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mcat biology > Reproduction > Flashcards

Reproduction Flashcards

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0
Q

the cell cycle: interphase

A
  • the longest part of the cell cycle
  • G1 (presynthetic gap) cells create organelles for energy and protein production (mito, ribo, endo ret) while also doubling in size; plus passage into the s phase governed by a restriction point -> certain criteria must be metfor the cell to pass the restriction point and enter the sunthesis phase
  • S Stage (synthesis) cell replicates (synthesizes) its genetic material so that each daughter cell have identical copies; after replication each chromosome has 2 identical chromatids, which are bound together at a specialized region known as centromere
  • G2 stage (post synthetic gap) final stage before division; like quality control - making sure that we have enough organelles and cytoplasm to make 2 daughter cells
  • chromosomes not visible with light microscopy -> in a less condensed form known as chromatin -> dna must be open so can transcribe genes and replicate organelles before division
  • mvmt of chromosomes depends on centrioles: paired cylindrical organelles, located outside the nucleus in a region known as centrosome, responsible for correct division of DNA –> during prohase centrioles move opposite poles and form spindle fibers (made of microtubules) which radiate out from centrioles and have attachment points known as asters (extend toward center of the cell to form spindle apparatus and subsequent shortening of this apparatus results in separation of sister chromatids)
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1
Q

cell division

A

-for prokaryotes (all unicellular) cell division provides mechanism of reproduction, same goes for unicellular eukaryotes
-for eukaryotes multicellular, cell division also replaces cells that are ready to retire
-prokaryotes divide via binary fission, asexual reproduction, single dna molecule replicates itself while cell grows and then membrane invaginates
- eukaryotic cells have multiple chromosomes per cell , need new cytoplasm and organelles
-eukaryotic autosomal cells have the diploid (2n) number of chromosomes while haploid, r germ cells, have the n number of chromosomes
~~ diploid = 46, haploid = 23 chromosomes -> we inherit 23 chromosomes from each parent

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2
Q

the cell cycle: mitosis (m stage)

A
  • mitosis is divided into 4 phases: prophase, metaphase, anaphase, telophase
  • Prophase: chromosomes condense, centrioles pairs move toward opposite poles of the cell, spindle apparatus forms between them; nuc membrane dissolves, spindle fibers enter nucleus; kinetochores, appear at the chromosome centromere
  • metaphase: kinetochore fibers interact with fibers of the spindle apparatus to align chromosomes at the metaphase plate (equidistant from two poles of spindle)
  • anaphase: centrioles split so each chromatid has own centromere , sisters separate and pulled to opposite poles of cell by shortening kinetochore fibers
  • telophase and cytokinesis: spindle disappears, nuc membrane refors around each set of chromosomes, chromosomes uncoil and resume interphase form; cytokinesis (splitting of cell in half) occurs
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3
Q

binary fission

A
  • simple form of reproduction seen in prokaryotes
  • circular chromosome ataches to the cell wall and replicates while the cell continues to grow insize
  • plasma membrane and cell wall start to grow inward along midline of cell to make 2 equal daughter cells
  • can proceed rapidly
  • NOT genetically diverse in asexual reproduction
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4
Q

budding

A
  • equal replication followed by unequal cytokinesis
  • daughter cell receives dna identical to parents but far less cytoplasm -> may immediately break off
  • results in cells of unequal size unlike binary fission
  • can occur in eukaryotes
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5
Q

regeneration

A
  • an entire body part can be regrown
  • primarily occurs in lower organisms and is accomplished by mitosis
  • high organisms have more difficulty with this process primarily due to nerve damage because CNS nerves do not regenerate
  • however livers can regenerate
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6
Q

parthenogenesis

A
  • process where adult organism develops from an unfertilized egg
  • social insects produce males via this
  • does not occur naturally in higher organisms, but has been induced in lab rabbits
  • however the daughter cell will be haploid in number because only one parent contributed genetic material
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7
Q

meiosis 1 - prophase 1

A
  • meiosis composed by one round of replication followed by two rounds of division
  • meiosis 1 (first division) results in homologous chromosomes being separated, generating haploid daughter cells (reductional division)

-Prophase 1: homologous chromosomes code for same genes and one is inherited from each parent; during prophase the chromatin condenses into chromosomes, spindle apparatus forms, nucleoi and nuclear membrane disappear
— diff from mitosis = homologous chromosomes come together and intertwine in a process known as synapsis
~~>each chromosome consists of 2 sister chromatids, so each SYNAPTIC PAIR of homologous chromosomes contains four chromatids (2 sets of sisters); chromatids of homologous chromosomes may break at the point of synapsis (chiasma, plural = chiasmata) and exchange equivalent pieces of dna —> called CROSSING OVER

crossing over occurs between homologous chromosomes (2 different sets of sister chromatids) and not between sister chromatids of the same chromosome (which are identical anyways) – and then chromatids involved are left with an altered by structurally complete set of genes and sister chromatics(which are connected) are no longer identical

crossing over increases the variety of genetic combinations that can be produced via gametogenesis

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8
Q

Meiosis - Metaphase 1

A
  • homologous pairs (the two pair of sister chromatids) align at the metaphase plate and each pair attaches to a separate spindle fiber by its kinetochore
  • chromosomes are all neatly lined up on the metaphase plate
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9
Q

Meiosis - anaphase 1

A
  • homologous pairs separate and are pulled to opposite poles of the cell (called disjunction)
  • -> each chromosome of paternal origin separates from its pair of maternal origin, and either chromosome can end up in either daughter cell
  • the distribution of homologous to the two immediate daughter cells is random with respect to parental origin
  • each daughter cell will have a unique pool of alleles from a random mix of maternal and paternal origin
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10
Q

meiosis - telophase 1

A
  • a nuc membrane forms around each new nucleus
  • each chromosome still consists of sister chromatids joined at the centromere
  • haploid in each cell at this point - once homologous chromosomes separate only the n number of chromosomes is left (23) BUT still 46 chromatids (2 per chromosome)
  • cell divides by cytokinesis into 2 daughter cells
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11
Q

mitosis vs meiosis

A

mitosis:

  • 2n->2n
  • occurs in all dividing cells
  • homologous chromosomes DONT pair
  • no crossing over
  • PMAT CASN

Meiosis:

  • 2n -> n
  • occurs in sex cells only
  • homologous chromosomes pair up at metaphase plate forming TETRADS
  • crossing over can occur
  • occurs twice so has 4 daughter cells
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12
Q

Meiosis 2 - prophase 2

A
  • very similar to mitosis
  • not precedented by chromosomal replication
  • the centrioles migrate to opposite poles and the spindle apparatus forms
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13
Q

meiosis 2 - metaphase 2

A
  • the chromosomes line up along the metaphase plate (sister chromatids which is a single chromosome NOT homologous chromosomes)
  • centromeres divide separating the chromosome into a pair of sister chromatids per daughter cell
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14
Q

Meiosis 2 - anaphase 2

A

-sister chromatids are pulled to opposite poles by the spindle fibers

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15
Q

Meiosis 2 - Telophase 2

A
  • nuclear membrane forms around each new (haploid) nucleus
  • cytokinesis follows and two daughter cells are formed
  • by the end, four haploid daughter cells are produced PER gametocyte –> in females only one of these becomes a functional gamete
  • random distribution of chromosomes in meiosis plus coupled with crossing over = produce gametes with many different genetic combinations
  • -> sexual reproduction provides advantage of great genetic variability which increases capability of a species to evolve and adapt to a changing environment
16
Q

male reproductive anatomy (sevenup)

A

-gonads develop to testes
-testes have 2 functional components: seminiferous tubules and interstitial cells
–> sperm produced in seminiferous tubules, where nourished by Sertoli cells and cells of Leydig secrete testosterone and other male androgens
- testes located in scrotum which hangs below penis and is 2-4 degrees celcius lower than the rest of the body because enymes function only at that temp
-as sperm mature passed to epididymis, have flagellum, and stored there until ejaculation –> travel through ejaculatory duct and urethra and exit through the penis (reproductive and urinary systems share common pathway)
- as sperm pass through reproductive tract, mixed with seminal fluid, which made by joint effort by seminal vesicles, prostate gland, and bulbourethral gland — this combination of sperm and fluid is known as semen
~~seminal vesicles give fructose to nourish sperm where prostate gland gives fluid alkaline properties so can survive acidity of female reproductive tract

17
Q

spermatogenesis

A
  • form haploid sperm through meiosis
  • occurs in seminiferous tubules
  • diploid stem cells known as spermatogonia; via differentiation, replicate genetic material and dev to diploid primary spermatocytes
  • first meiotic division result in haploid secondary spermatocytes which then do meiosis 2 to generate haploid spermatids which then mature to become spermatozoa

spermatogonia (2n) -> primary spermatocytes (2n) -> meiosis 1 -> secondary spermatocytes (n) -> meiosis 2 -> spermatids (n) -> spermatozoa (n)

-spermatogenesis creates 4 functional sperm for each spermatogonium

mature sperm: head with genetic material, midpiece (to make energy from fructose for motility) and flagellum (motility) —> make atp, mitochondria must be abundant in midpiece
–> each sperm head covered by cap known as acrosome, necessary to penetrate ovum

18
Q

female reproductive anatomy

A
  • gonads, ovaries, make estrogen and progesterone
  • ovaries below digestive system and each has thousands of follicles (multilayered sacs that contain, nourish, and protect immature ova)
  • one egg/month released into peritoneal sac, lines abdominal cavity, moves into Fallopian tube (oviduct) (lined with cilia move it along), fallopian tube connected to uterus (site of fetal dev)
  • lower end of uterus (cervix) connects to vaginal canal (where sperm deposited)
  • external female anatomy known as vulva
19
Q

oogenesis

A
  • aka the production of female gametes
  • no unending supply of stem cells analogous to spermatogonia –> all the oogonia a woman will ever have are formed during fetal development
  • at birth, pre differentiated cells known as primary oocytes -> 2n and frozen in prophase 1; once woman reaches menarche, one primary oocyte per month will complete meiosis 1 -> secondary oocyte and a polar body
  • –>division unequal cytokinesis gives cytoplasm to oocyte and not any to the polar body which then the polar body doesnt divide or makes functional gametes while the secondary oocyte remains frozen in metaphase 2 and does not complete the remainder of meiosis 2 unless fertilization occurs
  • 2 cell layers surround oocytes: zoona pellcida and corona radiata
  • meiosis 2 triggered when sperm penetrates these layers with help of acrosomal enzymes, secondary ocytes then undergo second division to split into a mature ovum and another polar body
  • a mature ovum is very large cell consisting of large amounts of cytoplasm and organelles

primary oocyte (n) -> meiosis 1 -> secondary oocyte (n) -> fertilization ->meiosis 2 -> ovum (n)

until menopause, women ovulate once secondary oocyte every 28 days, after menopause the ovaries less sensitive to stimulating hormones (FSH) and luteinizing hormone (LH) and eventually the ovaries atrophy — since ovaries don’t respond, these hormone levels skyrocket which results in physical and physiological changes

-key: spermatogenesis in males results in 1 spermatogonia to 4 equal and viable spermatozoa while in females oogenesis results in 1 ovum from 1 oocyte

20
Q

fertilization

A
  • secondary oocytes can be fertilized within 24 hours of ovulation
  • sperm survive for 1-2 days after ejaculation if the uterine is suitable
  • fusion of these haploid cells, in widest part of Fallopian tubes, results in restoration of diploid chromosome number and a cell known as zygote
  • once first sperm comes into direct contact with 2 oocyte cell membrane, forms tubelike structure known as acrosomal apparatus (extends to and penetrates cell membrane) and nuc may freely enter ovum
  • after this, ovum undergoes cortical reaction where ca2+ ions released into cytoplasm and leads to formation of fertilization membrane which is impermeable to other sperm
21
Q

monozygotic twins

A
  • develop when a single zygote splits into two
  • identical twins
  • genetic material all the same
  • if incomplete division, conjoined twins may result
  • share same genome and blood type
22
Q

dizygotic twins

A
  • if two eggs are released in the same cycle they may both be fertilized
  • each zygote will implant in the uterine wall individually and develop separately
  • fraternal twins
  • no more genetically similar than any other pair of siblings

mcat biology (9 decks)

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