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UB / Biology / BIO 130 / What are the principles of the cell theory of Schleiden and Schwann?

What are the principles of the cell theory of Schleiden and Schwann?

What are the principles of the cell theory of Schleiden and Schwann?



What are the principles of the cell theory of Schleiden and Schwann?

Key terms:​ yellow highlight Important to note: ​blue highlight 

1. What are the principles of the cell theory of Schleiden and Schwann, as formulated in 1938? Can you state all three?

a. The cell is the basic unit of life

b. All living things are composed of cells.

c. All cells originate from previously existing cells.

2. What are the three stages of ​interphase​? During which of these three stages do cells engage in DNA synthesis?… in synthesis of proteins for cell growth?...in synthesis of mRNA?

a. During M stage is the “mitotic phase” for mitosis (process) and cytokinesis, where actual cell division occurs. 

b. 1ST STEP:​ G1 phase is the gap between M and S stages where cells decide if they’re going to replicate or not - part of the CONTROL of the cell cycle. Don't forget about the age old question of What is General Motors Installment Plan?

c. 2ND STEP:​ S stage is “synthesis” for DNA replication. This is the semi conservative part of DNA replication.

What are the three stages of interphase?

d. 3RD STEP:​ G2 is the gap between S and M where preparations for M stage is made. This stage synthesizes the cell components for the daughter cells to have what they need to exist.

e. Protein synthesis is done during the stages of S, G1 and G2 (doubling the cell’s enzyme content.)

f. mRNA is made through transcription.

3. What is G​o ​and under what kinds of conditions is it evident? Does ​cell differentiation​ coincide with G​o​? Are ​DNA synthesis, RNA synthesis, protein synthesis​ evident during G​o​? We also discuss several other topics like What is anorexia?
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a. G0 means where cells go into a “quiescent” or rest stage where they don’t divide - during the G1 phase where it decides not to divide. b. Cell differentiation doesn’t coincide with G0, this stage occurs after M stage (when cytokinesis is done) but before S stage (DNA We also discuss several other topics like What are the four additional emotion coaching strategies for adolescents?


4. If mitosis starts with ​diploid, replicated​ chromosomes, what is the ploidy (​diploid, haploid, etc​) and replication status (​replicated or not

How does bilateral symmetry of the mitotic spindle figure into successful mitosis?

replicated​) of chromosomes in daughter nuclei after mitosis? Explain how replication and segregation ensure the outcome of mitosis. a. The ploidy of daughter nuclei after replication is 46 chromosomes with not replicated status.

b. Mitosis involves transferring the right chromosomes to daughter cells during somatic cell division, therefore after replication of forming two nuclei, cytokinesis occurs, separating the two new cells to ensure mitosis. 

5. In normal human mitosis, how many chromosomes are there at the spindle equator at metaphase? …how many chromatids are there at the spindle equator at metaphase? How many chromosomes are at each spindle pole at the completion of mitosis? Don't forget about the age old question of Correlation and relative age estimation of strata based on physical characteristics of rock layer, is what?

a. There are 46 chromosomes expected to be found at the spindle equator. 

b. There are 92 chromatids at the spindle equator.

c. Replicated chromosomes align at the spindle equator (metaphase) d. There are 46 chromosomes in each at the completion of mitosis. 6. How does bilateral symmetry (mirror-image nature) of sister chromatids figure into successful mitosis, i.e. proper spindle attachments and proper anaphase segregation? (Fig 8.17) When in the cell cycle (G​1​, G​2​, M, S) are spindle fiber attachments evident?...at which stage (G​1​, G​2​, M, S) is anaphase segregation evident?

a. A kinetochore is a structure assembled at the centromere during mitosis (circular shaped) where proteins bind to. This kinetochore connects the chromosome to the spindle fiber, which is important for spindle movement.

b. Then, anaphase segregation occurs, where spindle fibers shorten and exert a poleward pulling force to separate chromatids to opposite spindle poles. This results in each sister chromatid pulling into each new cell.

c. During S stage spindle fibers are evident.

d. During G2 anaphase segregation is evident.

7. How does bilateral symmetry of the mitotic spindle figure into successful mitosis?

a. Bilateral symmetry allows homologous chromosomes and their sister chromatids to successfully separate.

8. What is the chronological sequence of the​ anaphase, metaphase, prophase, prometaphase and telophase​? What are the defining features of each stage in regard to chromosomes?… in regard to the mitotic spindle?..in regard to kinetochore attachments to spindle fibers? We also discuss several other topics like what is the study of human evolution, fossil remains of humans, our ancestors, and other ancient primates?

a. The chronological process is prophase, prometaphase, metaphase, anaphase and telophase.

b. During prophase: DNA and its proteins start to condense. Nuclear membrane starts to disintegrate.

c. Prometaphase: chromosomes continue to condense and get attached to new spindle fibers become as they assemble,

kinetochores attach to opposite poles, chromatids start to separate to opposite ends of the cell.

d. Metaphase: cohesion, which holds two chromatids together is resisting how the spindle fibers are pulling the sister chromatids towards opposite poles.

e. Anaphase: these is a loss of cohesion resulting in the sister chromatids to move to opposite poles.

f. Telophase: this is where cytokinesis occurs.

9. What is the mechanism underlying ​separation​ of sister chromatids at anaphase onset? (hint: loss of coh - - - - -) What is the mechanism of segregation​ ​of sisters​ (i.e. ​movement of sisters to opposite poles​) during anaphase? Are poleward pulling forces involved?

a. Loss of cohesion. 

b. The segregation of sister chromatids occur when there is a loss of cohesion and the poleward pulling forces separate the sisters to opposite ends. - anaphase stage.

10.At which stage of mitosis are ​cohesin proteins​ cleaved and destroyed? What is the mechanism underlying this loss of ​cohesin proteins​?.. does it entail ​proteolysis​?

a. During anaphase stage the cohesion proteins are destroyed. This is proteolysis because enzymes are breaking down the cohesion proteins.

11. How do you define the term – ​cytokinesis?​ When (in G​1​, G​2​, M, or S) does cytokinesis occur?

a. Cytokinesis is the cytoplasmic division of a cell at the end of mitosis. This occurs at the end of M stage.

12. What are the defining characteristics of homologous chromosomes? In humans, how many pairs of homologous chromosomes are there?... are X and Y homologous?

a. Homologous chromosomes are chromosome pairs (one from each parent) that are similar in length, gene position, and centromere location. 

b. Humans have 22 pairs of homologous chromosomes. 

c. X and Y and partially homologous. 

13. Is pairing of homologous chromosomes necessary for mitosis (diploid to diploid)?...for meiosis (diploid to haploid)? What is the definition of a bivalent​? What roles do ​pairing​ and​ recombination​ of ​replicated homologous chromosomes have in creating ​bivalents.​ What is a cross-over​ (aka: ​chiasma​)? Do cross-overs take place between homologues or non-homologues?

a. Homologous pairs are necessary for mitosis, they need to pair up, also necessary during meiosis for haploidization, swapping segments from each parent chromosome.

b. Bivalent means, “homologous chromosomes associated in pairs” where the homologous pair exchange arm segments.

c. Chiasma, “cross-over” is the time where the exchange of arm segments take place (between paternal and maternal

chromosomes) in the 1st division of meiosis.

d. Cross-overs take place between homologues.

14. What triggers pre-meiotic cells to enter a meiotic pathway -- versus a mitotic pathway?

a. Retinoic acid triggers pre-meiotic cells to enter the meiotic pathway by acting on the germ cells at G1 phase.

15. Are chromosomes entering meiosis replicated or not replicated?… does DNA replication take place between the 1​st​ division and 2​nd​ division of meiosis? …are sister chromatids segregated together or away from each other during 1​st​ division?..during 2​nd​ division?..which one – 1​st​ division or 2​nd​ division – is a ​reduction division?​…which is an​ equational division​?

a. Chromosomes entering meiosis are replicated.

b. DNA replication does not take place between the 1st and 2nd division of meiosis. It takes place before, during interphase in the “S” stage.

c. During the 1st division, sister chromatids are segregated together, this is called the reduction division where homologues in a bivalent chromosome are separated from each other. Diploid to haploid. 

d. During the 2nd division, sister chromatids are segregated away from each other to opposite poles, this is called the equational division where the cohesion of sister chromatids break. Each former sister is a chromosome of its own. Haploid to haploid. 

16. Explain how chromosome replication followed by the two-step segregation plan of meiosis ensures making haploid gametic karyotypes from diploid progenitors.

a. After the mitosis process (see question #2) the human cell contains 23 bivalent chromosomes.

b. Then begins meiosis, during division #1 at prophase, the chromosomes pair with their homologue and the two swap segments at their chiasma.

c. Division #1 at metaphase, the kinetochores of each homologue connect to the same spindle pole, they are positioned to separate from each other.

d. Division #1 at anaphase, each replicated homologue is separated, one moving to the upper pole and the other the lower pole. This stage is when the reduction division is achieved, resulting in two haploids.

e. Division #2 at metaphase, the haploid chromosomes are positioned halfway between the two spindle poles and each sister chromatid is connected to opposite spindle poles.

f. Division #2 at anaphase, the cohesion between the sister chromatids split, making them segregate to the opposite poles. This results in an equational division where the daughter cells are now haploid.

17. How do Mendel’s First Law​ of segregation​ (Ch 3.4 Cummings) and Second Law​ of independent assortment​ (Ch 3.5 Cummings) relate to generating haploid from diploid?

a. Mendel’s first law is how homologues are detached from each other during the 1st division of meiosis.

b. Mendel’s second law is where the detachment of one pair of replicated homologues take place independently from other pairs of homologues.

c. These two laws explain the anaphase of division #1 where diploid chromosomes turn into haploid. 

18. Explain how ​independent assortment​ generates so many (i.e. 2 to the nth power -- ​2​n ​) combinations of maternally-derived and

paternally-derived chromosomes via chromosome segregation in meiosis. In the above, what does superscript ‘​n​’ stand for? (hint: hap - - - -)

a. Independent assortment means how there is no predetermined method in how bivalent chromosomes attach to the spindle pole and orient in what way, this occurs at random.

b. The subscript ‘n’ stands for the number of haploids.

c. Example: when there are two haploids, 2^2 =4, or 4 different possible combinations.

19. In the human testis, what are spermatogonial cells? … spermatocytes? … spermatids? … spermatozoa? In ovaries, what are oogonia, oocytes, follicle cells? Which of these cell types engage in meiosis? … what is the ploidy​ (i.e., ​haploid or diploid​), ​replication status (​i.e.,​ replicated or not replicated) ​, and ​actual number​ (i.e., ​23, 46, etc​) of chromosomes in each of these different human gonial cells: e.g. ​spermatogonia, spermatocytes, spermatids​, etc.?

a. Spermatogenesis is the production of haploid sperm cells from the male germ line that occurs after puberty.

i. The meiosis process starts off with a spermatocyte diploid replicated cell (23, X or 23, Y).

ii. The spermatocyte divides to be a haploid replicated cell after the first division of meiosis (23, X or 23, Y).

iii. At the second division of meiosis the spermatocyte divides again to make spermatids that are haploid and unreplicated (23 chromosomes).

iv. After this the spermatozoa form, which are mature sperm cells that lose substantial cytoplasmic mass in development and grows a long flagellum (23 chromosomes).

b. Oogenesis is the development of an ovum.

i. The process starts off with an immature oogonia cell that turns into a primary oocyte (which is haploid, replicated, 23 chromosomes) at the start of meiosis.

ii. Once the first division of meiosis is over, the secondary oocyte forms (along with polar bodies that are later

degraded) which is haploid, not replicated, 23 chromosomes. iii. Follicles are cells that surround the oocyte.

iv. Once the egg is fertilized when the sperm nucleus enters the egg cytoplasm, it becomes haploid with 46 chromosomes and not replicated.

20. Meiosis in a spermatocyte results in how many spermatids? How many fertilizable eggs come from meiosis of an oocyte? What are polar bodies? When are they generated?

a. Secondary spermatocytes that are haploid and replicated form 4 haploid unreplicated spermatids.

b. Meiosis of an oocyte forms 4 daughter cells, or 4 fertilized eggs. c. Once the first division is over, creating the secondary oocyte, that is when the first polar body is generated (total of three from after 2nd division).

d. A polar body is a haploid cell that is naturally formed like an egg but cannot be fertilized (non-functional) and later is degraded. 21. In human males, what is the pathway taken by sperm from the testes to ejaculation?... in which organ is meiosis completed?...in which organ is sperm maturation completed?

a. Sperm is generated in the testes by seminiferous tubules, which travel to the epididymis, flow through the vas deferens, joins the seminal vesicles/ejaculatory ducts, pass into the prostate gland, empty into the urethra, run through the bladder and penis for ejaculation.

b. Meiosis is completed in the testis and sperm maturation is completed in the epididymis.

22.In females, what is the pathway of an ovulated oocyte to the uterus?...in which organ is meiosis initiated?...completed? What triggers the progression from metaphase II (2​nd​ division metaphase) arrest through the completion of 2​nd​ division?...where does fertilization (i.e. union of haploid sperm with female gamete to establish diploid zygote) take place? What is the pathway of sperm to make contact with an unfertilized egg?

a. The secondary oocyte is released from the ovary during ovulation by cicilia into the oviduct (fallopian tube) and travels to the uterus. b. Meiosis starts during embryonic development in the ovaries and ends at ovulation when the egg is fertilized in the oviduct.

c. Fertilization completes the second division of meiosis.

d. The sperms makes contact with the unfertilized egg in the oviduct. 23.Regarding sperm, how do they differ morphologically from their progenitor spermatids? … in terms of “body” form? … in terms of nuclear content? … in terms of motile capabilities? What is an acrosome? … what does it do? Why is it important for fertilization? a. The progenitor spermatid is a spherical cell that is a haploid while a sperm loses most of its cytoplasmic mass, to swim quicker in its development and grows a long flagellum.

24.What is the difference between genotype and phenotype? What is a ​gene locus​? Is the locus of a given gene on one homologue at the same position as the gene’s locus on the other homologue?

a. A genotype is the alleles a person has (alternate forms of genes we get, one from mother and other from father.)

b. A phenotype is the actual expression of one’s alleles. (the gene that you actually express.)

c. A gene locus is the fixed position of a gene on a chromosome. d. A gene on one homologue is the same position as the gene in another homologue.

25.What is the definition of an allele of a gene?...what is a heterozygote? …what is a homozygote? What is the generally accepted explanation for why there are multiple alleles of a gene? In cases of complete dominance, which allele of a heterozygote is expressed?

a. An allele is one of the possible alternate forms of a gene.

b. A heterozygote is an individual with two alleles for a given gene that are different.

c. A homozygote is an individual with two alleles for a given gene that are the same.

d. There are multiple alleles of a gene because there are wild-type alleles and mutant alleles. 

e. In a heterozygote of complete dominance, the dominant allele is expressed.

26.Explain the alleles found in parent’s gametes in comparison to the alleles in the parent’s soma. How is it that a parent can transmit a recessive, non-expressed allele to an offspring generation? Is this explicable in terms of Mendelian genetics?...i.e. Mendel’s first law of segregation​?

a. The alleles found in a parent’s gametes are the same as the alleles in the parent’s soma.

b. As long as the parent has a recessive allele (even if they don’t express it) the allele can still be transmitted to their offspring. c. Mendel’s first law of segregation explains how homologues can detach from each other during the first stage of meiosis, after this occurs the swapping of genes between both parent chromosomes, which show how the offspring can receive a different set of alleles than their parents.

27.A man and a woman with normal skin pigmentation have a child who is albino. What is the suspected genotype of the parents? What is the probability that their next child will be albino? What is the probability that they could have a child with normal skin pigmentation?

a. The genotype of the parents is Aa (wild type allele A, which is dominant and mutant allele a).

b. There is a 25% chance their next child will be albino.

c. There is a 75% chance they will have normal skin pigmentation. d. Use the punnett square to find probability. 

28.Give a biochemical (enzymatic) explanation for the recessive phenotype called albinism.

a. The gene tyrosinase is an enzyme that leads to melanin biosynthesis.

b. The recessive phenotype for albinism is a mutant defective gene that codes for non-functional tyrosinase.

29.What is the explanation for multiple alleles of a gene (e.g​., I​A​, I​B​, and i alleles of the ABO blood type gene)? Why are these alleles said to be co-dominant? How does the function of the enzyme (glycosyl transferase) produced by the ​I​A​ allele differ from the transferase produced by the ​I​B ​allele? What is the phenotype of the ​i​ allele?

a. There are multiple alleles for the ABO blood type gene due to there being multiple types of glycosyl-transferase.

b. The alleles A and B are codominant, where there is a full phenotype expression of both alleles of a gene pair.

c. The A allele has the enzyme, glycosyl-transferase that adds N-acetylgalactosamine to red blood cells while in the B allele, glycosyl-transferase adds galactose to the red blood cell


d. The phenotype of the i allele (two of the recessive i alleles form O blood type) has neither terminal sugar (no N-acetylgalactosamine nor galactose).

30.If you have type A blood, which of the alleles --​ I​A​, I​B​, or i​ – might you have? If you have type O blood, which of the alleles (and how many) of them do you have? Where in your body are the gene products (proteins) of these different alleles evident?

a. If you have A blood type you can have the A allele or i allele. b. If you have O blood type, you have two of the recessive i allele. c. The proteins of these different alleles are present in your red blood cells.

31. Consider incomplete dominance. How do the dominant and recessive alleles of a heterozygote figure into the observed phenotype? Explain incomplete dominance in the case of flower color covered by Cummings on p. 60 (Figure 3.18).

a. In incomplete dominance, both alleles are expressed.

b. In a heterozygote with both dominant and recessive alleles, the dominant allele is expressed in the phenotype.

c. For the snapdragon flowers, both the red and white colors are dominant, therefore when these flowers are crossed, they produce pink flowers.

32.What is LDL? Explain incomplete dominance in the case of LDL receptor proteins on target cells that take up LDL. How do the dominant and recessive alleles affect phenotype? How do LDL receptors figure into the phenotype called familial hypercholesterolemia?

a. LDL is a “lousy” cholesterol protein that carries cholesterol and lipids to cells that use if for maintenance and synthesis.

b. The dominant allele is H which produces a transmembrane receptor for LDL.

c. The recessive alle is h which degrades before it can be inserted into the surface membrane of cells.

d. Therefore, only individuals with two recessive h allele have the defective LDL receptor.

e. Familial hypercholesterolemia (FH) can be caused by heterozygotes (Hh) that cause a less severe case of high blood cholesterol and heart disease by 50. For homozygotes (hh) causes a extremely severe case of FH of very high blood cholesterol and early

childhood death.

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