Unit 1 Cell Theory

Question 1

What are the 7 basic functions essential for life to survive?

Answer 1

Mnemonic: MR SHENG
Metabolism – undertake essential chemical reactions

Reproduction – produce offspring, either sexually or asexually

Sensitivity – responsive to internal/external stimuli

Homeostasis – maintain a stable internal environment

Excretion – removal of waste products

Nutrition – exchange materials and gases with the environment

Growth – move and change shape or size

Question 2

What are the 3 rules to cell theory?

Answer 2

1. all living things are made of cells. (unicellular, multicellular)
2. new cells come from pre-existing cells.
3. The cell is the smallest unit of life. (cell division, zygote)

Question 3

What are 3 exceptions to cell theory?

Answer 3

1. striated muscle fibre: skeletal muscle is composed of muscle fibres, long fibres that measure 300mm or more. Surrounded by one, continuous plasma membrane
2. Aseptate fungi: contain many internal compartment-like structures called hyphae, which are separated into cells by internal walls called septa
   Some fungi are not partitioned, and thus have a continuous cytoplasm along the entire hyphae
   Challenges the idea that living structures are composed of distinct cells
3. Giant algae: unicellular organism that can grow up to 70+ mm in length
   Challenges idea that larger organisms are always made up of many microscopic cells

Question 4

What are the components of a eukaryotic cell?

Answer 4

Golgi Apparatus: Process and package proteins and lipid molecules into vesicles

Free Ribosomes: Synthesize proteins for inside the cell, 80s ribosomes, larger –> The ribosome reads the messenger RNA (mRNA) sequence and translates that genetic code into a specified string of amino acids, which grow into long chains that fold to form proteins.

smooth er: synthesizes lipids, metabolizes carbs, detoxifies poison, stores calcium

Rough Endoplasmic Reticulum (rER): Ribosomes secrete glycoproteins; protein (transport vesicles) production for outside-cell processes. (membrane factory)

Lysosomes: Digestive system

Nucleus: Hold the genetic DNA and chromatin, which is used for cell replication.

Mitochondria: Energy production (cellular respiration)

Plasma Membrane: Semi-permeable: manages what goes in and out of the cell.

Cytoplasm: Holds cell shape and organelles compartmentalized inside.

Cytoskeleton: network of fibers, organizes cell structure, activities, support

Question 5

What are the components of a prokaryotic cell?

Answer 5

Cell wall: Structure, support, protection

Plasma membrane: semi-permeable, chooses what goes in and out of organism

Cytoplasm: Enzymes used to catalyze, chem reactions, metabolism

Pili: Bacteria adhere to each other to transfer genetic material

Flagella: moves/propels bacteria

Ribosomes: 70s ribosomes; site of protein synthesis in the cell. The ribosome reads the messenger RNA (mRNA) sequence and translates that genetic code into a specified string of amino acids, which grow into long chains that fold to form proteins.

Nucleoid: Naked DNA

Question 6

Define emergent properties.

Answer 6

Properties that result when an entity interacts with other components in an organized structure (literally the whole is greater than the sum of its parts)

Question 7

Describe two key characteristics of stem cells that make them so versatile.

Answer 7

Self-renewal: able to undergo mitosis, while still remaining undifferentiated
Potency: able to specialize into a variety of cells

Question 8

Describe the five types of stem cells.

Answer 8

Totipotent (the very first cells formed following the fertilization of an egg cell): able to specialize into anything, as well as a zygote; very difficult to obtain
Pluripotent (e.g. embryonic stem cells of blastocyst): can form any cell type, except zygotes; sufficient for therapy
Induced pluripotent: same properties as pluripotent, but was artificially regressed from an adult stem cell
Multipotent, aka Adult (e.g. umbilical cord cells): can differentiate into a small number of closely related cell types; generally the most sought after to revert back to induced pluripotent
Unipotent: unable to differentiate, but is able to self-renew

Question 9

Describe two specific diseases that can be treated with stem cells.

Answer 9

Stargardt’s disease:
Juvenile macular degeneration that affects a small region near the center of the retina, causing progressive loss of central vision
Treated by injecting retinal cells that came from human embryonic stem cells

Leukemia:
Cancer of blood or bone marrow caused by high levels of abnormal white blood cells
Hematopoietic stem cells (HSC), a type of multipotent stem cells taken from the bone marrow, are transplanted back into bone marrow of patient after patient undergoes chemotherapy and radiotherapy to kill diseased WBC’ss
HSC’s specialize into new, healthy WBC’s

Question 10

Define a stem cell, and state a vital source of them.

Answer 10

An undifferentiated (nonspecialized) cell of a multicellular organism that can form more cells of the same type indefinitely, and is able to specialize into other kinds of cells

Embryos are a vital source of stem cells
Once an egg has been fertilized, it divides and forms totipotent cells during the early stages

Question 11

Explain the importance of a cell having a large SA:V ratio. Provide examples of optimizations found in the human body.

Answer 11

A small SA:V ratio results in the rate of resources entering/exiting the cell will not be sufficient to account for the cell’s comparatively massive volume
As a cell grows, its volume increases cubically but its SA only increases quadratically (slower)

E.g. the folds in the human brain increase SA:V ratio and allow more tissue to fit
Villi, or small folds on the inner lining of the small intestine help absorb nutrients more efficiently
- Even the villi have their own villi called microvilli

Question 12

Compare the life functions of paramecium to the life functions of chlamydomonas.

Answer 12

Paramecium
Metabolism: catalyzed by enzymes in cytoplasm
Reproduction: both asexual and sexual, though former is more common and occurs through binary fission
Sensitivity: moves cilia (hairs that aid movement) in wave-like action to respond to environmental changes
Homeostasis: contractile vacuoles collect excess water and expel it in order to maintain water balance - process is called osmoregulation
Excretion: waste products are transported from food vacuole in a vacuole to the anal pore, where it ruptures and excretes waste
Nutrition: engulfs food particles, where they are digested and their products absorbed into the cytoplasm
Growth: enlarges as it consumes food, and divides when large enough

Metabolism: catalyzed by enzymes in cytoplasm
Response: reproduces sexually and asexually
Sensitivity: senses light changes via eyespot and uses flagella to swim in response (e.g. to brighter area for better photosynthesis)
Homeostasis: contractile vacuoles collect excess water and expel it in order to maintain water balance - process is called osmoregulation
Excretion: uses whole surface of plasma membrane to excrete products
Nutrition: photosynthesis
Growth: enlarges as it photosynthesizes, divides into two daughter cells when large enough

Question 13

Describe the Davson-Danielli Model of the cell membrane.

Answer 13

Looked like a sandwich, where protein layers surrounded the phospholipid layer
Helped explain how membranes could be so thin yet maintain an effective semi-permeable layer
Accepted for 30 years until the Singer and Nicolson (Fluid Mosaic) Model was proposed

Question 14

Describe the Singer and Nicolson (Fluid Mosaic) Model of the cell membrane, as well as how the Davson-Danielli model was disproved.

Answer 14

Proposed that proteins are found at varying positions in the membrane
Two types of protein:
- Peripheral: attached to inner or outer surface
- Integral: protein was embedded and ran through the membrane

Falsification of Davson-Danielli:
Freeze-etched electron micrographs
- Flash froze membrane, ripped layers apart and looked at middle
- If it conformed to the Davson-Danielli model, it would be smooth; just lipid
- If it conformed to the Fluid Mosaic model, it would be bumpy as the proteins would be inconsistently placed
- The results concluded that the middle was bumpy, thus conforming to the Fluid Mosaic model

Structure of membrane proteins
- Proteins were extracted and analyzed to be seen in a variety of sizes as well as globular in structure
- Proteins were unlike the type that would form a smooth, continuous, flat layer as seen in Davson-Danielli’s model

Fluorescent Antibody Tagging
- Red and green markers were attached to membrane protein-binding antibodies
- Two cells were taken, had the antibodies attached to them and fused
- After about 40 minutes, red and green markers were mixed throughout the membrane of fused cells
- Proved that proteins were free to move with the membrane and came into regular contact (like in Fluid Mosaic model), rather than being forever separated by a phospholipid bilayer (as proposed by Davson-Danielli)

Question 15

Describe the structure of a lipid and phospholipid.

Answer 15

Lipid: one glycerol backbone with 3 attached hydrophobic fatty acids
Phospholipid: one glycerol backbone with a hydrophilic phosphate “head” and 2 attached hydrophobic fatty acid tails
Phospholipids are amphipathic

Question 16

Explain why phospholipids are used in a cell membrane.

Answer 16

Hydrophilic glycerol molecule and phosphate head mix well with water, facing outwards
Hydrophobic fatty acids pack together on the inside
The tight packing of the membrane disables most things from going through

Question 17

Describe the effects of cholesterol on the cell membrane.

Answer 17

Regulates cell speed:
If membrane is too hot, cholesterol acts as “speed bumps” to slow it down
If membrane is too cold, cholesterol acts to maintain fluidity

Question 18

State the six functions of membrane proteins.

Answer 18

Mnemonic: JETRAT
Junction: join and connect two cells
Enzyme: localize metabolic pathways
Transport: major role in facilitated diffusion (passive) and active transport
Recognition: May function as markers for identification
Anchorage: act as attachment points for cytoskeleton and extracellular matrix
Transduction: function as receptors for peptide hormones

Question 19

Describe the two types of passive transport, the driving force behind it and factors that affect the rate of it.

Answer 19

When molecules diffuse across the cell membrane on their own directly or through proteins; no energy required

Driving force: diffusion, the tendency for molecules to spread out evenly into available space through random movement; the movement of molecules down a concentration gradient

Types:
Simple diffusion
- Water and oxygen pass directly through membrane; small or hydrophobic molecules can do this
Facilitated diffusion
- Uses two types of protein: channel and carrier
- Channel acts as a tunnel, allowing a select few small-enough molecules to pass; nonspecific
- Allows smaller polar and smaller nonpolar molecules to cross
- Carrier protein opens to let larger molecules in, then closes, which opens the other side to let pass through the membrane; highly specific
- Allows larger polar and charged particles to cross

Factors:
Concentration gradient
- The larger the difference in concentration between concentrated area and non-concentrated area, the faster the rate of passive transport
Size of particles
- Larger particles are harder to move around
Temperature
- Cold –> slower
- Hot –> faster

Question 20

Define the three types of tonicity.

Answer 20

Hypotonic: solute concentration outside the cell is less than inside the cell
- Cell may burst as solvent (water) diffuses from outside to inside the cell in an attempt to equalize concentration
- Diffusion for water is called osmosis

Isotonic: solute concentration outside the cell is equal to inside the cell
- Cell remains healthy

Hypertonic: solute concentration outside the cell is more than inside the cell
- Cell may shrivel as solvent (water) diffuses from inside to outside the cell in an attempt to equalize concentration

Question 21

Describe the ATP cycle (how it gets recharged, where the water goes).

Answer 21

One “charged” ATP molecule consists of 3 phosphate groups
Releasing stored energy requires the use of water to “rip off” the third phosphate group (dephosphorylation)
The ATP has now turned into ADP and an inorganic phosphate group (Pi)
“Recharging” the ADP requires energy to form phosphorylate it with Pi, which in turn releases water to turn back into ATP

Question 22

Describe active transport, and state an example.

Answer 22

The movement of substances against (up) a concentration gradient, which requires energy that usually comes in the form of ATP
Allows cells to maintain a concentration gradient and avoid diffusion/osmosis
Example: sodium potassium pump (through membrane proteins), endocytosis, exocytosis (through vesicles)

Question 23

Describe the process of a sodium potassium pump.

Answer 23

Unpowered, the pump is open to the inside and closed to the outside
Three sodium ions bind to intracellular sites located inside the pump
An ATP transfers the sodium potassium pump its third phosphate group via condensation to provide it energy
The pump undergoes a conformational change to be closed to the inside and open to the outside
The three sodium ions leave to the outside
Two sodium molecules bind to intracellular sites inside the pump
The phosphate group is released, causing the pump to return to its original conformation
This translocates the potassium across the membrane into the cell, completing the ion exchange
Remember: Two K+ in - toucan!

Question 24

Describe bulk transport, and describe the two prominent types.

Answer 24

Bulk transport: taking in large molecules or large amounts of small molecules
Types:
Exocytosis (cell “excretion”)
- Transport vesicles migrate to the membrane, fuse with it and release contents
- Used to export products or dispel waste products

Endocytosis (cell “consumption”)
- Macromolecules arrive at the cell membrane, which forms a vesicle around contents to transport inside
Subtypes:
Phagocytosis (cell “eating”)
- The cell membrane “reaches out”, engulfs molecules and forms a vesicle for transportation
Pinocytosis (cell “drinking”)
- Extracellular fluid is “sipping” into tiny vesicles; the cell membrane does not “reach out”
Afterwards, vesicle goes towards endosome, which binds to lysosome to digest contents

Question 25

Describe the regulation of the cell cycle.

Answer 25

The cell cycle is regulated through proteins called cyclins that control the progress of cell production/division
A kinase is an enzyme that adds phosphates to molecules; phosphorylates molecules; a cyclin dependent kinase (CDK) is a kinase controlled by cyclin
When a cyclin and CDK bond, they form a complex that binds to a target protein and modify it via phosphorylation
The target protein, now phosphorylated, triggers a specific event in the cell cycle, such as duplicating chromosomes
After the event is finished, the cyclin degrades and the CDK goes back to inactive until reactivated by another cyclin
Different cyclins will bind to different classes of CDK
Cyclins are lettered:
D is used in G1 phase
E is used in S phase
A is used in G2 phase
B is used in mitosis

Question 26

Define abiogenesis, and describe Pasteur’s Experiment that proved biogenesis.

Answer 26

Abiogenesis: the (falsified) theory that living cells arose from nonliving matter
Biogenesis: the (proven) theory that living cells arise from preexisting cells

Pasteur’s test:
Nutrient-rich broth was boiled to kill any microorganisms (broth was sterilized)
Water condensed as the broth cooled, which sealed the flask
Bacteria did not grow in the broth unless the container’s seal was broken, proving cells cannot spontaneously occur and must arise from preexisting cells

Question 27

Describe Urey-Miller’s experiment of how simple organic molecules were first formed.

Answer 27

The conditions of Old Earth were simulated:
Water was boiled to vapour to reflect high temperatures
A reducing atmosphere was created when the water was mixed with gases such as H2, CH4, NH3, N2, but no free oxygen (no O2)
The mixture was exposed to electrical discharge to simulate the effects of lightning as an energy source for rections
The mixture was allowed to condense for a week
After this, the mixture was analyzed and discovered to contain traces of simple organic molecules (AA’s, carbs, lipids, etc.)

Proved that the basic building blocks of life could come from abiotic items
In the present day, Old Earth conditions no longer exist, thus cells must come from preexisting cells

Question 28

Describe endosymbiosis theory and the evidence that supports it.

Answer 28

Eukaryotic cells are believed to have evolved from early prokaryotes that were engulfed by phagocytosis (cell “eating”)
Engulfed prokaryote remained undigested as it provided new functionality to the devourer (such as photosynthesis)
Engulfed cell formed its own membrane, forming an endosymbiont: an organism that lives within the body of another, usually in a mutually-beneficial arrangement
Over time the engulfed cell became an organelle

Evidence:
Organelles that likely originated through endosymbiosis have the following characteristics:
Membranes: contain their own double layer membrane
Antibiotics: are vulnerable to antibiotics, suggesting a bacterial origin
DNA: have circular, naked DNA, similar to prokaryotes
Division: organelles divide through binary fission, similar to prokaryotes
Ribosomes: contain 70S ribosomes, just like prokaryotes

Question 29

Describe interphase of the cell cycle.

Answer 29

Most active and longest phase
Variety of processes: metabolism, endo/exocytosis, obtaining nutrients
Subphases:
G1
- Normal growth and function
- Proteins required for DNA synthesis/duplication are made
- Mitochondria replicate

S
- DNA replicates in preparation for mitosis
- Mitochondria continue to replicate

G2
- Proteins finish synthesizing and mitochondria finishing replicating

Question 30

Describe mitosis (excluding interphase and cytokinesis).

Answer 30

Prophase:
- DNA supercoils, condensing into chromatin
- Nucleolus and nuclear membrane disintegrates
- Spindle fibres made of microtubules start to form and finish forming at the end of prophase
- Centrioles (not in plant cells) move to opposite poles

Metaphase:
- Spindle fibres bind to each centromere of each pair of sister chromatids and move them to the equator
- By the end of metaphase, sister chromatids are all aligned

Anaphase (shortest phase):
- Sister chromatids are pulled apart by spindle fibres to opposite poles

Telophase:
- Sister chromatids (now called daughter chromosomes) reach poles
- Nuclear membrane reforms
- Nucleolus appears in each new nucleus
- Spindle fibres disintegrate

Question 31

Describe cytokinesis, and distinguish between cytokinesis in animal and plant cells.

Answer 31

Division of parental cytoplasm between two daughter cells after mitosis; often starts in telophase
Animal cells:
- Ring of protein (microfilaments) pulls plasma membrane inwards at equator
- A cleavage furrow is formed (space between cells)
- When the cleavage furrow reaches the center of the cells, the two cells are pinched apart to form two daughter cells

Plant cells:
- Golgi apparatus forms vesicles that consist of materials to build up a new cell wall
- Vesicles merge and form a new cell plate, which grows in between and divides the two daughter cells

Question 32

Define turmourigenesis and describe tumours.

Answer 32

Tumourigenesis: formation of a, or several tumours
A tumour is a mass of cells that uncontrollably divide
Types of tumours:
Benign
- Localized, do not spread to other parts of body
- Respond well to treatment
Malignant
- Cancerous growth that often resists treatment
- May spread to other parts of body and recur after removal

The mutation of a single cell or gene can result in tumour formation

Question 33

Define oncogenes, primary and secondary tumours.

Answer 33

Oncogene: a mutated gene that contributes to the development of a tumour
When not mutated, they are called proto-oncogenes, which assist in regulating cell division

Primary tumour: the tumour formed at the point of origin, where the mutation occurred
Secondary tumour: when primary tumours metastasize, or more away from origin

Question 34

Describe compound light microscopes, transmission electron microscopes and scanning electron microscopes.

Answer 34

Compound light microscope:
Light travels though several glass lens to view specimen
Takes minutes to prepare
Specimen can be live or dead
Only cells and large organelles can be viewed; nothing smaller
Resolving power is 0.2 micrometers
Image is 2D, coloured

TEM:
Image is produced by electrons manipulated with magnets and viewed on a fluorescent screen
Image cannot be in colour and is 2D

SEM:
Image is produced by electrons manipulated by magnets and viewed on a monitor
Resolving power (smallest image) is 0.001 micrometers, 200x stronger than a compound light microscope
Ultrastructure of cells could now be seen
Image cannot be in colour but is be 3D