IB Biology Topic 1

Totipotent

Stem cell type, present in morula, can become any human cell and placenta

Pluripotent

Stem cell type, inner cell mass, can become any human cell

Multipotent

Stem cell type, can become a few closely-related types of cell

Unipotent

Stem cell type, regenerate, can only become their associated cell type

Regenerative Medicine: Leukaemia

* Hematopoietic Stem Cells → Bone marrow stem cells that circulate in the blood stream


* Leukaemia → White blood cells mutate and stop functioning
* Stem Cell Therapy → Chemo/Radiation destroy malfunctioning leukocytes and bone marrow stem cells, replace with healthy hematopoietic stem cells from matching donor

Regenerative Medicine: Stargardt’s Disease

* Inherited macular(photoreceptor) degeneration causing central vision loss


* Stem Cell Therapy → Embryonic stem cells are used to produce Retinal Pigment Epithelial cells to slow or stop photoreceptor loss

Stem Cell Source: Embryonic

Advantages

* Can be obtained from excess IVF embryos
* Almost unlimited growth potential + pluripotent
* Less chance of genetic damage

Disadvantages

* Embryo destruction
* Higher risk of tumour development
* Not genetically identical to patient

Stem Cell Source: Umbilical

Advantages

* Umbilical cord discarded
* Easily obtained and stored 
* Unlikely to develop into tumour + less genetic damage
* Genetically identical to patient

Disadvantages

* Limited quantities available
* Reduced growth potential
* Limited capacity to differentiate(only blood cells unless induced)

Stem Cell Source: Adult Somatic

Advantages

* Adult patient can give consent
* Unlikely to develop into tumour
* Genetically identical to patient

Disadvantages

* Reduced growth potential
* Difficult to obtain
* Multipotent unless induced
* Genetic damage can occur

Resolution + Electron Microscopes

Shortest distance between two points that can be distinguished

Better resolution than light microscopes(200nm vs 1nm) as light waves are too large to fit through smaller gaps, can see organelles

Ultrastucture

All structures of a biological specimen that are ≥0.1nm in their smallest dimension

Binary Fission

* DNA replicated semi-conservatively


* 2 DNA loops attach to the membrane 
* Membrane elongates and pinches off(cytokinesis)
* Asexual, produces two identical daughter cells

Compartmentalisation Benefits

* Efficiency of metabolism → substrates and enzymes can be localised and concentrated


* Localised conditions → pH etc. can be kept at differents levels
* Toxic/damaging substances can be isolated → digestive enzymes stored in lysosomes
* Numbers and locations of organelles can be changed based on cell requirements

Generalised Animal Cell(7)

* Vesicle
* Lysosome
* Nucleus
* Rough Endoplasmic Reticulum
* Golgi Apparatus
* Ribosomes
* Mitochondrion

Generalised Plant Cell(9)

* Nucleus
* Rough Endoplasmic Reticulum
* Golgi Apparatus
* Ribosomes
* Mitochondrion
* Vacuole
* Cell Membrane
* Cell Wall
* Chloroplast

Davson-Danielli Model

Proposed membrane ‘sandwich’ of phospholipids inside proteins, falsified

Issues:

* Freeze-etching → freeze sample then cut to reveal irregular surfaces and transmembrane proteins
* Structure of membrane proteins → Membrane proteins were discovered to be insoluble in water and varied in size, not able to form a uniform and continuous layer around the outer surface of a membrane
* Fluorescent antibody tagging → showed they were mobile and not fixed in place, demonstrated that the membrane proteins could move and did not form a static layer

Membrane Proteins(9)

Proteins embedded either permanently or temporarily in the membrane

Types:

* Integral Proteins → permanently attached, typically span the bilayer
* Peripheral Proteins → temporarily attached by non-covalent interactions, associate with one surface of the membrane
* Junctions → Connect cells together
* Enzymes → Catalyse reactions at the membrane level, localise metabolic pathways
* Active Transport → Carriers, bind to substances on one side of the membrane then change shape to transport them to the other side, protein pumps
* Passive Transport → Channels, some proteins have a pore/channel that allows passive transport of substances
* Cell to Cell Recognition → Certain proteins help the cell in recognising the difference between itself and other cells, important for immune response
* Anchorage → Attachment points for cytoskeleton and extracellular matrix
* Receptors → Proteins that extend through the cell membrane to send information into or out of the cell

Cholesterol in the Membrane

Regulates fluidity and flexibility of the membrane based on temperature

Fluid-Mosaic Model

Singer-Nicholson

Membrane Transport: Simple Diffusion

* Down conc. gradient
* A concentration gradient, small non-polar molecules
* Oxygen, carbon dioxide

Membrane Transport: Facilitated Diffusion

* Down conc. gradient
* Concentration gradient, transmembrane proteins, large polar molecules
* Oxygen in blood, glucose

Membrane Transport: Osmosis

* Area of low solute concentration to high solute concentration
* Concentration gradient, aquaporin (both simple + facilitated)
* Exclusively water

Membrane Transport: Active Transport

* Against conc. gradient
* Integral protein pumps, ATP
* Sodium-potassium pumps

Membrane Transport: Endocytosis

* Out of cell
* Inward pouching of plasma membrane, forming a vesicle

Membrane Transport: Exocytosis

* Into cell
* Vesicle joins plasma membrane, releasing contents

Isotonic

Same osmolarity, no change to tissues in these solutions

Hypertonic

Higher osmolarity, tissue would become dehydrated

Hypotonic

Lower osmolarity, tissue would have increased turgor pressure

Sodium-Potassium Pump

Active Transport and Facilitated Diffusion


1. Three sodium ions bind to intracellular sites on the pump
2. A phosphate group is transferred to the pump via the hydrolysis of ATP
3. The pump undergoes a conformational change, moving sodium out of cell
4. Two potassium binding sites are exposed on the extracellular surface
5. The phosphate group is released, pump returns to its original conformation
6. Potassium moves into cell