mcat science 8

  1. tertiary  protein structure- interaction between side chains of amino acids

    disulfide bonds -
    - ionic interactions between side chains
    - cross-link within chains
  2. conjugated protein- contains prosthetic group that doesn't consist of amino acids

    ex- heme group found in hemoglobin
  3. enzyme concentration increase = vmax increase
  4. higher Km = lower affinity for substrate = slow step = rate limiting step in comparison to other steps
  5. enzymes lower activation energy of reverse and forward reactions
  6. Kinesins or dynein

    _____ used in metaphase and anaphase of mitosis 

    _____ used in cilia/flagella movement and vesicle transport but not mitosis
    kinesins

    dyneins
  7. NMR Spec & isoelectric focusing - identify molecules

    Affinity chromatography & size exclusion - separate

    affinity chromatography would be best for isolating myglobin from ground beef due to nickle binding to histidine on myglobin
  8. DNA gyrase (class II topoisomerase) is responsible for uncoiling the DNA ahead of the replication fork. Tight coiling of DNA would halt replication because movement of the replication complex would be energetically impossible
  9. DNA replication stops for ddNTP and not dNTP because the phosphate of the next nucleotide is unable to attach without 3` O.
  10. 5` guanine cap added during transcription and poly-A tail added ______ transcription
    after

    poly A isn't added until elongation is complete
  11. which add hydrophillic group and which adds hydrophobic group?

    prenylation
    hydroxylation
    glycosylation
    phosphorylation
    • prenylation - hydrophobic
    • hydroxylation - hydrophillic
    • glycosylation - hydrophillic
    • phosphorylation - hydrophillic
  12. in absence of repressor protein/ regulator gene for lac operon the lac genes would be expressed constituitevely
  13. no/ low glucose and high lactose lead to high levels of mRNA for lac operon
  14. no lactose means repressor stays bound to operator and no transcription takes place

    lactose present means it binds to repressor and repressor dissociates from lac operon and transcription can take place
    -----------------------

    when tryptophan present it binds to repressor which binds to operator and no transcription takes place

    when tryptophan absent repressor dissociates from operon and transcription takes place
  15. lipids are anchored to phospholipids and phospholipid head requires energy to transverse the hydrophobic membrane through enzymatic assistance of ________
    flippases
  16. loss of enzyme / active sites does what to vmax?
    lower vmax
  17. Pyruvate dehydrogenase converts pyruvate to _______ and what is a co-factor for this reaCTION?
    acetyl CoA

    thiamine and magnesium
  18. Glycogen in muscle and liver

    Liver- needs to release glucose systemically so its activated by glucagon. Liver cells are activated by insulin to release glucose after each meal.

    muscle utilizes its own glycogen and is stimulated by AMP to release glucose for intracellular metabolism. lacks glucose-6-phosphotase to deliver glucose systemically the way liver does and keeps glucose for itself
  19. Acetyl-CoA is produced by metabolism of 

    fatty acids - ex- linoleic acid
    amino acids - ex - alanine 
    carbs - sucrose
  20. epinephrine requires ______ hormone to have an effect on metabolism
    thyroid hormone
  21. because adipose lack glycerol kinase  it reduces dihydroxyacetone phosphate to produce glycerol 3 phosphate
  22. deltaG positive = nonspontaneous = Ecell negative

    delta G negative = spontaneous = Ecell +
  23. flavoproteins

    - cofactor for pyruvate decarboxylation
    - B vitamin modification and activation
    - electron carrier in chloroplasts
  24. cardiac muscle uses fatty acids in starvation and well fed states - unique
  25. passive transport -
    diffusion and osmosis
    ---------------------------


    active transport-

    pinocytosis- cell drinking engulf extracellular fluids with any solutes in it, also a form of endocytosis

    phagocytosis - eating cells, larger molecules like bacteria

    receptor mediated endocytosis
  26. prokaryotes - ______ chromosomes

    eukaryotes - ______ chromosomes
    circular

    linear
  27. splicing occurs in the _____ in eukaryotes
    nucleus
  28. Development of the mesoderm leads to the growth of a coelom, inside of which growing organs are protected. The mesoderm can develop into multiple sub-mesodermal tissues. Which of the following pairings correctly matches a sub-mesodermal tissue layer with its corresponding tissue? 


    A. Intermediate mesoderm – respiratory lining 


    B. Paraxial mesoderm – spinal cord 


    C. Lateral plate mesoderm – urinary bladder 


    D. Chorda-mesoderm – notochord
    D is correct. The chorda-mesoderm, as its name implies, develops into the notochord. The intermediate mesoderm develops into gonads and kidneys, the lateral plate mesoderm develops into the gut wall and circulatory system, and the paraxial mesoderm develops into skeletal muscle and cartilage. However, you can answer this question without knowing these facts, as the other three tissues are not mesodermal at all.




    A, C: The lining of the respiratory tract and the bladder are derived from the endoderm.




    B: The spinal cord, as well as the rest of the central nervous system, arises from ectodermal tissue.
  29. During _______, microtubules must locate and attach to kinetochores and pull chromosomes to the center of the cell. This requires proper functioning of tubulin-based microtubules.




     DNA replication occurs during the ____ phase of the cell cycle.




     DNA condensation occurs during ______.




     The nuclear envelope re-forms during ______
    metaphase

    S

    prophase

    telophase
  30. differences between meiosis 1 and 2:

    I. Meiosis I is a heterotypic division, while meiosis II is a homotypic division.  

    II. Crossing over occurs only during meiosis I.  

    IV. A long S phase precedes meiosis I, but no S phase comes before meiosis II.

    -----



    Meiosis I is a heterotypic, or reductional, division. In other words, parent cells begin as diploid, while daughter cells formed during meiosis I are haploid. Remember this for the MCAT – a very common misperception is that cells are still diploid at the beginning of meiosis II! Instead, meiosis II is a homotypic, or equational, division, making choice I correct. Statement II is also sensible, as genetic diversity is enhanced by crossing over between homologous chromosomes during meiosis I, but no such event occurs during meiosis II. Lastly, the cell replicates its DNA during the S phase prior to meiosis I, but no additional replication precedes meiosis II. This results in the overall transition from diploid to haploid.




    III: DNA is always highly conserved. Although mutations are a source of diversity, they are usually dangerous for the organism. Consequently, meiosis II does not include intentional mutagenesis. Instead, genetic diversity arises from the random assortment of chromosomes and from crossing over.
  31. G1 is longest time period of interphase

    During the G1 phase, the cell conducts protein and organelle synthesis at a high rate while the cell grows in size. The transition from the G1 to the S phase is termed the “restriction point” and constitutes the rate-limiting step in the cell cycle.
  32. which checkpoint? g2-M or g1-S

    - ensures that the DNA has been replicated accurately

    - ensures that the cell is of sufficient size to undergo mitosis
    g2-M

    G1-S checkpoint
  33. Cyclin and cyclin-dependent kinases (Cdks) play an essential role in the regulation of the cell cycle. If a cell from a mutated line displays permanently reduced levels of both cyclin and Cdks, which consequence is most likely? 


    A. The cell cycle would be prevented from occurring. 

    Cyclin and Cdks are crucial cell cycle regulators. Depending on the phase of the cycle, certain Cdks will be expressed at higher concentrations than others; this signals the cell to prepare for the next transition. In other words, the levels of these proteins are dynamic throughout the cell cycle. If this cell has perpetually low concentrations of cyclin and Cdks, it lacks the signaling molecules required to initiate and prep the cell for upcoming phases.
  34. A. Apoptosis is a naturally-triggered event, while necrosis involves uncontrolled cell death. 


    B. Apoptosis produces no inflammation.


    C. Necrosis is typically caused by bacterial or fungal infections, while apoptosis is a process stimulated by signals within the cell. 


    D. Necrosis usually requires medical treatment, while apoptosis typically resolves itself without external attention.
  35. what germ layer?


    B. Lining of internal organs (stomach, lungs, intestines, etc.)  


    C. Muscle, cardiac and skeletal systems, blood, heart, spleen 


    D. Epidermis, nervous system, lens of the eye, hair
    ENDODERM

    B. Lining of internal organs (stomach, lungs, intestines, etc.)  


    mesoderm

    C. Muscle, cardiac and skeletal systems, blood, heart, spleen 


    ectoderm

    D. Epidermis, nervous system, lens of the eye, hair
  36. cells progress from totipotency to pluripotency to multipotency
    cells progress from totipotency to pluripotency to multipotency
  37. The table shows that progesterone concentrations are low throughout the cycle, with the exception of a peak around day 21. This increase is promoted by ovulation, in which a follicle bursts and releases a secondary oocyte. The remainder of the follicle gives rise to the corpus luteum, which directly releases progesterone and estradiol.

     the surge in LH that stimulates ovulation
  38. Typically, estrogen and progesterone negatively feed back on gonadotropin-releasing hormone (GnRH). As a result, high levels of these steroids lead to reduced release of LH and FSH. As a surge in LH is required to stimulate ovulation, persistently high progesterone levels near the beginning of the menstrual cycle will prevent this woman from ovulating – at least until the effects wear off.
  39. Meiosis typically produces four haploid cells. Why, then, does each primary oocyte give rise only to a single ovum?
    The remaining daughter cells, known as polar bodies, are small enough to allow the ovum to keep the majority of the original cytosol and organelles. 

    One round of oogenesis yields one ovum and multiple small, dark polar bodies. These “extra” cells later undergo apoptosis. As a result of this phenomenon, the ovum (which is very demanding of both nutrients and energy) is able to retain most of the original organelles and cytosol.
  40. true regarding spermatogenesis:

    II. In a secondary spermatocyte, sister chromatids are still paired in the same cell. 

     meiosis I produces secondary spermatocytes.
  41. Spermatagonium

    2n - primary spermatocyte

    meiosis 1 - separation of homologous chromosomes 

    n - secondary spermatocyte (two)

    meiosis 2- separation of sister chromatids 

    spermatids (4) --- > spermatozoa
  42. the blastopore becomes the ____ in deuterostomes and ____ and protostome
    anus

    mouth
  43. zygote -- > 2 -> 4 -> 8 -> -> 16 (morula) -> blastula - > gastrula - > neurula
  44. _____ develops into the central nervous system, which includes the brain and spinal cord.

    The _____ provides the primitive axis of the developing embryo and, in vertebrates, develops into the vertebral column.
    The neural tube

    notochord
  45. this  correctly describes the fluid mosaic model:

    Plasma membranes act as two-dimensional fluids that allow for the free diffusion of proteins and lipids within the leaflet.
  46. Cholesterol and similar molecules, which act as a type of buffer system for membrane fluidity, are slightly more complex. Large amounts of cholesterol decrease fluidity at high temperatures but increase it at low temperatures.
  47. these statements accurately identify a function of transmembrane proteins:

    I. They act as receptors for hormones and initiate signal transduction pathways.  
    II. They allow for transport of charged molecules across the cell membrane.  
    III. They are responsible for the production of the majority of the ATP synthesized in eukaryotic cells.

    Transmembrane proteins, such G protein-coupled receptors, bind hormones and other ligands to activate signal transduction pathways. This activation ultimately results in a change in gene expression. Additionally, statement II is accurate, as such proteins may form channels that allow charged molecules to pass. Finally, while not embedded in the overall lipid bilayer of the cell, ATP synthase spans the inner mitochondrial membrane and is therefore a transmembrane protein.
  48. If transport stops when manganese has reached equilibrium, the ion must not be moving against its concentration gradient, making this some form of passive transport. Since manganese is charged, it must use a protein channel to enter the cell. It can't just diffuse through the plasma membrane
  49. The slender giant moray (Strophidon sathete) is a species of large marine eel that is technically classified within the moray family. Like most oceanic creatures, the giant moray has adapted to have different intracellular solute concentrations than freshwater animals. If one of these marine eels were placed in a typical river, its cells would:

    swell, as they would be hypertonic to their environment. 

    From the question stem, we can assume that the cells of a moray eel are more highly concentrated in solute than those of a typical freshwater species. This is likely true because the ocean is extremely salty, and a cell must have a tonicity that is relatively similar to that of its environment to avoid losing or gaining water. In other words, moray cells are hypertonic to fresh water. When placed in a river, which is almost certainly much less salty than the ocean, these cells will swell as water flows down its concentration gradient from low to high solute.
  50. In normal human extracellular fluid, the concentration of Na+ is approximately 140 mEq/L. A beaker of water is filled with a solution with exactly that sodium concentration. If a water-permeable synthetic cell is dropped in the beaker, what NaCl concentration can it have and still lose water to its environment? 

    [NaCl] < 70 mEq/L 

    For a water-permeable (but not solute-permeable) cell to lose water via osmosis, its contents must be hypotonic relative to its environment. In other words, it must include relatively less solute. Here, the extracellular fluid has a sodium ion concentration of 140 mEq/L, meaning that any cell with a smaller ion concentration should leak water. However, NaCl is virtually completely soluble in water, so 70 mEq/L of NaCl will dissociate into 140 mEq/L Na + and Cl- ions.
  51. The Na +/Ca2+ exchanger, an antiport transport protein, utilizes the concentration gradient of sodium to actively force calcium ions across the cell membrane. Given this information, the Na+/Ca2+ exchanger must: 

    move calcium ions out of the cell. 

    Antiporters move two different ions or molecules in opposite directions across a membrane. Here, we know that sodium’s concentration gradient is used to power the movement of calcium. Since sodium tends to be far more highly concentrated outside the cell (due to the action of the sodium-potassium pump), it will flow inward when allowed to move down its gradient. Since Na+ and Ca2+ move in different directions, calcium ions must exit the cell.
  52. After a molecule has been engulfed via endocytosis, in what order does it progress through membrane-bound compartments before it is degraded? 


    A. Early endosome, late endosome, lysosome
  53. A. The mitochondrion likely originated as an independent prokaryotic organism that was engulfed by an early eukaryote. 


    B. Mitochondria have their own set of DNA that is entirely separate from the nuclear genome. 


    C. Mitochondria are able to replicate in a fashion that is independent of cell replication. 

    A-C = TRUE!

    The most popular theory for the origin of the mitochondrion is known as the endosymbiotic hypothesis. This theory states that these organelles began as small, independent prokaryotic organisms that entered into a symbiotic relationship with a eukaryotic cell. Additionally, mitochondria have a separate set of DNA that, unlike nuclear DNA, is inherited maternally. They are also able to replicate outside of cell replication.
  54. Lysosomes function to digest toxins, proteins, and unusable cellular macromolecules. These organelles are membrane-bound and contain enzymes that function at low pH. If a cell displays increased lysosome synthesis, it likely experienced a recent need for digestion of such molecules. This could easily be due to some form of toxin or injury to the cell.
  55. A. Packaging of proteins in vesicles for transport to other parts of the cell 


    B. Targeting of proteins for excretion 


    C. Production of lysosomes 

    these are all functions of _______

     Production of the enzymes found within peroxisomes  is function of ______
    Golgi apparatus

    ribosomes since they make proteins which most enzymes are made of
  56. The membrane of the endoplasmic reticulum is an extension of the outer leaflet of the nuclear envelope. Its removal would greatly diminish overall nuclear integrity, likely causing that organelle to lyse. As this would almost certainly trigger apoptosis
  57. ______ are small membrane-bound organelles that function mainly to break down lipids. In contrast, _______ facilitate the enzymatic catabolism of protein.
    Peroxisomes

    lysosomes
  58. I. Rough ER – synthesis of transmembrane proteins  
    II. Nucleolus – rRNA production and ribosome assembly
  59. A patient with persistent difficulties fighting off bacterial infections is found to have a genetic mutation that adversely affects the speed of phagocytosis in macrophages. This mutation most likely impairs which type of cytoskeletal polymer?

    Actin filaments 

    Macrophages must undergo rapid actin reorganization during phagocytosis. If a macrophage cannot engulf bacteria in this manner, its overall function would be considered very impaired.
  60. A middle-aged man has a condition that impairs the synthesis of microtubule linking proteins. This disorder most likely impairs the function of spermatozoa.

    Microtubule linking proteins, as their name implies, are used to bind bundles of microtubules together. This is most notably observed in eukaryotic flagella. If these proteins cannot be synthesized, flagella will not work properly, and the function of cells that rely on these structures will be diminished. Of the listed cells, only spermatozoa (sperm cells) possess flagella.
  61. Which of the following cytoskeletal proteins contributes the most to the skin’s resistance to stretching and tearing?
    keratin
  62. From the table, we see that type C has the largest diameter, which is characteristic of microtubules. Additionally, microtubules are known for their rigidity, and type C is listed as the most rigid of the polymers. As some of the longest cells in the body, neurons rely on microtubules to transport neurotransmitter-containing vesicles and macromolecules along their axons. Therefore, one can expect to find the longest type C polymers in neural cells like those in the cerebral cortex.
  63. Cytokinesis involves a contracting ring of actin microfilaments that pinches the two daughter cells apart. Preventing actin monomers from polymerizing will inhibit the filament reorganization necessary for cytokinesis to occur.
  64. gram (-) = thin cell wall / outer membrane present 

    gram (+) = thick cell wall / outer membrane absent
  65. eukaryote  or not?

    fungi
    archaea
    plant
    bacteriophage
    • fungi - eukaryote
    • archaea - not, single celled
    • plant - eukaryote
    • bacteriophage - not living
  66. rod shaped vs circular shaped

    bacilli 

    cocci
    bacilli - rod

    cocci - sphere
  67. Archaea, once known as archaebacteria, are classified as prokaryotes. As such, they do not possess membranous organelles.




    B: Protozoa are classified as part of the kingdom Protista. Although these organisms are unicellular and simple, they are eukaryotic. All eukaryotic cells possess membrane-bound organelles.




    C: Hyphae are long filament-like structures that comprise parts of fungal organisms. Remember, fungi are eukaryotes.




    D: Human cells, including neurons, are eukaryotic.
  68. Eukaryotes perform aerobic respiration in the mitochondria by pumping protons into the intermembrane space. What membrane do prokaryotes use to perform this function?
    The plasma membrane 

    Prokaryotes lack membrane-bound organelles and therefore cannot use either mitochondrial membrane. In addition, not all prokaryotes have cell walls. This leaves the plasma membrane as the most likely structure across which a proton gradient is established.
  69. Which organisms are dependent on the electron transport chain to create ATP?

    All obligate aerobes
  70. Organisms can obtain energy either from light (“photo-”) or organic or inorganic electron-containing compounds (“chemo-”). Since this bacterium grows only when it is exposed to light, it must be a phototroph. Additionally, autotrophs can fix carbon from CO2 in the atmosphere; thus, they do not need to be given pre-existing organic macromolecules. Since Heliobacteria dies unless it is grown on enriched media, it appears to be heterotrophic.
  71. One characteristic of prokaryotic, but not eukaryotic, transcription is that

    mRNA does not undergo post-transcriptional modification. Eukaryotic mRNA is produced in the nucleus, but must be exported to ribosomes in the cytoplasm for translation. To prepare a transcript for this process, it is modified by the addition of a 5’ cap and a 3’ poly(A) tail; additionally, its introns are spliced out by cellular machinery. Prokaryotic mRNA transcripts are not modified in this manner.
  72. _______ a bacterium exchanges genetic material with another cell via a specialized sex pilus. 


    ________ a bacteriophage transfers genetic material from one bacterial cell to another during infection. 


    ________ a prokaryotic cell acquires genetic material from its external environment.
    conjugation

    transduction 

    transformation
  73. Class I transposons (retrotransposon) are known as “copy-and-paste” transposons, as they involve the creation of a new copy of the transposable element. These elements first undergo transcription into RNA using RNA polymerase; as their name implies, they are then reverse transcribed back into DNA and placed in a distinct location elsewhere in the genome.

    Class II, or “cut-and-paste,” transposon. an end result of the same total number of transposons.
  74. Most viruses have only one or two genes coding for capsid proteins. 



     Most viral capsids are composed of repeated identical monomers, reducing the need for a large genome containing multiple different genes for structurally distinct capsid proteins.




    A: Viral capsids tend to be spherical or otherwise geometrically regular. Since the structure is formed from hundreds of identically-shaped protein monomers, physical constraints are placed on the ultimate shape of the virus.




    B: The capsid is made from noncovalently-associated protein subunits, not lipids.




    D: In general, the capsid assembles spontaneously around the genetic material. It sometimes requires viral enzymes for complete assembly, but never ribosomes. Ribosomes assemble polypeptides from individual aminoacyl-tRNA molecules and have no impact on intact proteins.
  75. Reverse transcriptase first synthesizes a single strand of DNA from the viral RNA template. It then synthesizes a second complementary strand of DNA using the first DNA strand as a template.

    so it uses RNA and DNA as a template

    it is carried within the retroviral capsid and released into the cytosol following viral penetration
  76. Prions tend to induce misfolding and aggregation of endogenous cellular proteins, forming highly stable amyloid fibers. The natural cellular response to the presence of misfolded proteins is the production of heat shock proteins, which help to properly fold the defective protein molecules. The absence of heat shock activity suggests that the cell is not experiencing any problems with protein aggregation, which is one of the hallmarks of prion disease pathology.
  77. The two most commonly encountered secondary structures of a polypeptide chain are α-helices and β-pleated sheets. Secondary structure refers to the shape of a folding protein due exclusively to hydrogen bonding between its backbone amide and carbonyl groups. Secondary structure does not include bonding between the R-groups of amino acids, hydrophobic interactions, or other interactions associated with tertiary structure.
  78. A ______ is a reduction in gene-pool diversity because of a sharp reduction in population size.
    genetic bottle
  79. hardy

    P^2 + 2PQ + Q^2 = 1

    P + Q = 1

    P^2 = Prevalence if homo dom (proportion)
    Q^2 = Prevalence of homo recessive (proportion)

    2pq = frequency of hetero
    P = frequency of dom allele
    q = frequency of recessive allelle

    2pq x total # = prevalence of hetero (proportion)
  80. ______ speciation occurs because of physical barriers. Geographic isolation is an example.

    _______ speciation describes reproductive isolation that emerges when no physical barrier separates a population.
    Allopatric

    Sympatric
  81. In the G2 phase, how many autosomal chromatids exist in a C. lectularius somatic cell? it has 26 autosomal chromosomes
    104

    Somatic cells (non-reproductive cells) are generally diploid. This means that they have two chromatids for each chromosome. Paragraph 2 explains that this species contains 26 autosomal chromosomes. For C. lectularius this means a total of 52 autosomal chromatids in a cell not undergoing cell division. However, during the S phase of the cell cycle, each chromosome (and therefore each chromatid) is duplicated. This results in 104 autosomal chromatids in the G2 phase (before mitotic division) for an organism with 26 autosomal chromosomes.
  82. Out of a group of individuals carrying a genotype, penetrance reflects the proportion who express it. Paragraph two explains that all individuals in the African stock are homozygous for recessive pyrethroid resistant alleles but here only 60 are expressing that resistance. Therefore, penetrance is incomplete. Expressiveness reflects the strength with which the phenotype is expressed. The participants experienced no negative consequences because of their exposure. This suggests the phenotype, when expressed, was expressed completely.
  83. aldosterone- Na+ reabsorbed into blood and K+ excreted so issue with kidney that leads to low sodium in blood means more K+ in blood



    Aldosterone’s function is to act on the principal cells of the distal tubule and the collecting duct of the nephron, to upregulate and activate the basolateral Na+/K+ pumps, which pump three sodium ions out of the cell into the interstitial fluid, and two potassium ions into the cell from the interstitial fluid. This creates a concentration gradient which results in reabsorption of Na+ and water into the blood, and the secretion of K+ into the lumen of collecting duct and eventually the urine.
  84. An enhancer is a short segment of DNA that can be bound by transcription factors (activators) to enhance transcription of a gene or genes. Enhancers are generally cis-acting, but can be upstream or downstream from the transcriptional start site.

    A promoter is a region of DNA that initiates transcription of a particular gene. Promoters are located near the transcription start sites of genes, on the same strand and upstream on the DNA (towards the 5' region of the sense strand)
  85. stomach --> duodenum --> jejunum -- > ileum ---> Large intestine (cecum --> colon --ascending -- transverse -- descending -- sigmoid ---> rectum)
  86. The thyroid hormone T3 and its prohormone T4 are modified amino-acid hormones that behave much like steroid hormones in their global regulation of metabolism, transport-protein binding in the blood, and in their binding of the thyroid hormone receptor—a nuclear receptor.

     vasopressin - peptide hormones



     FSH - peptide hormone

     serotonin - peptide hormone
  87. Diagnosis of major depressive disorder requires at least one of the two major symptoms of depressed mood (sadness) or lack of pleasure (anhedonia).
  88. Phototransduction is the process by which light is converted into electrical signals in the rods, cones, and photosensitive ganglion cells of the retina of the eye. This would be the logical next step after light hits the rods and cones as mentioned in paragraph one. 

    A: Repolarization is the process by which neuronal membranes return to their negative resting potential after an action potential is sent. 

    C: Phototaxis is the movement of an organism towards or away from a light source. 

    D: Thermosensation is the sensation of temperature by the body, not light.
  89. The exchange of genetic information between homologous chromosomes occurs in which stage of cell division? 

    Prophase I 

    Crossing over is unique to meiosis, a specialized type of cell division that occurs only in germ cells. It occurs in prophase I of meiosis.
  90. The restriction point, or the point at which a cell is committed to undergoing mitosis, is located in which stage of interphase?
    G1

    The restriction point is a point in G1 of the cell cycle, and after it is passed the cell is committed to division.
  91. Mitosis produces 2 diploid genetically identical daughter cells while meiosis produces 4 haploid daughter cells that are genetically distinct. Mitosis proceeds through one round of cell division while meiotic cells undergo two rounds.
  92. Anaphase 1 is that phase in which homologous chromosomes separate to each side of the cell, and the centromere is intact while in anaphase 2, the sister chromatids separate and the centromere splits into two which result in two separate chromatids.
Author
JAM41MAN
ID
341528
Card Set
mcat science 8
Description
erw
Updated