Kaplan MCAT Biology 04

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Kaplan MCAT Biology 04

Acrosome

- cap-like structure, over the anterior half of mature sperm's head
- derived from Golgi apparatus
- contains enzymes to penetrate the tough outer covering of the ovum
- once in contact with ovum cell membrane, sperm forms a tubelike structure called the acrosomal process
- acrosomal process extends and fuses with ovum and enters the ovum's cytoplasm

Anaphase

- sister chromatids separate
- telomeres are the last part of the chromatids to separate

Anaphase I

- disjunction: homologous pairs separate and are pulled to opposite poles of the cell
- distribution of homologous chromosomes to intermediate daughter cells are random

Anaphase II

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

Asexual Reproduction

- essentially genetic carbon copies of parent cells
- identical to parent cells except for random mutations
- different types: binary fission, budding, regeneration, parthenogenesis

Binary Fission

- prokaryotes' way of of cell division
- a type of asexual reproduction
- splits into two equal halves, each daughter cell receives a complete copy of the original chromosome

Binary Fission

- a simple form of asexual reproduction in prokaryotes
- circular chromosome replicates
- a new plasma membrane and cell wall grow inward along the midline of the cell, dividing it into two
- each daughter cell contains a duplicate of the parent chromosome

Budding

- replication of the nucleus followed by unequal cytokinesis
- the cell membrane pinches inward to form a new cell that is smaller in size but genetically identical to the parent cell
- can grow to an adult size
- new cell may separate immediately from the parent or remain attached to it
- occurs in hydra and yeast

The Cell Cycle

- four stages: G₁, S, G₂ and M
- interphase: first three stages
- mitosis includes the actual cell division

Cell Division

- a process where a cell doubles its organelles and cytoplasm, replicates its DNA and then divides in two
- unicellular organism: reproduction
- multicellular organism: growth, development & replace old cells

Cervix

- lower, narrow end of the uterus
- connects with the vaginal canal

Chiasmata

where chromosomes are joined

Chromatin

- granular DNA during interphase

Chromosome Movement

- dependent on these cytoplasmic organelles
- centrioles: found in pairs, cylindrical organelles
- centrosome: an area outside the interphase nucleus
- spindle fibers: composed of microtubules, appears near each pair of centrioles, radiate outward.
- asters: spidle fibers in radiating structure
- spindle apparatus: asters extending toward the center of the nucleus, shortens to move chromosomes toward
opposite poles of the cell during the later stages of mitosis

Corona Radiata

- outer layer of the oocyte cell membrane

Cortical Reaction

- triggered by acrosomal reaction
- calcium ions released into the cytoplasm, initates a series of reaction to form the fertilization membrane
- calcium ion also stimulates increase in ovum's metabolic rate
- this is followed by fusion of the sperm nucleus with ovum nucleus to form a diploid zygote

Cytokinesis

- happens at the end of telophase
- cytoplasm divides into two daughter cells
- in animal cells, a cleavage furrow forms, cell membrane indents along the equator of the cell and cell split

Dizygotic (fraternal) Twin

- results when two ova are released in one ovarian cycle
- fertilized by two different sperm
- two embryos implant in the uterine wall individually
- each develops its own placenta, amnion and chorion
- share characteristics in the level of siblings

Epididymus

where sperm acquire motility and stored here till ejaculation

Female Reproductive Anatomy

- once a month, an immature ovum is released from the ovary into the abdominal cavity and drawn into the nearby fallopian tube
- inner surface of the fallopian tube is lined with cilia that move the ovum into and along the tube and toward the uterus
- mammalian female's reproductive and excretory systems are distinct from one another (urethra and vagina aren't connected)

Fertilization

- happened 12-24 hours after ovulation
- occurs in the lateral, widest portion of the fallopian tube
- sperm travels through vaginal canal, cervix, uterus, and into the fallopian tubes to reach the ovum
- sperm penetrates corona radiata, then zona pellucida, contact with ovum cell membrane, become acrosomal process, fuse sperm with ovum
- sperm nucleus enters ovum's cytoplasm and ovum completes meiosis II

Fertilization Membrane

- hard layer that surrounds the ovum cell membrane
- prevents multiple fertilizations

Follicles

- multilayered sac of cells that contains, nourishes and protects and immature ovum
- follicle cells produce estrogen

G₁ Stage (presynthetic gap)

- intense biochemical activity and growth
- cell doubles in size and new organelles are produced
- passing "restriction point", where a cell is committed to continue through the rest of the cell cycle and divide
- some cells like skeletal muscle cells and nerve cells never pass this point, and enter a nondividng phase sometimes referred to as G₀
- 2N number of chromosomes

G₂ Stage (postsynthetic gap)

- cell continues to grow in size
- assembly of new organelles and other cell structures continues

Gametes

- sperm and egg
- produced in gonads

Gonads

- male: testes
- female: ovaries

Homologous Chromosomes

chromosomes that code for the same trait, one inherited from each parent

Interphase

- the longest part of the cell cycle
- a cell normally spends at least 90% of the cycle in interphase

M Stage (Mitosis)

- mitosis: division and distribution of the cell's DNA to its two daughter cells such that each cell receives a complete copy of the original genome
- cytokinesis: division of cytoplasm that follows
- happens on somatic cells only
- 2N --> 2N (ends up with two diploid cells)

Male Reproductive Anatomy

- testes contain two functional components: seminiferous tubules and interstitial cells (cells of Leydig)
- sperm are produced in seminiferous tubules, nourished by Sertoli cells
- interstitial cells secrete testosterone and anderogens
- testes have to be 2-4°C lower than body temperature

Meiosis

- only occurs in the sex cells
- meiosis I produces two intermediate daughter cells
- meiosis II is similar to mitosis, it separates sister chromatids and results in four genetically distinct haploid gametes

Meiosis II

- doesn't occur until fertilization
- triggered when zona pellucida and corona radiata are penetrated by a sperm cell
- fertilization yields two haploid cells, a mature ovum and another polar body
- the mature ovum is a large cell containing a lot of cytoplasm, RNA, organelles and nutrients needed by a developing embryo

Meiosis II

- similar to mitosis
- not preceded by chromosomal replication

Menarche

- the first time a female gets her period

Metaphase

- chromosomes align

Metaphase I

- homolgous pairs (tetrads) align at the equatorial plane
- each pair attaches to a separate spindle fiber by its kinetochore

Metaphase II

- chromosomes line up along the equatorial plane
- centromeres divide
- chromosomes separate into pairs of sister chromatids

Monozygotic (identical) Twins

- result when a single zygote splits into two embryos
- if splitting occurs at the two-cell stage of development, embryos will have separate chorions and separate placentas
- if it occurs at blastula stage, embryos only have one chorionic sac and share a placenta (and probably amnion)

Oogenesis

- production of female gametes
- occurs in the ovarian follicles
- one primary oocyte completes meiosis I per month after menarche
- yields two secondary oocyte and a polar body
- secondary oocyte is expelled from the follicle during ovulation
- meiosis II doesn't occur till fertilization

Ovaries

- female gonads
- found in the abdominal cavity
- produce eggs (ova)
- secrete esterogen and progesterone
- consist of thousands of follicles

Ovulation and Menopause

- women ovulate about once every four weeks
- menapause occurs between age 45 and 50
- during menopause, ovaries become less sensitive to the hormones that stimulate follicle development (FSH and LH), and eventually they atrophy
- remaining follicles disappear, estrogen and progesterone levels greatly decline and ovulation stops

Parthenogenesis

- development of an unfertilized egg into an adult organism
- occurs naturally in certain lower organisms (bees and ants, some salamander)
- eggs of some organisms can be induced to develop parthenogenetically (not done naturally)
- since the organism develops from a haploid cell, all of its cells will be haploid

Pathway of Sperm

SEVEN UP:
Seminiferous tubules
Epididymus
Vas deferens
Ejaculatory duct
(Nothing)
Urethra
Penis

Primary Oocyte

- immature ova
- diploid cells that form by mitosis in the ovary
- at birth, all of the primary oocyte that a female will produce during her lifetime are already in her ovaries

Prophase

- chromosomes condense
- centriole pairs separate and move toward opposite poles of cell
- spindle apparatus form
- nuclear membrane dissolves
- kinetochores, attached kinetochore fibers, appear at the chromosome centromere

Prophase I

- homologous chromosomes come together and intertwine
- at this stage, chromosome consists of two sister chromatids
- where recombination and crossing over happens, responsible for increased genetic diversity

Prophase II

- centrioles migrate to opposite poles
- spindle apparatus forms

Regeneration

- the regrowth of a lost or injured body part
- replacement of cells occurs by mitosis
- ex: hydra and starfish
- in higher animals, regeneration is usually limited to the healing of tissues
- some internal organs (liver) can regenerate considerably as long as part of the organ remains viable

Reproduction

- a process by which an organism perpetuates itself and its species
- divided into: cell division, asexual reproduction and sexual reproduction

S Stage (synthesis)

- each chromosome is replicated so that during division, a complete copy can be distributed to each daughter cell
- two identical sister chromatids held together at a region called the "centromere"
- telomeres: ends of the chromosomes
- 2 x 2N number of chromosomes

Seminal Fluid

- mixed with sperm, aids in sperm transport by lubricating passageways
- semen: sperm + seminal fluid
- produced by:
a) seminal vesicles: fructose-rich fluid, serves as energy source
b) prostate gland: alkaline milky fluid to protect from acidic environment in female's reproductive tract
c) bulbourethral glands: small amount of viscous fluid, function unknown

Sexual Reproduction

- fusion of two gametes (specialized sex cells produced by each parent)
- meiosis is the process where the sex cells are produced
- mitosis preserves the diploid chromosome number while meiosis halves it
- somatic cells undergo mitosis, gametocytes undergo meiosis
- during fertilization, two haploid gametes fuse, restoring the diploid number

Somatic Cells

- or called autosomal cells
- everything but the gamete
- contain diploid number of chromosomes characteristic of its species (2N)
- N is the number of chromosomes found in haploid cell (gamete)
- in human, 2N = 46 and N = 23

Spermatogenesis

- "sperm production"
- occurs in seminiferous tubules
- after a male reaches sexual maturity, about 3 million primary spermatocytes begin spermatogenesis per day
- maturation takes about 65-75 days

Spermatogenesis Process

- spermatogonia (diploid) differentiate into primary spermatocytes (diploid)
- primary spermatocytes undergo the first meiotic division and yield two secondary spermatocytes (haploid)
- secondary spermatocytes undergo second meiotic division and yield four spermatids (haploid)
- spermatogonia (2N) --> 1° spermatocytes (2N) --> meiosis I --> 2° spermatocytes (N) --> spermatids (N) --> spermatozoa (N)

Spermatozoa

- spermatids after a series of changes, becomes a mature sperm
- mature sperm is an elongated cell with a head, neck, body and tail
- head consists almost entirely of the nucleus
- tail (flagellum) propels the sperm
- mitochondria in the neck and body provide energy for locomotion

Stages of Mitosis

PMAT:
a) Prophase
b) Metaphase
c) Anaphase
d) Telophase

Synapsis

homologous chromosomes come together and intertwine

Telophase

- spindle apparatus disappears
- new nuclear membrane forms around each set of chromosomes
- nucleoli reappears
- chromosomes uncoil
- cytokinesis occurs

Telophase I

- a nuclear membrane forms around each new nucleus
- each chromosomes still consists of sister chromatids joined at the centromere
- cells divide into two daughter cells
- between cell divisions, there might be "interkinesis", a short rest period where chromosomes partically uncoil

Telophase II

- nuclear membrane forms around each new haploid nucleus
- two daughter cells are formed after cytokinesis
- by completion of meiosis II, four haploid daughter cells are produced per gametocyte

Tetrad

chromosome consisting of two sister chromatids

Uterus

- site of fetal development

Vaginal Canal

- site of sperm deposition during intercourse
- passageway through which a baby is expelled during childbirth

Vulva

- external female genitalia

Zona Pellucida

- inner layer of the oocyte cell membrane

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