MCAT Kaplan Biology Chapter 2: Reproduction

Four stages of Cell Cycle

G1, S, G2, M

What stages are involved in the INTERPHASE

G1, S, G2

what is the longest part of the cell cycle?

Interphase

What is G0

cell is simply living and serving its function, not prepping for division

What part of the cell can you NOT see during interphase and why

Chromosomes because they are in a less condensed form called chromatin so that the DNA can be available for transcription via RNA polymerase

During mitosis, what happens to the DNA and why

it becomes very condensed and tightly coiled as to not lose any genetic material during cell division

Describe G1 Stage

organelle creation for energy and protein production and increase in size, Dna examined and repaired

Resitriction point or the G1/S checkpoint

After G1 stage, when the cell becomes "committed" to the cell cycle and after which extracellular proliferation stimulants are no longer required.

cell checks to see if DNA is good enough to replicate/cell cycle will arrest if DNA damage needs repairing (controlled by P53)

Describe S stage

1)replication of genetic material

2)sister chromatids are bound at the centromere

G2 stage

cell goes through quality control checkpoint where cell checks to make sure that there are enough organelles and cyto to divide into two cells. DNA is checked for errors

M stage

mitosis+cytokinesis

P53 importance in restriction point

involved in checking for errors in DNA before entering the S phase so that dna damage is fixed.

G2/M checkpoint

cell checks to see if cell is adequately sized to split in two, has enough organelles, p53 also involved here

Which two molecules are responsible for the cell cycle progression and how do they work

cyclins and clyclin dependent kinases. Presence of certain cyclins at certain points activate appropriate CDKs and create a camplex that then phosphorylates transcription factors for the genes required in the next stage of the cell cycle

What happens when p53 is mutated in cancer

it can no longer stpo cell cycle to repair DNA damage allowing more mutations to accumulate

Four stages of mitosis

prophase, metaphase, anaphase and telophase

mitosis happens in what kind of cells

SOMATIC NOT GERM CELLS

Prophase

first stage of mitosis

1)condesnation of chromosomes

2)centriole pairs move towards opp poles to create spindle fibers in preparation to divide DNA

3) Nuclear membrane dissolves to allow spindle fibers to contact the chromos

4) nucleoli begins to disappear

5)kinetochores appear at the centromeres of chromosomes

What happens to the centrioles during prophase

they move towards opp poles and create spindle fibers that emanate from the centrosomes. Some reach towards center, other, called asters anchor the centrioles to the cell membrane

asters

the microtubules emanating from centrosomes during prophase that anchor the centrioles to the cell membrane

function of kinetochore fibers during prophase

they appear at the centromere and are protein structures that serve as attachment points for specific fibers in the spindle apparatus TO the chromatids. Their proteins help to hold the sister chromatids together

Metaphase

centriole pairs are now at opp ends, kinetichore fibers interact with spindle to align chromosomes at the METAPHASE PLATE (equidistant between the two poles)

Anaphase

centromeres split so that each chromatid has its own centromere, allowing their separation

How are sister chromatids pulled apart?

by the shortening of kinetochore fibers

Telophase

Spindle disappears, nuclear membrane reforms around the two sets of chromosomes, nucleoli reappears, chromosomes uncoil/decondense

then cytokinesis

cytokinesis

separation of cyto and organelles via cleavage furrow

Meiosis

cell division for gametocytes, resulting in up to four nonidentical gametes

What are the similarities between meiosis and mitosis

in both, dna is duplicated, chromatin condensed and microtubules emanating from centrioles are involved in dividing genetic material

what are the differences between meiosis and mitosiss

meiosis consists of one round of replication followed by TWO rounds of division, whereas mitosis only has ONE round of division

meiosis I results in

homologous chromosomes being separated, generating haploid daughter cells

meiosis II

similar to mitosis in that it results in separation of sister chromatids

reductional division

process of meiosis I

equational division

process of meioosis II

Prophase I

chromatin condenses into chromosomes

spindle forms

nucleoli and nuclear membrane disappear

HOMOLOGOUS RECOMBO

Synapsis

intertwining of chromosomes during prophase 1

tetrad

the complex of four chromatids during synapsis

Chiasma

tetrad undergoing homologous recombo

Mendel's second law of independent assortment

inhertiance of one allele has no effect on the liklihood of inherting certain alleles for other genes, explained by homologous recombo that allows different recombination of alleles from different (homologous) chromosomes

Metaphase 1

tetrads align at metaphase plate and each pair attaches to a separate spinle fiber at the kinetochore

Anaphase 1

homologous pairs of chromosomes are separated and pulled to opp poles of cells

Disjunction

separation of homologous pairs during Anaphase 1

Telophase 1

nuclear membrane forms around new nuclei, CELLS ARE HAPLOID, cell divides via cytokinesis

interkinesis

short rest period between first cell division of meiosis and second, chromosomes partially uncoil

Meiosis II

similar to mitosis where sister chromatids are separated (rather than homologous chromosomes)

Prophase II

nuclear envelope dissolves, nucleoli disappear, centrioles migrate to opp poles, spindle forms

metaphase II

chromosomes line at metaphase plate

Anaphase II

centromeres divide and separates the sister chromatids, chromatids pulled to opp poles via spindle fibers

Telophase II,

nuclear membrane forms, cytokinesis separates two daughter cells, four haploid daughter cells produced.

difference between mitosis and meiosis: Prophase I

homologous chromosomes form tetrads and start crossing over

difference between mitosis and meiosis: Metaphase I

homologous chromosoles line up on opposite sides of the metaphase plate, instead of individually

difference between mitosis and meiosis: Anaphase I

homolougous chromosomes separate, centromeres remain intact

difference between mitosis and meiosis: Telphase I

chromatin may or may not decondense, interkinesis occurs as cell prepares for meiosis II

hemizygous

designated for males because they only have one copy of X

females on the other hand can be homozygous or heterozygous

Most X-linked disorders are dom or recessive

what is the effect on males and females

recessive, females less likely to display the disease because they need to X's for it to be expressed. Males are hemizygous and therefore suffer from these disorders more often

SRY

notable gene on Y chromosomes hich codes for transcription factor that initiates testis differentiation and formation of male gonads

functional componants of testes and their function

seminiferous tubules-produce sperm via spermatogensesis

interstitial cells of Leydig-testosterone/androgen secretion

Sertoli cells- nourish sperm

Maintenance of sperm temperature

via layer of muscle around vas deferens that can lift or lower testes to maintain proper temperature of sperm

epididymis

where sperms flagella gain motility and are stored until ejaculation

process of ejaculation

sperm travel from epididymis through vas deferens to the ejaculatory duct which fuses from both sides to become the urethra

seminal fluid

produced by seminal vesicles (fructose component to nourish sperms), prostate gland (gives sperm alkiline properties so sperm can survive in the acid female reproductive tract) and bulbourethral/Corpus gland (produces clear viscous fluid to clean out remannts of urine and lubricates urethra during sexual arousal

semen

sperm+seminal fluid

spermatogensis stages

1) spermatogonia (diploid cells)

2)primary spermatocytes (post S phase duplication)

3)secondary spermatocytes (After miosis I, haploids)

4)spermatids-post miosis II, haploids)

5)spermatozoa-post maturation

Parts of mature sperm

Head- nucleus and acrosome (derived from golgi and used to penetrate ovum)

midpiece- lots of mitochondria to generate energy from fructose

flagellum- for motility

ovaries

female gonads, produce estrogen and progesterone

and ova production

follicles

multilayered sacs that make up the ovary which contain nourish and protect ovas

ovulation

ova travel through peritoneal sac (lines abdominal cavity) and drawn into fallopian tube, which is lined with cilia to propel egg to the uterus

cervix

lower end of uterus that connects to vaginal canal, where sperm is deposited

oogenesis

1) by birth, oogonia already undergone DNA replication to form primary oocytes (2n), and are arrested in prophase I, one primary oocyte PER MONTH undergoes the rest of meiosis

2) after meiosis 1, ONE secondary oocyte and ONE polar body is formed; accamplished through UNEQUAL cytokinesis, giving lots of cyto to ONE and hardly any to the other

3) polar body does not divide again, secondary oocyte remains in metaphase II UNTIL fertilization occurs

difference between oogenesis and spermatogensis

NO nending supply of stem cells in females, all of oogonia women will have is formed during fetal development

spermatogensis produces four sperm, oogensis normally produces ONE egg

zona pelucida

surrounds the oocyte, acellular mixture of glycoproteins that protect oocyte and can bind to sperm

corona radiata

outside zona pellucida, layer of cells that adhere to oocyte during ovulation

Fertilization

acrosomal enzymes of sperm penetrate the corona radiata and initiates secondary oocyte into meiosis II, producing mature ovum and one polar body,

after meiosis II completion, sperm and ovum join to create zygote

Hormones in sexual development

hypothalamus restricts production of GnRH until puberty

pulses of GnRH triggers anterior ppituitary glad to release FSH and LH

these hormones trigger production of sex hormones that develope and maintain repro system

male sex dev

Y chromosome allows for androgen production, resulting in male differentiation

Androgen production low during infancy/childhood

Puberty accomplished via testosterone

FSH stimulates Sertoli cells for sperm maturation

LH causes interstitial cells to produce testosterone

testosterone exerts negative feedback on hypo and anterior pituitary to limit its own production to appropriate levels

What does FSH stimulate in males during puberty

Sertoli cells for sperm maturation

What does LH stimulate in males during puberty

interstitial cells to produce testosterone

secondary sexual characteristics of males

facial/pube hair, deep voice, growth

Female sex dev

FSH causes esetrogen secretion which develops/maintains female repro system and female secondary sexual characteristics

Estrogen also leads to thickening of lining in uterus (endometrium) each month to prepare for fertilization

LH stimulates corpus luteum to produce progesterone which is involved in the maintenance and development of the endometrium.

female secondary characteristics

breast, hip widening, fat distribution

endometrium

lining of uterus

What does FSH stimulate in females during puberty

estrogen secretion for maintenance/development of repro system, also for thickening endometrium in preparation for fertilization

facilitates maturation of single ovum

What does LH stimulate in females during puberty

corpus luteum to produce progesterone which develops and maintains the endometrium

Four phrases of menstrual cycle

follicular, ovulation, luteal, menstruation

Follicular phase of menstrual cycle

1)menstrual flow begins

2)low estrogen and progesterone

3)high GnRH

4)secretion of GnRH stimulates a little bit of FSH and LH which works to develop ovarian follicles

5)ovarian follicles produce estrogen which has a negative feedback on GnRH and levels off FSH and LH production

6)After menstrual flow ends, estrogen works to regrow endometrial lining

7) egg develops

LOW FSH, LOW LH, LOW ESTROGEN, THEN ESTROGEN SPIKE, LOW PROGESTERONE

Ovulation

ovarian follicles produce more and more estrogen. At high enough concentrations it has a POSITIVE feedback loop on GnRH, LH and FSH levels which then spike

LH induces ovulation, egg releases

HIGH FSH, HIGH LH, HIGHER ESTROGEN, low progesterone

Luteal Phase

After ovulation, LH makes ovarian folliles form into corpus luteum which then produces progesterone

Progesterone rises causing negative feedback on GnRH, FSH and LH to prevent multiple eggs

LOW FSH, Lower LH, HIGH ESTROGEN, HIGH PROGESTERONE

Menstruation

Corpus luteum loses stimulation from LH, progesterone declines, uterine lining is therefore not maintained and is shed, low estrogen and progesterone ultimately leads to GnRH to increase and repeat the cycle

LOW FSH; LH; ESTROGEN; PROGESTERONE

Pregnancy process

zygote-->blastocyst--> implants into uterine lining

blastocyst produces hCG (LH analog) that maintains the corpus luteum and continues estrogen and progesterone production

estrogen/progesterone important in first trimester to keep uterine lining in place

Second trimester, hCG declines because placenta grows and secretes estrogen and progesterone by itself

Menopause process

ovaries less sensitive to FSH and LH, causing ovarian atrophy. estrogen and progesterone levels drop and endometrium atrophies and menstruation stops.

FSH, LH levels rise in blood because no neg feedback loop from estrogen and progesterone