1. Cell Biology Flashcards
Cell Theory
- All living organisms are composed of cells
- The cell is the smallest unit of life
- Cells only arise from pre-existing cells
- The cell is the smallest unit of life
The functions of life (carried out by unicellular organisms)
Ex: Paramecium, chlorophyll
MRHGERN
- Metabolism: essential chemical reactions
- Reproduction: sexually or asexually
- Homeostasis: maintain a stable internal environment
- Growth: can move and change size/shape
- Excretion: exhibit the removal of waste
- Response: to internal and external stimuli
- Nutrition: either by synthesis or absorption of organic matter
Ex: Paramecium (cilia for movement)
Importance of large SA:V ratio
- As cell grows, volume increases faster than surface area, leading to a decreased SA:V ratio
- If metabolic rate > exchange rate of vital materials, cell eventually dies
- Thus cell divides to maintain smaller size again
Ex: villi and microvilli
Emergent properties (for multicellular organisms)
The whole is more than the sum of its parts- a complex system possesses properties that its constituent parts do not have
Thus multicellular organisms capable of performing functions unicellular organisms cannot
Cell differentiation
The process by which unspecialised cells changes and carries out a specific function in the body
- caused by activation of different genes
- expression of some genes and not others
Stem Cells
Able to continuously divide, replicate, and differentiate into any specialized cell
Difference between totipotent and pluripotent
Both can differentiate into any cell, but totipotent includes placental cells and pluripotent cannot differentiate into a whole organism i.e. blastocyst
Multipotent
Can differentiate into a few closely related types of body cell i.e. umbilical cord
Unipotent
Cannot differentiate, only capable of self-renewal
Stem Cell therapy
- trigger differentiation
- surgical implantation of cells
- suppression of host immune system
- monitor for cancerous growth
Stargardt’s Disease
Juvenile macular degeneration –> progressive loss of central vision
Replacing dead cells in the retina with functioning ones derived from stem cells
Leukemia
Cancer of the blood or bone marrow (abnormal white blood cells)
Hematopoietic stem cells (HSC) taken from bone marrow, patient undergoes chemotherapy
HSCs are transplanted back into bone marrow and differentiate into new healthy white blood cells
Ethical issues of stem cell therapy
For:
- Eliminates serious diseases in population
- Donating organs risks another human’s life
- Stem cells harvested from embryo at an early
stage
Against:
- Destruction of potential living organism
- May cause tumour
- Religious or moral objections
Embryos vs adult tissue stem cells
Check folder notes
Prokaryote structure
Cytoplasm Nucleoid- contains naked DNA Plasmids- transferable circular DNA 70S ribosomes Cell membrane Cell wall Pilli- helps in cell adhesion and transferring DNA Flagella- locomotion, propels cell Slime capsule- protection
Explain binary fission
Asexual reproduction
1. Circular DNA is replicated semi-conservatively 2. The two copies of the DNA loop move to opposite ends of the cell 3. Cell elongates and pinches off (cytokinesis), forming two identical daughter cells
Four kingdoms of Eukaryotes
- Protista
- Fungi
- Plantae
- Animalia
Compartmentalisation (eukaryotes only)
Greater efficiency of metabolisms
Optimal internal conditions
Isolation of toxic substance
Flexibility of changing number and position of organelles
Features of both plant and animal cells (9)
Plasma membrane- controls entry/exit Cytoplasm- internal structure & enzymes Mitochondria- cell respiration 80S ribosomes- protein synthesis Nucleus- genetic info Endoplasmic Reticulum- smooth and rough Golgi Apparatus- processes and packages Vesicle- transports Vacuole- osmotic balance
Plant cells only
Cell Wall- protection and shape
Chloroplasts- photosynthesis
Animal cells only
Lysosomes- hydrolytic enzymes, breaks down molecules
Centrioles- role in nuclear division
Electron Microscopy vs light microscopy
higher range of magnification and high resolution but not in colour
The Fluid Mosaic Model + who proposed it?
Biological membranes consist of phospholipid bilayers with proteins embedded in the bilayer
Singer and Nicholson
Why do phospholipids form bilayers in water?
Due to amphipathic properties of phospholipid molecules
- hydrophilic phosphate heads
- hydrophobic fatty acid tails
Cholesterol function
Improves stability and reduces fluidity
- membrane less permeable
- prevents crystallization
Difference in property of integral and peripheral proteins
Integral- amphipathic
Peripheral- polar
Membrane protein functions
CCRRE
Channels: passive transport
Carriers: use energy to change shape (protein pump)
Recognition: differentiates between self and non-self cells
Receptors: relay information (transmembrane)
Enzymes: enhance rate of reaction
The Davson-Danielli model
3 layers
lipo-protein sandwich- 2 layers of protein with central phospholipid bilayer
Assumptions of Davson-Danielli model
All membranes would be the same
Symmetrical surfaces
No Permeability
Falsification evidence (of Davson-Danielli model)
Proteins are amphipathic and varied in size
Fluorescent antibody tagging shows that membrane proteins move and are not static
Freeze fracturing reveals irregular rough surfaces inside membrane- transmembrane proteins present
Passive Transport
Along concentration gradient
Does not require ATP
Factors affecting rate of diffusion
- Temperature
- Surface area
- Size of particles
- Concentration gradient of diffusing particles
Facilitated diffusion (potassium channels in axon)
The K+ channels only allow the movement of K+ (inside to outside of axon for repolarisation)
Channels are voltage-gated to control neuron firing
Osmosis
The net movement of water molecules across a semi-permeable membrane from a region of low solute concentration to a region of high solute concentration
Hypertonic
High solute concentration- gains water
Plant cell in hypertonic solution –> plasmolyzed
Animal cell in hypertonic solution –> shriveled
Hypotonic
Low solute concentration- loses water
Plant cell in hypotonic solution–> turgid
Animal cell in hypotonic solution –> lysed
Application of osmolarity to medical procedures
Tissues and organs are bathed in a solution of same osmolarity as cytoplasm to prevent osmosis
Active Transport
Against concentration gradient
Uses ATP
Uses a carrier protein
Explain the sodium-potassium pump
- 3 sodium ions bind to intracellular sites on the sodium-potassium pump
- Phosphate group transferred to the pump via hydrolysis of ATP
- Pump undergoes conformational change, translocating sodium across membrane
- Conformational change exposes 2 potassium binding sites on extracellular surface of pump
- Phosphate group is released, pump returns to original conformation
- This translocate potassium ions across membrane
Vesicular transport
Proteins produced by ribosomes enter Rough ER
- Vesicles bud off from RER & carry proteins to Golgi apparatus - Vesicle fuses with Golgi apparatus, where proteins are modified and packaged - Vesicles bud off from Golgi apparatus & carry proteins to the membrane - Vesicles fuse with membrane and spill contents out of cell
Endocytosis
Phagocytosis: absorption of solids
Pinocytosis: ingestion of liquids
Exocytosis
Excretion: not useful materials
Secretion: vesicular transport
What allows for bulk transport (exo and endo cytosis)
The fluidity of the plasma membrane
Biogenesis (principle)
Principle that living organisms only arise from other living things by reproduction (not spontaneous generation)
‘Cells can only arise from pre-existing cells’
Louis Pasteur’s experiment
Broth in swan neck flasks boiled to sterilise
Growth only occurred if flask was broken or contents exposed to contaminants stuck in neck
Miller-Urey’s experiment’s recreated conditions of pre-biotic earth (to prove non-living synthesis)
High temperatures
A reducing atmosphere (no oxygen)
High radiation levels and electrical storms
Simple amino acids and hydrocarbons were synthesised
Conditions for emergence of life
- Simple organic molecules must be formed
- Larger organic molecules must be assembled from simpler organic molecules
- Organisms reproduce, replication of nuclei must be possible
- Biochemical reactions require optimal conditions (pH) –> membranes
The endosymbiosis theory
Mitochondria and chloroplasts were prokaryotes taken in by larger prokaryotes by endocytosis
- These cells remained undigested inside host cells and contribute new functionality to engulfing cell - Prokaryote and larger evolved to have a mutualistic relationship- prokaryote provide energy, larger cell provide nutrients
Evidence supporting the endosymbiosis theory
Double membranes- taken in by endocytosis
Singular naked DNA
70S ribosomes
Divide by binary fission
Mitosis
The division of the nucleus into two genetically identical daughter nuclei
Explain the 3 phases of interphase
G1: cell grows and preps for DNA replication, organelles duplicated
S: DNA is replicated
G2: cell finishes growing and preps for divison
Chromatin vs Chromosome
Chromatin: DNA loosely packed within nucleus, accessible for transcription/translation
Chromosome: DNA tightly wound around histones and condensed via supercoiling, inaccessible
When do DNA condense
in mitosis- only visible then
Explain prophase
DNA supercoils and chromosome condense --> sister chromatids Nucleolus disappears Nuclear membrane disintegrates Microtubule spindle fibres form Centrioles move to opposite poles
Explain metaphase
Spindle fibres bind to centromere of sister chromatids and cause their movement towards the equatorial plate
Sister chromatids align at equatorial plate (centre of cell)
Explain anaphase
Sister chromatids are separated (chromosomes) and pulled to opposite poles by spindle fibres
Explain telophase
Chromosomes have reached poles
Nuclear membrane starts to reform at each pole
Nucleolus appears in each new nucleus
Spindle fibres disintegrate
Cell elongates in prep for cytokinesis (which actually occurs concurrently, splitting cell in 2)
Mitotic index
Ratio of the number of cells in a population undergoing mitosis to the total number of visible cells
Cytokinesis in animal cell
- Microtubule filaments located immediately beneath plasma membrane at the equator pulls plasma membrane inwards
- Inward pull on plasma membrane forms a cleavage furrow
- When cleavage furrow reaches centre of cell, cell is completely pinched off, two daughter cells are produced
- Centripetal: moves from outside towards centre
Cytokinesis in plant cell
- Golgi apparatus forms vesicles carrying material to form new cell wall
- Vesicles merge and form the cell plate
- Cell plate grows and divides into two daughter cells
- Centrifugal: central and moves laterally
Cyclins
Cyclins bind to enzymes - cyclin-dependent kinases (CDKs) and activate them - forms a complex
Activated CDKs (the complex) attach phosphate groups to other (specific) proteins in the cell
Attachment of phosphate will trigger the target protein to carry out some specific event within the cell cycle (i.e. DNA replication)
Cyclin levels will peak when their target protein is required for function and remain at a lower levels other times
Benign tumour
localised, does not spread to other parts of the body
Malignant tumour
cancerous growth that is often resistant to treatment- may spread to other parts of the body, may recur after removal
How can a tumour occur
When events of a cell cycle are disrupted due to a mutation in a cyclin or CDK, or an associated protein
Cell may have lost ability to enter G1, mutation is passed on to daughter cells and a clump of cells form
Mutagens
Agents that cause gene mutations i.e. carcinogens, X-rays
Proto-oncogenes
gene codes for proteins that stimulate cell cycle etc. –> mutation causes it to become cancer-causing oncogene
Tumour suppressor genes
gene codes for proteins that repress cell cycle progression –> mutation stops its normal function of preventing tumour formation
Metastasis
Cancerous cells detach from the primary tumour
Some cancerous cells penetrates wall of lymph or blood vessels and so circulate the body
Circulating cancerous cells invade tissues at different locations and
develop, by uncontrolled cell division, into secondary tumours
Smoking and cancer
Correlation and not necessarily causation
