Cell cycle + cell division, DNA & genetics

What is Mendel's Law of Segregation?

Alleles pairs separate during gamete formation, and reunite randomly at fertilization

What is epigenetics?

The presence of methyl groups attached to DNA bases controls the expression of genes and changes cellular behaviour.

What influences methylation status? (3)

Aging

Diseases - cancer

Environmental factors - diet

What is the function of single-strand binding proteins in DNA replication?

It helps to form the central nucleoprotein complex substrate for DNA replication, recombination, and repair processes

What is the function of the single strand binding protein in DNA replication?

the single-stranded DNA binding protein (SSB) wraps single-stranded DNA (ssDNA) with high affinity to protect it from degradation and prevent secondary structure formation

What is the function of RNA polymerase (RNA primase) in DNA replication?

Synthesises RNA primers during DNA replication

What is the function of DNA polymerase in DNA replication?

Joins individual nucleotides to produce a new strand of DNA

What is the function of DNA ligase in DNA replication?

catalyse the formation of phosphodiester bonds between the two ends in the backbone of double-stranded DNA

What is DNA gyrase?

-A topoisomerase II enzyme

What is the function of DNA gyrase?

-Causes a double strand break and loops one strand under another

- its critical target for blocking cell replication of antibiotics and antineoplastic

What is the function of DNA helicase?

DNA helicase breaks the hydrogen bonds between complimentary base pairs

What enzyme synthesises the short RNA chain called a primer

primase

How is DNA synthesised?

Addition of nucleotides along one strand

called the leading strand. DNA polymerase reads 3'

What is the other daughter strand called in DNA replication

Lagging strand

What condition can DNA polymerase only ADD nucleotides to?

a growing polymer

What is made when the replication fork moves along the lagging strand?

RNA primer is made

When DNA polymerase I removes the RNA primer, what is it replaced with?

DNA

Why do cells stop replicating linked to a limit?

The Hayflick Limit - an upper limit of how many times a normal human cell (not a stem cell) can divide before it can no longer divide

Why do cells stop replicating to do with telomere?

•Telomere - a region of repetitive DNA sequences at the end of a chromosome.

•Telomeres protect the ends of chromosomes from becoming frayed or tangled with a 'T-Loop'

•Each time a cell divides, the telomeres become slightly shorter.

•As cells cycle they loose a bit of the end of their chromosomes

What do the spindle fires do in the mitotic spindle?

polymerisation of tubulin molecules to form microtubules originating at the centrioles.

•Kinetochore fibers extend from the pole of the spindle to the centromere of the chromosome to which they attach

In meiosis what is the formation of haploid gametes?

•Preceded by interphase which includes chromosome replication

•Two meiotic divisions - Meiosis I and Meiosis II

•A reductive division

•Original cell is diploid

•Four daughter cells produced that are 'monoploid' or haploid

How is a synapsis formed?

Two homologous chromosomes join to form a tetrad

What are the stages of meiosis I?

Interpjase I, Prophase I, Metaphase I, anaphase I

What happens in interphase I ?

chromosomes duplicate

what happens in prophase I?

The chromosomes condense, and the nuclear envelope breaks down. crossing-over occurs.

What happens in metaphase I?

Tetrads line up at spindle equator

What happens in anaphase I?

Homologous chromosomes separate

What happens in meiosis II?

cells go from being diploid to haploid

What are the three mechanisms that contribute to chromosomal genetic variation?

1)Independent assortment of chromosomes

2)Crossing over

3)Random fertilization

What does the term aneuploidy mean in the sense of genetic variation?

Any deviation from the normal number of chromosomes, usually meaning a cell nucleus possessing too many or too few chromosomes.

What three names are given when something goes wrong in meiosis?

-Trisomy

-Monosomy

-Tetrasomy

What causes Downs Syndrome?

•Nondisjunction of the 21st chromosome - Trisomy 21

What does Downs Syndrome result in?

Results in characteristic facial and body patterns, varying mental abilities.

What is Patau syndrome caused by?

trisomy of chromosome 13

What facial defects is caused by Patau syndrome?

-microphthalmia

-absent or malformed nose

-cleft lip and/or cleft palate

What neurological problems is caused by Patau syndrome?

-Microcephaly

-Severe mental deficiency

What is Edwards' syndrome affected by?

Trisomy 18

What does Edwards' syndrome cause?

-Low birth weight

-Prominent occiput

-Clubbed hands

What Neurological problems is caused by Edwards' Syndrome?

Severe development delays

What facial defects is caused by Edwards' syndrome?

-Small mouth and chin

-Low set and malformed ears

-cleft lip and/or cleft palate

What is Klinefelter's syndrome caused by?

•Nondisjunction of the X Chromosome

What is the result from Klinefelter's syndrome?

Results in sterile males with female characteristics

What is Turner syndrome?

•Nondisjunction of the X

• Sterile females with webbed necks,

shortened torso

How many chromosomes does a person with Turner syndrome have, and what are they?

45 chromosomes - XO not XX