoplasm separates, 2 new daughter cells

Question 19

fluorescent in situ hybridisation (FISH)

Answer 19

a powerful technique used in the detection of chromosomal abnormalities
- uses fluorescent probes that bind to only those parts of the chromosome with a high degree of sequence complementarity for the probes (the probes are complementary to specific parts of chromosome)

Question 20

meiosis

Answer 20

2 rounds of cell division
cell division in germ cells
diploid cells (in ovaries and testes) divide to form haploid cells
chromosomes are passed on as re-arranged copies- allows re-assortment of paternal/maternal genes

Question 21

meiosis process

Answer 21

PMAT-PMAT
essentially the same as in mitosis, except here the non-sister chromatids cross over, forming chiasmata, where they can exchange DNA resulting in variation

the secondary cycle is pretty similar to the first, except the chromosomes are not copied or crossed over. This results in 4 haploid cells being produced instead of 2 diploid cells

Question 22

spermatogenesis (process of sperm formation)

Answer 22

four sperm cells are formed per meiotic cycle, over a course of around 60 days. They undergo many more divisions than eggs, meaning there are more chances for mutations to occur

Question 23

oogenesis (process of egg formation)

Answer 23

Each meiotic cycle produces one ovum and 3 polar bodies and this process occurs over 10-50 years.
These polar bodies mature into ova.

Question 24

x-inactivation

Answer 24

genes present on X chromosome- one needs to be switched off, random inactivation of one in early embryo
so that women don’t make twice as much of proteins encoded by X chromosome genes

Question 25

What 3 types of chromosome abnormalities are there?

Answer 25

numerical structural mutational

Question 26

numerical abnormalities and name the different autosomal and sex chromosome aneuploidy syndromes.

Answer 26

having too many or too little a number of chromosome pairs ie having more or less than 23 autosomal: Trisomy 21, Trisomy 18, Trisomy 13 sex chromosome: X and XXY

Question 27

Trisomy 21

Answer 27

``` DOWN SYNDROME autosomal Trisomy 21 is a type of numerical chromosome abnormality 95% caused by non-dysjunction can cause an IQ of less than 50 Alzheimer's later in life ```

Question 28

what is non-dysjunction?

Answer 28

homologous chromosomes or sister chromatids not separating

Question 29

Trisomy 13

Answer 29

PATAU SYNDROME autosomal very few survive past first year of life 90% non-dysjunction

Question 30

Trisomy 18

Answer 30

``` EDWARD SYNDROME autosomal 90% non-dysjunction most die within first month to a year of life cut 8 in half = E for edward ```

Question 31

X

Answer 31

Turner syndrome sex chromosome aneuploidy- affects females- 1 less X chromosome results in neck webbing and widely spaced nipples intelligence and lifespan are normal about 97% of babies affects are miscarried or still born but quite rare syndrome 1 in 1500 to 2500

Question 32

XXY

Answer 32

``` Klinefelter syndrome affects males- additional X chromosome long limbs infertile, small testes 50% develop breasts mild learning difficulties ```

Question 33

Structural abnormalities include?

Answer 33

``` balanced and unbalanced rearrangements translocation deletion insertion inversion ```

Question 34

translocation- balanced and unbalanced

Answer 34

``` balanced= piece of DNA or chromosome breaks off from two chromosomes and swaps to from two new structurally rearranged chromosomes unbalanced= only one breaks off and swaps ```

Question 35

deletion

Answer 35

lost part of chromosome

Question 36

insertion

Answer 36

addition of larger sequence of DNA into chromosome

Question 37

inversion: peri-centric and para-centric

Answer 37

rearrangement piece of chromosome breaks off, turns around and then is reinserted peri-centric:-both sides of centromere para-centric:- only at one side of centromere

Question 38

Robertsonian translocation

Answer 38

fusion of two acrocentric (centromere is close to the end of chromosome) chromosomes no loss of genetic info loss of short arms

Question 39

Mutational abnormalities: somatic and germline?

Answer 39

germline- mutations in germ cells- passed on to children | somatic- occurs after contraception in any of the cells in the body except germ cells

Question 40

types of mutations?

Answer 40

non coding- doesn't affect amino acid sequence/protein | coding- silent, missense, nonsense, frameshift

Question 41

Silent mutation

Answer 41

no change in amino acid or protien

Question 42

missense mutation

Answer 42

changes one of the RNA codons so amino acid sequence is altered- different protein

Question 43

nonsense

Answer 43

stop codon is produced

Question 44

frameshift

Answer 44

addition or deletion of base pair in DNA so translation is altered/ shifted from that point

Question 45

Point mutation

Answer 45

only affects 1 or very few nucleotides in a gene sequence

Question 46

Point mutation

Answer 46

only affects 1 or very few nucleotides in a gene sequence

Question 47

Methods of detecting mutations

Answer 47

``` PCR DNA sequencing Gel electrophoresis ARMS RFLP ```

Question 48

PCR

Answer 48

in vitro (out of the body, lab etc) amplifies DNA heating and cooling stages

Question 49

gel electrophoresis

Answer 49

separates DNA fragments by size by applying electric field DNA is negatively charged agarose gel matrix

Question 50

DNA sequencing

Answer 50

determining order of nucleotides in DNA sequence very sensitive, robust gold standard however expensive

Question 51

what type of mutation is down syndrome caused by

Answer 51

translocation an unbalanced translocation of chromosome 21 can lead to having 3 copies of the long arm It is more commonly caused by trisomy for the whole of chromosome 21

Question 52

chromosome staining with dyes? what happens

Answer 52

When chromosomes are stained with dyes, they appear to have alternating lightly or darkly stained regions. The lightly stained regions are euchromatin and contain genetically active DNA. The dark regions are heterochromatin and are inactive DNA. (think dark, lights off, inactive)

Question 53

when does gametogenesis in males occur? and how many divisions occur?

Answer 53

during puberty

Question 54

when does gametogenesis in females occur? how many divisions occur?

Answer 54

in the fetus

Question 55

which parent is mitochondrial DNA passed on by?

Answer 55

Mother | this is because the egg is bigger and has more space for mitochondria

Question 56

when can you only see chromosomes?

Answer 56

when they are dividing

Question 57

what are mismatch repair (MMR) genes?

Answer 57

they correct errors that spontaneously occur during DNA replication

Question 58

who do Y-linked conditions occur to only?

Answer 58

only in males and in all their male descendants