Cellular structure/processes

Question 1

What the cell structure basics

Answer 1

basic structural, biological, functional units that comprises an organism

Smallest self-replicating life-form

Question 2

The main levels of organization in the body, from the simplest to the most complex are:

Answer 2

Cells > tissues > organ > organ system > organism

Question 3

What are the basic constituents of cells

Answer 3

• Plasma membrane
  
  • Cytoplasm: everything in cell membrane except nucleus)
• Fluid suspension
  
  • Composition: cytosol (liquid found inside of cells), organelles

Question 4

What is the Cytosol?

Answer 4

Intracellular fluid

• Composition: dissolved/suspended organic, inorganic chemicals; macromolecules; pigments; organelles are in the cytosol
  
  • the cytosol is the fluid surrounding it.
• Site of most cellular activity.

Question 5

Where is the site of most cellular activity?

Answer 5

The Cytosol (in cytoplasm)

Site of most cellular activity

Question 6

What is the composition of ribosomes?

Answer 6

rRNA, ribosomal proteins

Question 7

Where can you find ribosomes

Answer 7

Can exist freely in the cytoplasm/bound to endoplasmic reticulum (forms rough endoplasmic reticulum)

Question 8

What is the purpose of ribosomes

Answer 8

Turns mRNA into protein via translation

Question 9

What subunits are ribosomes organised into?

Answer 9

• Organized into two subunits (40’s, 60’s)
  
  • Small subunit: binding sites for mRNA, tRNA
  • Larger subunit: has ribosome to catalyse peptide bond formation (for bonds between amino acids)

Question 10

What is the endoplasmic reticulum?

Also, what is its appearance?

Answer 10

membrane-enclosed organelle

Appearance: a stack of membranous. Flattened disks (cisterns)

Question 11

Rough endoplasmic reticulum (RER) structure

Answer 11

Contain bound ribosomes on the surface

Rough endoplasmic reticulum cisterna continuous with nuclear envelope.

Question 12

What is the function of Rough endoplasmic reticulum

Answer 12

Site of packaging, folding of proteins Designated for secretion, lysosomal degradation,
plasma membrane insertion, proteins packed into vesicles, sent to Golgi apparatus for further modification

Question 13

Smooth endoplasmic reticulum structure

Answer 13

No ribosomes

Question 14

Smooth endoplasmic reticulum function

Answer 14

Site of making lipids, steroid synthesis (Glans), ions storage (muscles), glycogen metabolism, Detoxification (liver).

Question 15

Golgi apparatus purpose/function

Answer 15

Golgi apparatus

Post-translational modification site (e.g. phosphorylation, glycosylation, sulfonation) of proteins, lipids hormones
→ sorted, packed into secretory vesicles → secreted out of cell/lysosomal fusion/plasma membrane insertion

Question 16

Golgi apparatus Structure

Answer 16

Membrane-enclosed organelle

Appearance: a collection of fused, flattened sacs (cisterns) with associated vesicles, vacuoles

Two sides

Cis-side: receives proteins from Rough endoplasmic reticulum (entry)

Trans side: opposite side, releases vesicles towards the plasma membrane (Exit)

Question 17

what are the Golgi apparatus side(s) functions

Answer 17

Two sides

Cis-side: receives proteins from Rough endoplasmic reticulum (entry)

Trans side: opposite side, releases vesicles towards the plasma membrane (Exit)

Question 18

Mitochondria Structure

Answer 18

Double membrane-enclosed organelle;

Outer smooth membrane: Inner membrane:

Inner membrane space: space between the inner, outer membrane

Question 19

Mitochondria Purpose

Answer 19

synthesizes ATP for cell via aerobic respiration

In cytoplasm glucose undergoes glycolysis, glucose is cleaved into pyruvate.

Pyruvate enters mitochondria > citric acid cycle (Krebs cycle), electron transport chain (which require oxygen)

In glucose absence, mitochondria can use fatty acids as fuel via beta-oxidation (only medium-sized fatty acids used; longer ones chopped by peroxisome)

Mitochondria number: correlates with cell activity/energy/requirements.

Question 20

Nucleus Structure

Answer 20

Large, membrane-enclosed organelle present in all cells except mature erythrocytes (RBC)

Most cells contain one nucleus; some cells have more (e.g. muscle cells, osteoclasts, hepatocytes)

Usually spherical, may take on other shapes

Lobulated (e.g. polymorphonuclear leukocytes)

Elongates (e.g. columnar epithelium)

Question 21

Nucleus purpose

Answer 21

Contains genetic material (DNA, tightly packed into chromatin); coordinates cellular activities

Question 22

Cell membrane structure

Answer 22

Semipermeable membrane made from phospholipid bilayer; surrounds cell cytoplasm

Question 23

Cell membrane: phospholipid bilayer structure

Answer 23

Two-layered polar phospholipid molecules comprising two parts

Negatively charged phosphate “head” (hydrophilic; orientated outwards)

Fatty acid “tail” (hydrophobic orientated (inwards)-

Question 24

why is the phospholipid layer Semipermeable?

Answer 24

Allows passage of certain molecules through the membrane (0₂, C0₂ etc)

Denies passage of others (large molecules such as proteins, glucose)

Certain molecule transportation (Ions, H₂O) allowed through embedded membrane proteins (ion channels, pumps)

Question 25

What is meant by "Selective permeability of the cell membrane"

Answer 25

**Cell membrane controls which molecules enter and leave:** Passive transport: Active transport: energy is required

Question 26

In relation to energy, What is passive transport?

Answer 26

Passive transport: no energy required to pass cell membrane

Question 27

In relation to energy, What is Active transport:

Answer 27

Active transport: energy is required to cross cell membrane = adenosine triphosphate (ATP)

Question 28

Explain passive transport

Answer 28

Simple diffusion Random molecular motion Small nonpolar molecules move from high concentration -\> low concentration

Question 29

What affects diffuse flux (Ficks law)

Answer 29

**_Three factors_** **Concentration gradient** * Larger differences in solute concentration on each side of the membrane -\> high driving force -\> high net diffusion * Equal concentrations -\> no net diffusion (e.g. , movement between alveoli and blood) **Membrane surface area** * Increase surface area available for diffusion -\> increase diffusion rate; vice versa (e.g. microvilli in small intestines amplify the surface area -\> increase nutrient, water distribution) **The distance separating each side of the membrane (e.g. thickness)** * Increase distance molecules must travel -\> decrease of net diffusion; vice versa (e.g. pulmonary oedema -\> increase distance between compartments -\> decrease net diffusion)

Question 30

How does concentration affect diffuse flux? (Ficks Law)

Answer 30

**Concentration gradient** Larger differences in solute concentration on each side of the membrane -\> high driving force -\> high net diffusion Equal concentrations → no net diffusion (e.g. , movement between alveoli and blood)

Question 31

How does membrane surface area affect diffuse flux (Ficks law)

Answer 31

**Membrane surface area** Increase surface area available for diffusion -\> increase diffusion rate; vice versa (e.g. microvilli in small intestines amplify the surface area -\> increase nutrient, water distribution)

Question 32

How does The distance separating each side of the membrane affect diffuse flux (Ficks law)

Answer 32

**_The distance separating each side of the membrane (e.g. thickness)_** Increase distance molecules must travel -\> decrease of net diffusion; vice versa (e.g. pulmonary oedema -\> increase distance between compartments -\> decrease net diffusion)

Question 33

What is Facilitated diffusion?

Answer 33

Uses transport proteins (e.g. channels, carrier proteins) Allows larger/polar molecules to move across the membrane

Question 34

What are Channels on the cell membrane?

Answer 34

Non-specific, open to allow water, small polar molecules through (e.g. voltage-gated calcium channel)

Question 35

What are Carrier proteins on cell membranes

Answer 35

Very specific, only allow certain molecules to bind (e.g. glucose transporter (GLUT4)

Question 36

Explain primary active transport

Answer 36

**_Primary_** Uses ATP Enzymes called ATPases use ATP as fuel; (e.g. Na+/K+-ATPase, ATPase, H⁺/K⁺ ATPase) May _create_ concentration/electrochemical gradients

Question 37

Explain secondary active transport

Answer 37

**Secondary** Uses existing electrochemical gradients One solute, normally Na+ moves with concentration gradient through transporter -\> supplies energy transporter needs to -\> another solute against concentration gradient in same/opposite direction as Na+ (e.g. sodium-glucose SGLT1 transporter)

Question 38

Explain Bulk transport

Answer 38

**AKA vesicular transport** _Endocytosis_ Cell membrane invaginates, pulling something in from outside e.g. pathogen phagocytosis) _Exocytosis_ Vesicle inside cell pushes something (e.g. hormone secretion)

Question 39

What is the Extracellular Matrix

Answer 39

The environment surrounding the cells Varies between tissues (epithelial, connective, and nervous)

Question 40

What are the major molecules in the extracellular matrix?

Answer 40

Adhesive proteins Structural proteins Proteoglycans

Question 41

What are Adhesive proteins

Answer 41

Adhere cells together (communication with extracellular fluid) e.g. integrating cadherins

Question 42

What is the purpose of Structural proteins?

Answer 42

* Give tissues tensile, compressive strength * Collagen * Resists tension, can stretch * Starts as procollagen → cleaves into tropocollagen → arranged into fibrils * Four major types of structural proteins: type 1(bone, skin, tendon). Type 2 (cartilage), type 3 (reticulin, blood vessels), Type 4 (basement membrane) * Elastin * Elastic, returns tissue to original shape * Keratin * Tough, found in hair and nails

Question 43

What are Proteoglycans?

Answer 43

Fill space between cells, hydrate, cushion cells Consists of a protein core with sugar chains

Question 44

What is the purpose of Cell-Cell junctions

Answer 44

Protein structures that physically connect cells Improve cellular communication, tissue structure; allow transport of some substances between cells, create an impermeable barrier for others Only found between immobile cells; abundant in epithelial tissue (e.g. in the skin)

Question 45

What are the three junction types?

Answer 45

Tight junctions Adherens junctions Gap junctions

Question 46

What are Tight junctions?

Answer 46

e.g. in the gastrointestinal tract/brain Seal adjacent-cell plasma membranes, especially near the apical surface; prevent the passage of water. Small proteins, bacteria Formed by claudins, occluding embedded in cellular plasma membranes In "leaky" epithelia, tight junctions may allow certain molecules to pass (e.g. K+. Na+, -CL in kidneys proximal tubules - due to ion pores)

Question 47

What are Adherens junctions?

Answer 47

e.g. in skin Anchor cells together, provide strength; consist of three major components Actin filaments: provide cellular shape Protein plaques: anchor membrane bind to actin filaments Cadherins: attach to protein plaques, connect to cadherins on other cells.

Question 48

What are Gap junctions?

Answer 48

E.g. in heart Connect adjacent cells, allow rapid communication; formed by connexins -\> create tubular structure (allows charged particles to pass) **In cardiac myocytes:** gap junctions create coordinated heart contractions **In infected cells:** gap junctions send cytokines to neighbouring cells, triggering apoptosis, preventing infectious spread ("bystander effect")

Question 49

Endocytosis and exocytosis

Answer 49

ransports material in/out of cell Requires adenosine triphosphate (ATP) for energy

Question 50

What does endocytosis do? Three types are:

Answer 50

Cell engulf extracellular material Three types are: phagocytosis, pinocytosis & receptor-mediated endocytosis

Question 51

What does phagocytosis do?

Answer 51

Aka cell eating Used by white blood cells (e.g. macrophages, neutrophils) **Process:** * The cell extends arm-like projects (AKA pseudopods) around the target * Cell membrane slowly engulfs target, invaginates to form a vesicle * Vesicle separates from cell membrane to form a phagosome * Phagosome fuses with lysosome, target is digested * Debris released by exocytosis

Question 52

What is pinocytosis

Answer 52

Aka cell drinking Edges of invagination come together to form a vesicle Motor proteins use ATP to carry vesicles into the cytosol

Question 53

What is receptor-mediated endocytosis?

Answer 53

Used by cells to take in specific molecules (e.g. iron, cholesterol) **Process** * Clathrin-covered pits/coated pits with receptors bind certain molecules * Edges of put come together, clathrin proteins link up * Vesicle pinches off; clathrin detaches, return to the cell membrane * Vesicle merges with endosome to separate receptors into the second vesicle

Question 54

What is Exocytosis?

Answer 54

Cells expel material into extracellular space (e.g. neurotransmitters, hormone) Last phagocytosis step Process * Golgi apparatus creates vesicle from various proteins, lipids, hormones * Motor proteins use ATP to carry vesicle along cytoskeleton * Vesicle pressed against cell membrane until rupture -\> spills contents into extracellular space.

Question 55

What is Osmosis?

Answer 55

Passive water-flow across selectively permeable (semipermeable) cellular membrane; primarily determined by solute concentration differences (osmotic pressure)

Question 56

Factors affecting water movement across the membrane?

Answer 56

* Molecules (e.g. water molecules, ions) tend to move around kinetic energy) + movement is disordered, random (entropy) → larger solutes tend to block openings in a semipermeable membrane * If solute ions positively charged, they attract slightly negatively charged oxygen atoms in water molecule; if solute ions are negatively charged they attract slightly positively charged hydrogen atoms in water molecule → water molecules partially attached to the ion → movement through membrane impeded * Water molecules tend to move from hypotonic side (more water/less solutes) to hypertonic side (less water/more solute)

Question 57

What relation does the selectively permeable membrane have on Osmosis?

Answer 57

Allows small molecules (e.g. water) across, but not larger molecules/ions

Question 58

In an isotonic solution..

Answer 58

Side A= Side B If solute concentration is the same on each side of membrane -\> net water movement across membrane is zero (equilibrium)

Question 59

In Hypertonic/hypotonic solution....

Answer 59

Side a\> side B or Side B \>Side A If the solute concentration is greater on one side (hypertonic) -\> net water migration across the membrane is from the hypotonic side toward the hypertonic side

Question 60

Cellular effects on hypertonic, hypotonic solution

Answer 60

Red blood cells in **hypertonic solution** → net movement of water molecules out of cell → cell shrinks (cremation) Red blood cell in **hypotonic solution**→ net movement of water molecules into cell → cell swells may burst (lyses)

Question 61

Resting membrane potential: Electric potential across cell membrane

Answer 61

* Given weighted (based on membrane permeability) sum of equilibrium potentials for all ions. * High concentrations of Na+, -Cl, Ca+ outside the cell; high concentrations of k+, -A (various anions) inside cell -\> concentration gradients are established Sodium-potassium pump uses ATP to move two K+ ions into cell, three Na+ ions out. * Potassium concentration = 150mMol/L inside cell, 5mMol/L outside cell.

Question 62

Resting membrane potential: Concentration gradients

Answer 62

Concentration gradients establish electrostatic gradients * Concentration gradient pushes potassium out through potassium leaky channels, inward rectifier channels * Anions remain in cells -\> negative charge builds up -\> potassium is pulled back into cell.

Question 63

Resting membrane potential: Equilibrium (Nernst) potential:

Answer 63

Equilibrium (Nernst) potential: electrostatic gradient equal to concentration gradient (-92mV for potassium) Value is flipped for negative ions Resting membrane potential is sum of equilibrium potentials of major ions multiplied by their membrane permeabilities.

Question 64

Cell signalling pathway stages

Answer 64

Cell signalling pathway stages * **Reception**: ligand binds to receptor * **Transduction:** receptor changes activating intracellular molecules * **Response:** signal triggers a response in target cell

Question 65

Ion channel receptors

Answer 65

Ion channels that open specific ligands bind Allow ions (e.g. chloride, calcium, sodium, potassium) to flow through The resulting shift in electrical charge distribution triggers a response

Question 66

cytoskeleton & intracellular motility

Answer 66

Non-membrane bound organelles comprising complex protein filament network Provide structural stability, shape, organisation, intracytoplasmic motility, cell motility

Question 67

Cytoskeleton protein filament network Types

Answer 67

Microfilaments Microtubules Intermediate filaments

Question 68

Nuclear Envelope

Answer 68

* Encloses separates the nucleus from the cytoplasm * Composed of the selectively permeable membrane phospholipid bilayer Consists of: * Nuclear pores * Outer membrane * Inner membrane

Question 69

Nuclear pores:

Answer 69

* Form where membranes fuse together at various intervals * Each pore is lined with a nuclear pore complex (nucleoporin) to facilitate communication between the nucleus, cytoplasm * Allow bidirectional macromolecule movement

Question 70

Outer membrane

Answer 70

Anchoring proteins that hold nucleus in place with cytoplasm Continuous with rough endoplasmic reticulum

Question 71

Inner membrane

Answer 71

Covered by the nuclear lamina Thin filamentous protein network, creates web within the nucleus; provide support for chromatin

Question 72

Nucleosome

Answer 72

Eight histones packed together in four stacks of two; DNA wraps around them twice Strung on strand of DNA-like "beads on string"

Question 73

Two chromatin types

Answer 73

Euchromatin: loosely packed DNA, actively being transcribed into RNA Heterochromatin: densely packed DNA, inactive (not being transcribed)

Question 74

Nucleolus

Answer 74

* Dense non-membrane-bound structure; some cells have more than one nucleolus * Contains rDNA -\> transcribes into rRNA * Assembles ribosomal subunits

Question 75

Nucleoplasm

Answer 75

* Protoplasmic material * Composed of complex water, molecule, ion mixture * Contains nucleolus, chromatin

Question 76

Chromatin

Answer 76

* Helical fibre * Composed of 46 DNA molecules wrapped around proteins (histones) * Histones help regulate DNA, gene expression * Chromosomes become visible as chromatin fibres become tightly coiled during cellular division