Ch 2 - Reproduction

Question 1

cell cycle

Answer 1

• interphase - G1, S, G2
  
  • dividing cells spend about 90% of time in this stage
  • G_o is a part of G₁ where the cell is not living and not preparing for division
• during interphase chromosomes are in less condensed form - chromatin
  
  • not visible under light microscopy
• during mitosis the chromosomes are condensed so they divide easily

Question 2

G₁ - presynthetic gap

Answer 2

• create organelles
  
  • proteina and energy prodcution
• increase size
• pass restriction point to move to S phase
  
  • is DNA good enough for synthesis
  • will go into arrest until repaired
  • controlled by p53 protein

Question 3

S stage - synthesis of DNA

Answer 3

• cell replicates genetic material
• 2 chromatids (identical) per chromosome bound by centromere
• twice as much DNA as in G₁

Question 4

G₂ - postsynthesis gap

Answer 4

• another checkpoint
  
  • ensure enough organelles and cytoplasm for 2 cells
  • p53 helps
• check to avoid passing on DNA error that could replicate in future cells

Question 5

M stage - mitosis

Answer 5

• mitosis and cytokinesis
• prophase, metaphase, anaphase, telophase

Question 6

cyclins and CDKs

Answer 6

CDK - cyclin dependent kinase

• right cyclin must be present for CDK to be activated
• cyclin levels depend on stage of cell cycle
• activated CDK-cyclin complex phosphorylates transcription factors that promote transcription of genes for next stage of cell cycle

Question 7

Cancer fue to lack of cell cycle control

Answer 7

• mutate TP53, which is p53 gene
• cell does not stop damaged DNA
• accumulate mutations
• rapid division creates tumors
  
  • metastasis - spread of cancerous cells through bloodstream or lymphatics

Question 8

prophase - mitosis

Answer 8

• condense chromatin into chromosomes
• centriole pairs move to opposite poles
  
  • in the centrosome region that is outside of the nucleus
• nuclear envelope dissolves
• form spindle fibers made of microtubules
  
  • microtubule organizing center
• fibers radiate out of centrioles
• asters - microtubules that anchor centriole to membrane
• spindle apparatus uses kinetochore fibers to attach to chromosome at the kinetochores (proteins on centromeres)

Question 9

Metaphase - mitosis

Answer 9

• use kinetochore fibers and spindle apparatus to align chromosomes at metaphase/equatorial plate

Question 10

Anaphase - mitosis

Answer 10

• centromeres split
• sister chromatids split
• shorten kinetochore fibers to pull to poles

Question 11

Telophase/Cytokinesis - mitosis

Answer 11

• spindle apparatus disappears
• nuclear membrane forms
• nucleoli reappear
• chromosomes uncoil
• cytokinesis - speration of cytoplasm and organelles

Cell will divide 20-50 more times before programmed cell death

Question 12

meiosis overview

Answer 12

• in gametocytes or germ cells
• produces gametes - sex cells
  
  • not identical daughter cells
• one round of replication then 2 divisions
• meiosis I - seperate homologous chromosomes
  
  • reductional division
  • haploid daughter cells
• meiosis II - seperate sister chromatids
  
  • equational division

Question 13

prophase I - meiosis

Answer 13

• chromatin condense into chromosomes
• nuclear envelope disappears
• spindle apparatus forms
• synapsis - homologues intertwine
  
  • tetrad of 4 sister chromatids
  • held together by synaptonemal complex
• crossing over - chromatids break at chiasma and exchange equivalent pieces of DNA
  
  • occurs between homologues NOT sister chromatids
  • explains Mendel’s second law of independent assortment - inheritance of one allele has no effect on the likelihood of inheriting certain alleles
• recombination - result of crossing over
  
  • linkage is the tendency of genes to be inherited together
    
    • genes further from each other are less likely to be inherited together, but more likely to undergo recombination
    • produce more genetic diversity

Question 14

metaphase I - meiosis

Answer 14

• tetrads align at plate
• kinetochores attach to spindle fibers
  
  • one spindle fiber per chromosome (different than in mitosis)

Question 15

Anaphase I - meiosis

Answer 15

• disjunction - homologues seperate
  
  • Mendel’s first law of segregation
• segregation - seperation of 2 homologous chromosomes

Question 16

Telophase I - meiosis

Answer 16

• nuclear membrane forms
• each chromosome has 2 chromatids
• haploid cells
• cytokinesis - divide into 2 daughter cells
• interkinesis - between cell divisions of meiosis
  
  • chromosomes partially uncoil

Question 17

Meiosis II

Answer 17

• prophase - nuclear envelope dissolves
  
  • centrioles migrate to poles
  • spindle apparatus forms
• metaphase - chromosomes line up on plate
• anaphase - centromeres divide, chromosomes seperate into chromatids
• telophase - nuclear membrane forms
  
  • cytokinesis
  • up to 4 haploid daughter cells

Question 18

X chromosome

Answer 18

• carrys more info than Y chromosome
• causes sex linked disorders
  
  • males are hemizygous and express the disorder more frequently
• carriers - carry a diseased allele but do not express it
• most sex linked disorders are recessive

Question 19

y chromosome

Answer 19

• little genetic info
• SRY - sex determining region Y
  
  • codes for transcription factor that initiates testis differentiation and formation of male gonads
• Y chromosome present - male zygote
• absent - female zygote

Question 20

Male reproductive system

Answer 20

• seminiferous tubules - sperm produced here
  
  • nourished by Sertoli cells
• Interstitial cells (cells of Leydig) secrete testosterone and androgens
• epididymis - flagella gain mobility, stored for ejaculation
• vas deferens - tube from epididymis to ejaculatory duct
  
  • 2 ducts fuse to make urethra

Question 21

Semen

Answer 21

• sperm and seminal fluid
• mix with seminal fluid in reproductive tract
  
  • seminal vesicles - fructose for nourishment, alkaline properties
  • prostate gland - alkaline properties
  • bulbourethral (Cowpers) gland - clear fluid to clean urethra and lubricate

Question 22

stages of spermatogenesis

Answer 22

• spermatogenesis - formation of haploid sperm via meiosis, in seminiferous tubules of testes
• spermatogonia - diploid stem cell
• primary spermatocytes - after replication in S stage, now diploid
• secondary spermatocytes - after first meiotic division, haploid
• spermatids - after meiotic division II, haploid
• spermatozoa - mature spermatids
  
  • 4 sperm per spermatogonia

Question 23

sperm structure

Answer 23

• head - contains genes
• midpiece - make ATP
• flagellum - motility
• acrosome - head cap
  
  • made from golgi apparatus
  • penetrates ovum

Question 24

oogenesis

Answer 24

• production of female gametes
• primary oocytes - at birth, already undergone DNA replication, 2n, arrest in prophase I
• menarche - first mentral cycle
  
  • one primary oocyte per month completes meiosis I - makes a polar body and a secondary oocyte
  • unequal division
  • secondary oocyte arrested in metaphase II, only completed when fertilized

Question 25

Oocyte structure

Answer 25

• zona pellucida - surrounds oocyte, glycoprotein to protect adn compounds for sperm binding
• corona radiata - outside zona pellucida - layer of cells that adhere to oocyte during ovulation
• sperm cell penetrating triggers meiosis II to complete
• ovum provides all cytoplasm and organelles to zygote
• sperm and ovum join to make diploid zygote

Question 26

start of puberty hormones

Answer 26

• prior to puberty gonadotropin releasing hormone (GnRH) restricted by hypothalamus
• start of puberty pulses of GnRH trigger anterior pituiatry gland to synthesize and release follicle stimulating hormone (FSH) and luteinizing hormone (LH)
• FSH and LH trigger production of sex hormones

Question 27

male sexual development

Answer 27

• Y chromosome causes androgen production
• androgen production is low pre puberty
• FSH stimulate Sertoli cells - sperm maturation
• LH - interstitial cells to produce testosterone
• secondary sexual characteristics are caused by testosterone
  
  • facial and armpit hair, deep voice, increase growth
• testosterone - negative feedback on hypothalamus and anterior pituitary gland

Question 28

Estrogen

Answer 28

• produced by ovaries
• respond to FSH
• cause 2nd sex characteristics
• stimulate development of reproductive tract in embryo
• causes thickening of endometrium

Question 29

progesterone

Answer 29

• secreted by corpus luteum (remnant follicle after ovulation) in the ovary
• respond to LH
• development and maintanence of endometrium but not thicking
• after 1st trimester, placenta supplies progesterone
• corpus luteum atrophies

Question 30

Menstral cycle phases

Answer 30

• follicular, ovulation, luteal, menstration
• FSH begins maturation of ovum
• peak LH at day 14 for ovulation

Question 31

follicular phase

Answer 31

• begins with menses, shed lining
• High GnRH in response to low E and P, increase FSH and LH to respond
• develop ovarian follicles that produce E
  
  • neg feedback and lower GnRH, LH, and FSH
• E regrows lining
  
  • vascularization anf glandularization of decidua

Question 32

ovulation

Answer 32

• as estrogen increases it reaches a level that spikes GnRH, LH, and FSH
• LH spike causes ovulation of ovum into peritoneal cavity

Question 33

Luteal phase

Answer 33

• ruptured follicle forms corpus luteum - secretes P
• P rises and E already high
• High P is neg feedback that prevents GnRH, FSH, and LH from releasing more eggs

Question 34

Menstruation

Answer 34

• implantation does not occur
• LH stimulation of corpus luteum declines and P declines
• uterine lining sloughed off
• low P and E remove block on GnRH and next cycle can begin

Question 35

Post fertilization

Answer 35

• zygote to blastocyst anf implant in uterine lining
• secrete human chorionic gonadotropin (hCG)
• similar to LH and maintains corpus luteum
• E and P from corpus luteum keep uterine lining in place
• after 1st trimester, E and P produced by placenta and GnRH secretion is prevented

Question 36

Menopause

Answer 36

• less sensitive to FSH and LH
• ovarian atrophy
• endometrium atrophies and menstration stops
• E and P levels rise
• physical changes