Cellular structure/processes Flashcards
What the cell structure basics
basic structural, biological, functional units that comprises an organism
Smallest self-replicating life-form
The main levels of organization in the body, from the simplest to the most complex are:
Cells > tissues > organ > organ system > organism
What are the basic constituents of cells
- Plasma membrane
- Cytoplasm: everything in cell membrane except nucleus)
- Fluid suspension
- Composition: cytosol (liquid found inside of cells), organelles
What is the Cytosol?
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.
Where is the site of most cellular activity?
The Cytosol (in cytoplasm)
Site of most cellular activity
What is the composition of ribosomes?
rRNA, ribosomal proteins
Where can you find ribosomes
Can exist freely in the cytoplasm/bound to endoplasmic reticulum (forms rough endoplasmic reticulum)
What is the purpose of ribosomes
Turns mRNA into protein via translation
What subunits are ribosomes organised into?
- 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)
What is the endoplasmic reticulum?
Also, what is its appearance?
membrane-enclosed organelle
Appearance: a stack of membranous. Flattened disks (cisterns)
Rough endoplasmic reticulum (RER) structure
Contain bound ribosomes on the surface
Rough endoplasmic reticulum cisterna continuous with nuclear envelope.
What is the function of Rough endoplasmic reticulum
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
Smooth endoplasmic reticulum structure
No ribosomes
Smooth endoplasmic reticulum function
Site of making lipids, steroid synthesis (Glans), ions storage (muscles), glycogen metabolism, Detoxification (liver).
Golgi apparatus purpose/function
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
Golgi apparatus Structure
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)
what are the Golgi apparatus side(s) functions
Two sides
Cis-side: receives proteins from Rough endoplasmic reticulum (entry)
Trans side: opposite side, releases vesicles towards the plasma membrane (Exit)
Mitochondria Structure
Double membrane-enclosed organelle;
Outer smooth membrane: Inner membrane:
Inner membrane space: space between the inner, outer membrane
Mitochondria Purpose
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.
Nucleus Structure
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)
Nucleus purpose
Contains genetic material (DNA, tightly packed into chromatin); coordinates cellular activities
Cell membrane structure
Semipermeable membrane made from phospholipid bilayer; surrounds cell cytoplasm
Cell membrane: phospholipid bilayer structure
Two-layered polar phospholipid molecules comprising two parts
Negatively charged phosphate “head” (hydrophilic; orientated outwards)
Fatty acid “tail” (hydrophobic orientated (inwards)-
why is the phospholipid layer Semipermeable?
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)
What is meant by “Selective permeability of the cell membrane”
Cell membrane controls which molecules enter and leave:
Passive transport:
Active transport: energy is required
In relation to energy, What is passive transport?
Passive transport: no energy required to pass cell membrane
In relation to energy, What is Active transport:
Active transport: energy is required to cross cell membrane = adenosine triphosphate (ATP)
Explain passive transport
Simple diffusion
Random molecular motion
Small nonpolar molecules move from high concentration -> low concentration
What affects diffuse flux (Ficks law)
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)
How does concentration affect diffuse flux? (Ficks Law)
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)
Explain Bulk transport
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)
What are Adhesive proteins
Adhere cells together (communication with extracellular fluid)
e.g. integrating cadherins
What is the purpose of Structural proteins?
- 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
What are Proteoglycans?
Fill space between cells, hydrate, cushion cells
Consists of a protein core with sugar chains
What are the three junction types?
Tight junctions
Adherens junctions
Gap junctions
What does endocytosis do?
Three types are:
Cell engulf extracellular material
Three types are: phagocytosis, pinocytosis & receptor-mediated endocytosis
What does phagocytosis do?
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
What is pinocytosis
Aka cell drinking
Edges of invagination come together to form a vesicle
Motor proteins use ATP to carry vesicles into the cytosol
What is receptor-mediated endocytosis?
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
What is Exocytosis?
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.
In an isotonic solution..
Side A= Side B
If solute concentration is the same on each side of membrane -> net water movement across membrane is zero (equilibrium)
In Hypertonic/hypotonic solution….
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
Resting membrane potential: Electric potential across cell membrane
- 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.
Resting membrane potential: Concentration gradients
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.
Resting membrane potential: Equilibrium (Nernst) potential:
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.
Nuclear pores:
- 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
Outer membrane
Anchoring proteins that hold nucleus in place with cytoplasm
Continuous with rough endoplasmic reticulum
Inner membrane
Covered by the nuclear lamina
Thin filamentous protein network, creates web within the nucleus; provide support for chromatin
Nucleosome
Eight histones packed together in four stacks of two; DNA wraps around them twice
Strung on strand of DNA-like “beads on string”
Two chromatin types
Euchromatin: loosely packed DNA, actively being transcribed into RNA
Heterochromatin: densely packed DNA, inactive (not being transcribed)
