1: Chromosomes, DNA, Nucleotides, DNA replication, Mitosis and Meiosis

processes that generates genetic diversity in meiosis

independent assortment of chromosomes (meiosisI) and crossing over

meiosis 1 vs meiosis 2

meiosis 1 homologous chromosomes of each chromosome pair are divied. during meiosis 2 chromatids of each chromosomes are divided

what is the cell cycle

process by which cells replicate their DNA and divide into daughter cells. control of cell cycle ensures regulated proliferation (this regulation can be lost in some diseases eg cancer)

4 phases of cell cycle and describe what happens

G1: cell prepares for DNA replication

S: DNA replication

G2: cell prepares for division

M: mitosis or cell division

at which points in the cell cycle are the checkpoints which control progression of the cell through the division process

G2 to M; G1 to S

Compare and contrast the processes of mitosis and meiosis. List three similarities and three differences between the processes. Consider the number of phases and divisions, number of daughter cells, role of the process, location of the process.

similarities:both involve cell divisions, similar stages within each round, both begin with DNA replication

Differences: mitosis 1 division meiosis 2; mitosis 2daughter cell meiosis 4; meiosis for gamete production vs mitosis for grwoth/repair; mitosis somatic but meiosis gonads

male infertility and meiosis

meiotic abnormailities in chromosome pairing, meiotic progression, meiotic recombination. 1/2 no meiotic cells. with meiotic cells: progression of meiosis is altered with significantly more cells observed in early stages of prophase. suggests difficulties in pairing and synapsis of homologous chromosomes

chromosomes prone to non-disjunction

chromosomes 21, 22, X and Y. 2-3 fold ^ in aneuploidy levels for these chromosomes compared to other chromosomes

A couple presents to a fertility clinic as they were unable to achieve pregnancy after one year of unprotected intercourse. The male partner is 29 years old with negative medical history. Examination is unremarkable. Genetic analysis of the sperm show no obvious abnormalities but the man has a low sperm count

if meiotic arrest was occurring in this pt, what processes would be impaired?

anything that stimulates meiosis 1. spindle formation, formation of the tetrad and homologous recombination

low sperm count common cause

meiotic arrest ie no maturation beyond spermatocytes.

explain why meiotic arrest leads to infertility

no maturation past spermatocytes. 2n precursor of 4spermatids. without maturation therefore no sperm can be created. no sperm no fertilisation. male is infertile

Non-disjunction

failure of homologous chromosomes or sister chromatids to separate properly in cell division

nondisjunction meiosis 1 result

daughter cell of meiosis 1 is affected. therefore both daughter cells produced in meiosis 2 upon cell division will be affected. one with extra chromosome the other missing a chromosome. therefore upon division, gamete daughter cell pairs will be n+1 and n-1

nondisjunction of meiosis 2

only daughter cell after meiosis 1 is affected. therefore when this daughter cell undergoes a second round of division, only one pair of gamete daughter cells are affected (ie n+1, n-1)

explain acelarated growth rate of cancers at the cellular level

cells divide by mitosis and in cancer the cell checkpoints have been removed so multiple uncontrolled rounds of mitosis can occur quickly giving rise to tumours.

what steps might be taken to preserve jack's fertility prior to chemotherapy

sperm banking

name a drug used to treat metastatic testicular cancer that interferes with elongation stage of DNA replication

BCNU, cisplatin

name a drug used to treat cancers that interferes with the termination stage of DNA replication

AraC, 6-MP

hypothesise why chemo may lead to infertility in men being treated for testicular cancer

kills germ cells which is why it is a strong treatment. sperm cells are generated by germ cells. therefore heavy reduction in sperm cells usually semen contains zero sperm during (azoospermia)

2 types of nitrogenous bases found in DNA and RNA

cytosine, adenine

nitrogenous bases in DNA and RNA

ATCG and AUGG

what do ATCGU stand for

Uracil, adenine, thymine, cytosine, guanine

components of a nucleotide

pentose sugar, phosphate group, nitrogenous base

nucleotide pairing

phosphate, deoxyrubose sugar, nitrogenous base.

Covalent bonding sugar base is backbone of strand.

Each sugar attaches repetitively to 2 phosphates 3 1(3 prime carbon) to 5 1 ( 5prime carbon)

Adenine(A) pairs with Thymine(T) Guanine (G) pairs with Cytosine (C).

An antiparallel arrangement runs in opposite direction of other. 5 1 to 3 1 to 3 1 to 5 1.

This is significant to DNA and protein production.

DNA packaging

DNA double helix tightly around histones to form nucleosomes, which form beads on a string DNA. nucleosomes tightly packed into solenoid structures forming 30nm fibres. these fibres compacted into several hierarchical loops to form highly condensed structures which are the chromosomes visible under light microscopes in the nucleus during cell division.

Purines

two ring structure Adenine and Guanine

Pyrimidines

one ring structure. C T U.

nucleotide NTP to polynucleotide with?

GTP, CTP, ATP

nucleotide dNTP to polynucleotide with?

dCTP, dGTP, dTTP

how many purines can be found in a stretch of 100bp double stranded DNA

100

complementary sequence for 5'GGGATTCC

5'GGAATCCC

In the DNA sequence TTGCCCA base G is connected with a covalent bond to...

base C and T on same strand

In the DNA sequence TTGCCCA base G is connected with a covalent bond to...

OH group

Many molecular laboratory techniques that are used to investigate DNA, such as Southern hybridisation and Polymerase Chain Reaction (PCR) use high temperature to split double-stranded DNA into single-stranded DNA. Which bonds within double-stranded DNA helix are broken under these conditions.

A-T h bonds and C-g h bonds

Chromatin

dna/protein complex forms a chromosome

In the DNA sequence TTGCCCA base G is connected with a covalent bond to...

deoxyribose

The single stranded DNA molecule with the sequence GCTGGATGAA is a polar molecule. The sequence is written according to the normal convention. What is at the 5' end of the sequence?

phosphate group

heterochromatin

solanoid fibres. genes not expressed

Eurochromatin

beads on a string. expressed

adenine in DNA and RNA

deoxyadenoSInemonophosphate (dAMP). purine. in RNA same but without deoxy

guanine in DNA and RNA

deoxyguanoSInemonophosphate (dGMP). purine. in RNA same but without the deoxy

cytosine in DNA and RNA

deoxycytoDInemonophosphate (dCMP). pyrimadine. same in RNA but without the deoxy

Thymine in DNA

deoxythymiDInemonophosphate (dTMP) pyrimadine

Uracil in RNA

uriDInemonophosphate (UMP)

cell cycle checkpoint that determines mieosis or mitosis

end of G2

initiation DNA replication

helicase unwinds the helix. single stranded binding proteins bind to the strand to stop the helix reforming. primase binds to the strand and adds polynucleotide to 3' end

DNA replication elongation

Primase removed and nucleotides added to the polynucleotides (that were added by primase) by DNA polymerase at 3' end forming a continuous strand of replication. Other side of alpha helix runs in opposite direction however DNA polymerase can only add in 5' to 3' direction therefore cannot have continuous production. Therefore, primase attaches on template strand at various points and adds small fragments of DNA (okazaki fragments) which are then bound together by ligase.

DNA replication termination

2 new strands are formed

cancer drug inhibits elongation of DNA

cisplatin and BCNU used to treat metastatic testicular cancer and leukaemia.

cancer drug inhibits termination of DNA

AraC and 6-MP used to treat acute leukaemia

different forms of chromosome structure

metacentric, submetacentric, acrocentric, telocentric

importance of crossing over

increases genetic diversity and failures are associated with moving chromosomes to wrong location