Cell theory 3

Question 1

Indirect active transport example and explanation

Answer 1

sodium-glucose cotransporters move Na+ and glucose together into the cell – Na+ moves down its C gradient, releasing ATP in the process, and glucose uses this ATP to move against its C gradient. This type of transport depends on the Na+ pump to pump ions back out and maintain the sodium gradient (kidneys during reabsorption of glucose and in the small intestine during the absorption of glucose from digested foods)

Question 2

How does the cell wall protect a cell in hyper and how in hypotonic environments?

Answer 2

can only protect the cell in a hypotonic environment by keeping it from bursting (it maintains its shape and keeps it turgid) but in hypertonic, the plasma membrane simply detaches from the cell wall and the cell shrinks as it dehydrates (together with its vacuole)

Question 3

Plasmolysis and deplasmolysis

Answer 3

when water leaves a cell in a hypertonic environment so it shrinks, the plasma membrane detaches from the cell wall, and the vacuole dehydrates – deplasmolysis is when water renters the cell that went through plasmolysis (the cell’s volume increases and the membrane attaches to the cell wall)

Question 4

What are three mechanisms for preventing the cell from bursting in a hypotonic solution?

Answer 4

1| Cell wall protection
2| Using contractile vacuoles (E from ATP used to pump ions into the CV so that the water from the cytoplasm enters – CV merges with the plasma membrane and water is removed by exocytosis)
3| Maintaining the concentration of the extracellular fluid (multicellular organisms – kidneys)

Question 5

Water potential

Answer 5

a potential F held by water per unit of volume maximal in pure water (0 kPa) because the effective number of water molecules is reduced when it is bound to solute molecules (can’t move freely then) – depends on solute potential and pressure potential (the higher the hydrostatic pressure, the higher the WP) – water moves from higher WP to lower WP

Question 6

Endocytosis and exocytosis

Answer 6

the active transport of large particles or entire cells across the membrane by means of vesicles possible due to the fluidity of the membrane – in endocytosis, vesicles are brought to lysosomes where the enzymes digest the engulfed substances

Question 7

Freshwater vs ocean fish (type of environment which affects whether water goes out or in, volume and concentration of the urine, which way active transport occurs and whether fish have to drink water)

Answer 7

freshwater: hypotonic environment, water into, large urine V, diluted urine, active transport into, and doesn’t drink water
vice versa for ocean fish

Question 8

What are morphogens and how do they perform their function?

Answer 8

chemical signals released by some cells during the blastocyst stage that start the cell specialization process in an embryo – get released and diffuse and cells specialize according to what concentration of morphogens they are exposed to (morphogen gradient indicates to a cell its position in the embryo) because they impact gene expression

Question 9

Stem cells and different types

Answer 9

cells with the ability to divide endlessly and differentiate along different pathways – totipotent, pluripotent and multipotent (tissue specific)

Question 10

Differentiate between different STEM cell types

Answer 10

totipotent can become any cell type in the body (body and placenta), have all genes switched on/expressed – pluripotent can become any type of cell in the body but not the placenta (in the blastocyst, the inner cell mass) – multipotent can develop into cells within a narrow group like liver, skin, and hematopoietic SC in bone marrow (regeneration of adult tissues)

Question 11

What is SC niche?

Answer 11

the precise location of SC in the organism – place where SC can either remain inactive for a long period or proliferate and rapidly differentiate (these are determined by the microenvironment of the niche) – exist only for multipotent SC (bone marrow and hair follicles)

Question 12

What does cell V determine and what does cell SA determine, what happens when V exceeds the SA capacity?

Answer 12

V determines the rate of metabolism (the amount of substances transported in and out of the cell)
SA determines the effectiveness of the exchange of materials
the cell dies (SA/V ratio too small) or, to prevent that, divides

Question 13

Ligand and describe ligand action

Answer 13

a molecule that binds selectively to a specific site on another molecule released by a source and affecting target cells – binds to the receptors on the target cell and causes changes in the receptor’s conformation which is recognized by other processes in the cell, the signal is passed on and the cell changes its behavior (metabolic activity)

Question 14

Signal transduction pathway and what are two types according to two different types of ligand receptors?

Answer 14

the sequence of interactions in cells triggered by ligand binding – transmembrane STP (on the cell’s surface) and intracellular STP (in the cell cytoplasm)

Question 15

Transmembrane STP steps

Answer 15

1| Reception – binding causes a reversible conformational change of the receptor
2| Signal transduction – the newly catalytically active receptor causes the production of a secondary messenger within the cell
3| Response - activation of cellular responses – signal is carried by the secondary messenger to effectors that carry out the response

Question 16

Intracellular STP steps

Answer 16

1| Steroid hormone enters the cell (hydrophobic)
2| Hormone-receptor complex formed
3| Complex travels to the nucleus where it binds to the promotor region on the DNA and directly controls the gene expression process

Question 17

The requirements for a signaling chemical

Answer 17

1) Has a distinctive shape and chemical properties so the receptor can distinguish between it and other chemicals
2) Is small and soluble enough to be transported

Question 18

Different types of ligands

Answer 18

hormones, neurotransmitters, cytokines and Ca ions

Question 19

Hormones (chemical nature, source, where it goes from the source, target cell(s), how it affects the TC, speed/longevity of the effect, examples)

Answer 19

can have complex and widespread effects on the body – can be amines, peptides, or steroids, released by groups of specialized cells in glands, travel through blood to all body cells, they inhibit/promote processes (changes in gene expression) and have long-lasting effects – e.g. insulin, thyroxin, testosterone, adrenaline

Question 20

Neurotransmitters (chemical nature, source, where it goes from the source, target cell(s), how it affects the TC, speed/longevity of the effect, examples)

Answer 20

can be amines, gases, amino acids, or esters, released by presynaptic neuron and travels across the synapse to the postsynaptic neuron, either excites or inhibits impulse transmission, has short-lived effects – e.g. acetylcholine, norepinephrine, dopamine

Question 21

Cytokines (chemical nature, source, where it goes from the source, target cell(s), how it affects the TC, speed/longevity of the effect, examples)

Answer 21

have the most profound effects on the cell out of all ligands – a group of small proteins secreted by a wide range of cells and affect that same cell or a nearby one by binding to its transmembrane receptors (hydrophilic) – can bind to different receptors on the same cell (different effects) – cause changes in gene expression and cell activity and have short-lives effects – e.g. erythropoietin (EPO), interferon, interleukin

Question 22

Roles of cytokines in the body

Answer 22

1| Inflammation and other immune system responses
2| Cell growth and proliferation control
3| Development of embryos

Question 23

Ca ions (source, where it goes from the source, target cell(s), how it affects the TC)

Answer 23

pumped out by calcium pumps and affect the same cell that pumped them out by diffusing through voltage/ligand-gated channels – cause presynaptic neurons to release neurotransmitters

Question 24

Roles of Ca ions in the body

Answer 24

1| Neurons - cause presynaptic neurons to release neurotransmitters into the synapse
2| Muscles - causes muscle fibers to contract

Question 25

G protein-coupled receptors (GPCRs)

Answer 25

a large and diverse group of transmembrane receptors which convey signals to cells using the G protein (a second protein located in the PM) made out of three subunits (alpha, beta, and gamma) and a GDP bound to the alpha subunit which keeps the G protein inactive

Question 26

How does signal transmission function with a GPCR

Answer 26

when a ligand binds, conformational changes are triggered in the receptor, which causes the disassembly of the G protein – GDP unbinds, turns into GTP (ADP phosphorylated to create ATP), and when GTP binds to the alpha subunit and activates the G protein – G protein separates into its subunits (alpha/beta-gamma) which then cause further interactions within the cell (bind to effector proteins in the membrane), leading to actions that are the cell’s response to the signal brought by the specific ligand

Question 27

Protein kinases

Answer 27

enzymes that transfers phosphate groups from ATP to proteins to activate them by phosphorylation, e.g. tyrosine kinase transfers phosphate to tyrosine in specific proteins

Question 28

Bioluminescence, which organisms can perform it, how is it formed?

Answer 28

metabolic processes in some organisms that produce light (biological light production)
bacteria (Vibrio fischeri), fungi, animals (marine vertebrates (jellyfish), fireflies, glowworms, lantern fish)
light is the byproduct of luciferin oxidation

Question 29

What are the purposes of bioluminescence?

Answer 29

1| Attracting prey and mates
2| Communication
3| Recognition
4| Evasion and scaring of predators
5| Providing light for symbiotic organisms
6| Attracting assistance in reproduction (mushrooms attracting insects)
7| Pigments to protect them from the sunlight (in more shallow waters)

Question 30

Quorum sensing

Answer 30

a process of cell-cell communication that allows single-celled organisms to share information about cell (population) density and adjust gene expression accordingly

Question 31

What are signaling molecules also called, what is their function?

Answer 31

autoinducers, the greater the population density the greater the concentration of the autoinducers, they bind to cell receptors and once the number of receptors bound with AI rises above the threshold gene expression gets induced

Question 32

Life cycle and its steps

Answer 32

a repetitive sequence of events between two cell divisions that enables cell proliferation (eukaryotes only) – interphase (G1, S, G2) and m-phase (mitosis (nuclear division of DNA) and cytokinesis (cytoplasm division)

Question 33

Interphase substeps

Answer 33

G1 (gap one): cell growth (chromosome DNA)
S: DNA replication/synthesis after it uncoiled, starting after a stimulus has been applied
G2: cell growth, preparation for cell division (increase in number of organelles, protein synthesis)

Question 34

Sister chromatids vs homologous chromosomes

Answer 34

chromatids made out of genetically identical DNA molecules (exact copies) – pairs of chromosomes in diploid organisms that have the same bending pattern/gene loci but can have different allelic forms of the same gene

Question 35

Outline what happens during each mitosis step

Answer 35

prophase: not completely condensed, double chromosomes (2n), nuclear envelope dissolves
metaphase: nuclear envelope gone, the completely condensed chromosomes align with the equator and are held in place by spindle microtubules
anaphase: chromosomes get pulled apart at the centromere by microtubules, from double to single (2n), travel to the opposite cell poles
telophase: chromosomes start uncoiling and nuclear envelope starts to reform, cleavage furrow appears

Question 36

Cytokinesis in plant vs animal cell

Answer 36

plant: vesicles containing plasma membrane components will accumulate and create two new plasma membranes and cell wall between them
animal: a cleavage furrow appears and divides the cell into two daughter cells (PM is more flexible than CW)

Question 37

How is mitotic index calculated and what is it used for?

Answer 37

(number of cells at any stage of mitosis)/(total number of cells)
comparing it with the “normal” MI for that tissue/age of the organism to see if there is a tumor (higher MI in that case) – stomach and skin are easily damaged so have a high normal MI while muscles, kidneys, and brain have zero because they cannot regenerate

Question 38

Checkpoints in the cell cycle and what they check

Answer 38

1| S-phase entry, if mitosis is complete, if the growth/protein synthesis in the cell is adequate, if there is DNA damage
2| Mitosis entry, if the DNA replication is complete, if the growth/protein synthesis in the cell is adequate, if there is DNA damage
3| Mitosis exit (before metaphase), checks if all chromosomes are attached to the spindles

Question 39

Cyclin proteins and different types

Answer 39

a family of proteins that ensure well-timed cell processes and cell division – their concentrations fluctuate in a specific pattern and each cyclin’s peak C is a trigger for a cell cycle phase
a cyclin needs to reach its C threshold level to bind to and activate kinase enzyme which will energize other molecules around it by phosphorylation and will thus, by increasing Ek, increase the number and rate of reactions responsible for specific tasks – cyclin D, E, A, and B

Question 40

What is apoptosis?

Answer 40

cell cell suicide or programmed cell death (lysosome role)

Question 41

What is a tumor?

Answer 41

a disease in which there is a defect in the regulation of the cell cycle (cells divide rapidly) caused by multiple gene mutations in cyclin genes

Question 42

What are two types of cyclin genes and what are their roles?

Answer 42

1| Proto-oncogenes code for proteins that promote division in a regulated manner
2| Tumor-suppressor genes prevent a mutated cell from dividing by coding for proteins that inhibit its division, fixing the mutation, or causing apoptosis (e.g. p53), they get triggered by DNA mutations

Question 43

What happens to each cyclin gene when it mutates, and what is the result of mutations of both genes?

Answer 43

proto-oncogenes will turn into oncogenes (their protein products do not perform their function properly and will stimulate the cell cycle in a non-regulated manner)
mutated tumor-suppressor genes will be unable to stop the mutated cell from dividing and a tumor will be formed

Question 44

What are mutagens?

Answer 44

factors that increase the incidence of mutations, e.g. radiation (UV and X-rays), cigarette smoke, and asbestos (lung inflammation)

Question 45

Types of tumors

Answer 45

primary tumor (initially formed) which can vary in rate of growth so can be benign (slow growth, cells tightly interconnected) and malignant (aggressive, invades neighboring tissues)
malignant can through metastasis (spreading of cells) form secondary tumors (life-threatening, in distant parts of the body)