Topic 1 Bio

• spontaneous generation


  Until 19th century some biologists believed that life could appear in non-living material

  
  

  - this was called a spontaneuos generation

  
  

  - But there is no evidance that living things can be formed except by cell division
• Pasteur's experiment (Very important as it can be asked on P1,P2 and P3)


  1. Basically broths were stored in a swan-necked flasks that prevented airborne organisms from passing ( but it allowed air to pass)

  
  

  2. Then these broths were boiled to kill the pre-exsisitng micro-organisms (sterilsation)

  
  

  3. But growth didnt occur in the flask until the neck was broken off and the borth was exposed to the external contaminents

  
  

  4. So the conclusion was made that emergent bacterial growth was caused by external contaminents and NOT spontaneuos generation

  
  

  Cells can ONLY arise from pre-exsisitng cells + air doesnt contain a vital principle for life

  
• What is the endosymbiotic theory?

  Okay so it basically explains the origins of eukaryotic cells

  - and the symbiosis is when 2 organisms mutually help each other in order to survive

  
  

  - And what is endosymbiosis, well its when a smaller cell lives inside a vesicle in the cytoplasm of a larger cell ( and this happens because of endocytosis)

  
  

  - Then the smaller cell divides at least as frequently as the larger cell and over time the two cells become dependent on each other and it engulfs into mitochondrion or cytoplasm

  
• Endosymbiotic theory: Animal cells

  1. A cell that respires anaerobically takes in an aerobic bacterium though endocytosis

  
  

  2. The bacterium supplies ATP more efficiently (aerobic) to itself + the host

  
  

  3. and this gives the host an advantage and over time the aerobic bacterium evolves into a mitochondrion + the host into a heterotrophic eukaryote
• Endosymbiotic theory: Plant cells

  1. A heterotrophic cell takes in a photosynthetic bacterium through endocytosis

  
  

  2. The bacterium supplies it with organic compounds thus making it an autotroph

  
  

  3. And the bacterium evolves into a chloroplast over time and the host into a photosynthetic eukaryote
• Endosymbiosis diagram

  
• Chloroplast + Mitochondira = evidence

  DIVISION: Divide by binary fission, like prokaryotes

  MEMBRANES: Have a double membrane, as expected when cells are taken in by endocytosis

  DNA: Have their own naked, circular DNA just like prokaryotes

  RIBOSOMES: Synthesise some of their proteins by using 70s ribosomes just like prokaryotes
• What was the origin of the first cells?

  So we can theoretically trace the origins of cells to the first living cell

  - But before that living cells had to have evolved from non-living material

  
  

  But cells have been theorised to have occuredover 3 key stages:

  
  

  1. So first there was non-living synthesis of carbon compunds example: amino acids, sugars from simpler inorganic molecules

  
  

  2. There was an assembly of carrbon compounds into more complex polymers, and this couldve occured at deep sea vents that couldve supplied inorganic compounds and thermal energy for assembly

  
  

  3. formation of membranes could occur if phospholipids were some of the first polymers created, and the phospholipids would naturally assemble into a membrane allowing for different internal chemistry than that of the surroundings
• What was the Miller-Urey experiment?


  So they recreated the condiotions of pre-biotic earth by using a closed system of tubes

  § As water was boiled to vapour to represent the high temperature of the pre-biotic earth

  
  

  § then the vapour was mixed with gases such as NH3 CH4 and H2 that wouldve been abundant

  
  

  § And this mixture was exposed to electrical spark in order to stimulate the energy from lightning

  
• What was the first single-celled organism

  Evidence:- All species of organisms share the same geentic code- The genetic code has 64 codons and apart from minor varinations they have the same meaning —-> Basically how thye code for amino acids in alllllll organisms
• What is the cell theory?


  Well the cell theory explains that all living organisms are composed of cells

  
  

  then that the cell is the most basic unit strcuture and organization in organisms

  
  

  that cells arise from pre-exsisiting cells
• Now who formulated the first two parts of the cell theory?

  Schleiden and Schwaan
• Who coined the term "cell"?

  Robert hooke
• Exception to the cell theory:

  Striated Muscle cellThis cell has a single surrounding membrane but are multinucleated

  
  

  they are approx 1000X larger than normal human cells

  
  

  and it challenges the idea that cells function as a unit, and that cells have only one nucleus
• Exception to the cell theory:

  Giant AlgaeSo it can grow to the lenght of 100mm

  
  

  It is single-celled and although its very large it only has one nucleus

  
  

  - and it challenges the idea that organisms are always made of many cells
• Exception to the cell theory:

  Fungal HyphaeThe hyphae are aseptate, thus meaning that they arent compartmentalised

  
  

  and each hyphae is multinucleated since its an uninterbuted tube structure

  
  

  and it challenges the idea that living things are composed of discrete cellls
• What are the functions of life?

  MR. H GREN

  
  

  M —> Metabolism

  R —> Reproduction

  H —> Homeostasis

  G. -> Growth

  R —> Response

  E —> Excretion

  N. —-> Nutrition
• Functions of life in Paramecium

  
• Functions of life in chlamydomonas

  
• What substances does a cell need to exchange?

  Food, waste, heat, gases
• Roles of SA and V

  SA:

  The bigger the SA the more substances that can be absorbed and excreted through the plasma membrane

  
  

  Therefore big SA is beneficial

  
  

  V:

  The bigger the volume the greater the demand for necessaery metabolic reactiosn
• Now why does SA:V ratio limit the cell size?

  Because as the dimensions of a cell increase V increases proportionally faster than SA

  
  

  therefore SA:V ratio decreases with cell size

  
  

  lower relative SA reduces rate of exchange higher relative V increases metabolic demands
• How cells alter their SA:V ratio

  Sa -> animal cells increase SA to increase ratio

  V —> plant cells decrease V to increase ratio
• gene expression


  —- all cells contain all genes of an organism

  
  

  so humans have approx 25,000 genes

  -> in different cells different genes are expressed and turned on

  
  

  and genes encode for proteins which affects a cell thus resulting in differentiation and specialisation
• cell differentiation


  Basically the development of cells in different ways in order to carry out specific functions

  
  

  - and differentiation changes a cells size, shape and metabolic activity
• What are the emergent properties

  1. Shown by multicellular organisms

  2. Refers to the charateristics of the whole organism

  3. Emerges due to the interaction of the component parts of a complex structure
• What are stem cells?

  These are cells that arent fully differentiated and have the ability to become different types of cells
• Cell potency


  Totipotent: any type of cell

  Pluripotent: many but not all cells

  multipotent: limited number of cells

  unipotent: only once cell
• What are the stem cell properties?

  They are undifferentiated

  and they have the ability to renew themselves
• therapeutic usage of stem cells

  Stargardt’s diseaseJuvenile macular degeneration

  its a genetic disorder that develops in children and results in worsened vision. and embryonic stem cells that can develop into retina are injected into the back of the eyeball. And these cells attach to the retina and grow thus resulting in improved vision with limited side effects
• therapeutic usage of stem cells

  Leukemia- cancer of the bone marrow resutling in the overproduction of white blood cells

  and the stem cell treatment uses blood stem cells derived from donor from bone marrow tissues which will differentiate into new red and white blood cells
• Calculating Magnification


  size of image/actual size of specimen

  
• Phosphoplipids


  Amphipathic = has hydrophobic and hydrophilic components

  
• 3 plasma membrane models

  Gorter & Grendel —> approx 1924

  Danielli & Davson —> approx 1935

  Singer & Nicolson —> approc 1972
• Creation of Gorter and Grendel model

  - phospholipids were extracted from RBC and arranged in a monolayer

  - The area of the monolayer was double the area of the plasma memebrane of RBC

  - and this led them to deduce that phospholipids were formed a bilayer

  
• Evidence for D/D model

  
• Falsification of D/D model

  freeze-fracture technique:

  this technique involved the freezing of cells and then fracturing them along their lines of weakness

  
  

  - and this revealed proteins to be transmembrane, contradicting the D/D model that showed proteins on the external layers

  --> It also showed that the membrane was fluid and not rigid

  
  

  Fluorescent antibody tagging:

  antibodies that bind to membrane proteins were tagged with red and green fluorescent markers

  
  

  --> and this showed membrane proteins were free to move and not fixed in a static layer
• fluid mosaic model

  
• properties of the phospholipid bilayer (name at least 4)

  1. Held together by weak hydrophobic interactions between the tails

  
  

  2. individual phospholipids can move within the bilayer, allowing for membrane fluidity and flexibility

  
  

  3. Fluidity allows for spontaneous breaking and reforming of membrane

  
  

  4. Hydrophobic/hydrophilic layers restrict the passage of many substances
• functions of the membrane proteins


  Mnemonic: JET RAT

  Junctions --> serve to connect and join 2 cells together

  Enzymes --> Fixing to membranes localises metabolic pathways

  Transport --> channels for passive transport to allow hydrophilic particles across by facilitated diffusion --> Pumps for active transport which uses ATP to move particles across the membrane

  Recognition --> May function as markers for cellular identification

  Attachment --> attachment points for cytoskeleton + extracellular matrix

  Transduction --> receptors for hormones