Topic 1 - Cell Biology Flashcards
Understand Cell Biology or die.
Cell Theory
- All living things are composed of cells (or cell products)
- The cell is the smallest unit of life
- Cells only arise from pre-existing cells
Exceptions to Cell Theory
Striated Muscle Cells
Acetate Fungal Hyphae
Giant Algae
Striated Muscle
Long Cells, (300 mm), multiple nuclei, questions cell theory.
Acetate Fungal Hyphae
challenges idea that cell is a single unit, multi-nucleated, and continuous cytoplasm. Cell walls composed of Chitin
Giant Algae
challenges that notion that cells must be small, and simple in structure. Size of 5-100mm and complex in form.
What can Living Organisms do?
Response, Grow, Homeostasis, Reproduce, Excrete and Nutrition.
SA:Volume
A larger SA:Vol ratio can mean that a cell can act more efficiently. For every unit of volume that requires nutrients or produces waste. There is more membrane to serve it
Rate of Metabolism
Mass/Volume
Emergent Properties
Emergent properties arise when the interaction of individual component produce new functions
Specialised cells
All specialized cell and the organs constructed are from differentiation
Stem Cells
unspecialized cells that can differentiate into many cell types
- Self Renewal – They can continuously divide and replicate
- Potency – They have the capacity to differentiate into specialised cell types
Totipotent
Can differentiate into any cell
Pluripotent
Can differentiate into many cells
Multipotent
Can differentiate into a few closely related cells
Unipotent
Can regenerate,but only into associated cell type
Magnification Calculation
Magnification = Image size (with ruler) ÷ Actual size (according to scale bar)
Use of stem cells
stem cells have become a viable therapeutic option when these tissues that tissues cannot be regenerated become damaged.
Stargardt’s Disease
- An inherited form of juvenile macular degeneration that causes progressive vision loss to the point of blindness
- Caused by a gene mutation that impairs energy transport in retinal photoreceptor cells, causing them to degenerate
- Treated by replacing dead cells in the retina with functioning ones derived from stem cells
Parkinson’s Disease
- A degenerative disorder of the central nervous system caused by the death of dopamine-secreting cells in the midbrain
- Dopamine is a neurotransmitter responsible for transmitting signals involved in the production of smooth, purposeful movements
- Consequently, individuals with Parkinson’s disease typically exhibit tremors, rigidity, slowness of movement and postural instability
- Treated by replacing dead nerve cells with living, dopamine-producing ones
Leukemia
Bone marrow transplants for cancer patients who are immunocompromised as a result of chemotherapy
Hematopoietic Stem Cells (HSCs) are harvested from bone marrow, peripheral blood or umbilical cord blood
Chemotherapy and radiotherapy used to destroy the diseased white blood cells New white blood cells need to be replaced with healthy cells. HSCs are transplanted back into the bone marrow HSCs differentiate to form new healthy white blood cells
Paraplegia
Repair damage caused by spinal injuries to enable paralysed victims to regain movement
Diabetes
Replace non-functioning islet cells with those capable of producing insulin in type I diabetics
Burn victims
Graft new skin cells to replace damaged tissue
Obtaining Stem Cells
Embryos (may be specially created by therapeutic cloning)
Umbilical cord blood or placenta of a new-born baby
Certain adult tissues like the bone marrow (cells are not pluripotent)
Ethical considerations of Stem Cells
Using multipotent adult tissue may be effective for certain conditions, but is limited in its scope of application
Stem cells derived from umbilical cord blood need to be stored and preserved at cost, raising issues of availability and access
The greatest yield of pluripotent stem cells comes from embryos, but requires the destruction of a potential living organism
Artificial Stem Cell Techniques
Somatic cell nuclear transfer (SCNT)
Nuclear reprogramming
Prokaryote Cell
no nucleus, approx. 0.5 μm
Can be Archaebacteria (i.e. extremophiles) or Eubacteria (e.g. E. coli, S. aureus, etc.)
Prokaryotic Reproduction
Asexually through binary fission.
Steps of Binary Fission
- The circular DNA is copied in response to a replication signal
- The two DNA loops attach to the membrane
- The membrane elongates and pinches off (cytokinesis), forming two cells
Properties of Prokaryotes
- DNA not enclosed within a membrane and forms on circular Chromosome - - - - DNA is free; not attached to proteins
- Lack membrane-bound organelles.
- Ribosomes are present in plasma membrane, but have no exterior membrane
- Cell wall is made up of a compound called peptidoglycan
- Usually divide by binary fission.
Small in size: 1-10 µm
Features of a Prokaryote
Below
Cytoplasm - P
internal fluid component of the cell
Nucleoid - P
region of the cytoplasm where the DNA is located (DNA strand is circular and called a genophore)
Plasmids - P
autonomous circular DNA molecules that may be transferred between bacteria (horizontal gene transfer)
Ribosomes - P
complexes of RNA and protein that are responsible for polypeptide synthesis (prokaryote ribosome = 70S)
Cell membrane - P
Semi-permeable and selective barrier surrounding the cell
Cell wall - P
rigid outer covering made of peptidoglycan; maintains shape and prevents bursting (lysis)
Slime capsule - P
a thick polysaccharide layer used for protection against dessication (drying out) and phagocytosis
Flagella - P
Long, slender projections containing a motor protein that enables movement (singular: flagellum)
Pili - P
Hair-like extensions that enable adherence to surfaces (attachment pili) or mediate bacterial conjugation (sex pili)
Eukaryote
Eukaryotes are organisms whose cells contain a nucleus.
Evolved from prokaryotic cells (via endosymbiosis)
compartmentalised by membrane-bound structures (organelles) that perform specific roles
Can be - Protista, Fungi, Plantae or Animalia
Organelles
Organelles are specialised sub-structures within a cell that serve a specific function.
Prokaryotic cells do not typically possess any membrane-bound organelles, whereas eukaryotic cells possess several
Ribosomes
Universal Organelle
Structure: Two subunits made of RNA and protein; larger in eukaryotes (80S) than prokaryotes (70S)
Function: Site of polypeptide synthesis (this process is called translation)
Cytoskeleton
Universal Organelle
Structure: A filamentous scaffolding within the cytoplasm (fluid portion of the cytoplasm is the cytosol)
Function: Provides internal structure and mediates intracellular transport (less developed in prokaryotes)
Plasma membrane
Structure: Phospholipid bilayer embedded with proteins (not an organelle per se, but a vital structure)
Function: Semi-permeable and selective barrier surrounding the cell
Nucleus
Eukaryotic Organelle
Structure: Double membrane structure with pores; contains an inner region called a nucleolus
Function: Stores genetic material (DNA) as chromatin; nucleolus is site of ribosome assembly
Endoplasmic Reticulum
Eukaryotic Organelle
Structure: A membrane network that may be bare (smooth ER) or studded with ribosomes (rough ER)
Function: Transports materials between organelles (smooth ER = lipids ; rough ER = proteins)
Golgi Apparatus
Eukaryotic Organelle
Structure: An assembly of vesicles and folded membranes located near the cell membrane
Function: Involved in the sorting, storing, modification and export of secretory products
Mitochondrion
Eukaryotic Organelle
Structure: Double membrane structure, inner membrane highly folded into internal cristae
Function: Site of aerobic respiration (ATP production)
Peroxisome
Eukaryotic Organelle
Structure: Membranous sac containing a variety of catabolic enzymes
Function: Catalyses breakdown of toxic substances (e.g. H2O2) and other metabolites
Centrosome
Eukaryotic Organelle
Structure: Double membrane structure with internal stacks of membranous discs (thylakoids)
Function: Site of photosynthesis – manufactured organic molecules are stored in various plastids
Chloroplast
Plant cells only
Structure: Double membrane structure with internal stacks of membranous discs (thylakoids)
Function: Site of photosynthesis – manufactured organic molecules are stored in various plastids
Vacuole (large and central)
Plant cells only
Structure: Fluid-filled internal cavity surrounded by a membrane (tonoplast)
Function: Maintains hydrostatic pressure (animal cells may have small, temporary vacuoles)
Cell Wall
Plant Cells Only
Structure: External outer covering made of cellulose (not an organelle per se, but a vital structure)
Function: Provides support and mechanical strength; prevents excess water uptake
Lysosome
Animal Cells Only
Structure: Membranous sacs filled with hydrolytic enzymes
Function: Breakdown / hydrolysis of macromolecules (presence in plant cells is subject to debate)
Electron microscopes
They use electron beams focused by electromagnets to magnify and resolve microscopic specimens
Transmission electron microscopes (TEM) generate high resolution cross-sections of objects
Scanning electron microscopes (SEM) display enhanced depth to map the surface of objects in 3D
Electron vs Light Microscopes
They have a much higher range of magnification (can detect smaller structures)
They have a much higher resolution (can provide clearer and more detailed images)
EM Cannot display living specimens in natural colours
Micrograph
A photo or digital image taken through a microscope to show a magnified image of a specimen
deduce cell function based on the relative abundance of various organelles:
Mitochondria – Cells with many mitochondria typically undertake energy-consuming processes (e.g. neurons, muscle cells)
ER – Cells with extensive ER networks undertake secretory activities (e.g. plasma cells, exocrine gland cells)
Lysosomes – Cells rich in lysosomes tend to undertake digestive processes (e.g. phagocytes)
Chloroplasts – Cells with chloroplasts undergo photosynthesis (e.g. plant leaf tissue but not root tissue)
Prokaryotes Summary
Pili – shown as single lines
Flagella – shown as thicker and significantly longer lines than the pili
Ribosomes – labelled as 70S
Cell wall – labelled as being composed of peptidoglycan; thicker than cell membrane
Shape – appropriate for bacteria chosen (e.g. E. coli is a rod-shaped bacillus)
Size – appropriate dimensions (e.g. length of cell twice the width)
Animal Cell Summary
Nucleus – shown as double membrane structure with pores
Mitochondria – double membrane with inner one folded into cristae ; no larger than half the nucleus in size
Golgi apparatus – shown as a series of enclosed sacs (cisternae) with vesicles leading to and from
Endoplasmic reticulum – interconnected membranes shown as bare (smooth ER) and studded (rough ER)
Ribosomes – labelled as 80S
Cytosol – internal fluid labelled as cytosol (‘cytoplasm’ is all internal contents minus the nucleus)
Plant Cell Summary
Vacuole – large and occupying majority of central space (surrounded by tonoplast)
Chloroplasts – double membrane with internal stacks of membrane discs (only present in photosynthetic tissue)
Cell wall – labelled as being composed of cellulose ; thicker than cell membrane
Shape – brick-like shape with rounded corners
Structure of Phospholipids
Consist of a polar head (hydrophilic) - glycerol and phosphate molecule
Consist of two non-polar tails (hydrophobic) - fatty acid (hydrocarbon) chains
Because phospholipids contain both hydrophilic (water-loving) and lipophilic (fat-loving) regions, they are classed as amphipathic
Arrangement in Membranes:
The hydrophobic tail regions face inwards and are shielded from the surrounding polar fluids, while the two hydrophilic head regions associate with the cytosolic and extracellular fluids respectively
