Cell evolution Flashcards
Cell theory
- All living organisms are composed of one or more cells
- The cell is the basic unit of structure and organization in organisms
- Cells arise from pre-existing cells
Relative sizes of different cells
Cell are measure in micro meters (um) - one one-thousandth of a mm
- 0.1 nm - Atoms
- 1nm - Lipids
- 5-10nm - Potein
- 100 nm - Flu virus (similar to Ribosome)
- 1um - Bacteria (Prokaryote cell), Mitochondria, Chloroplasts
- 10-100um - Plant & Animal cells
- 100um and a bit - Human egg
- 1mm - Frog egg
- 10mm and a bit - Chicken egg
- 100mm - ostridge egg
Advantages of cell being small
- ions & organic molecules in the environment efficiently enter the cell and rapidly diffuse throughout its volume
- This is important: cell is an open system (thermodynamics) and must transform energy from its environment into stored chemical energy that can be used for building and breaking down macromolecules (sucrose/glucose)
What happens if the cell grows too large
Surface area will be insufficient to support the rate of diffusion required for the increased volume
Prokaryotic cell size
- Relatively small
- Surface area-to-volume ration of 3:1
-> plenty of surface to absorb and can rapidly diffuse
Eukaryotic cell size
- Cells are 10-fold larger than Prokaryotic
- Surface area-to-volume ration of 0.3: 1
-> once something gets inside of the cell, it takes longer to diffuse throughout the entire volume
-> Solution: making compartments (used for specific purposes) within the cell help organize smaller spaces for chemical reactions to occur
Prokaryotic & Eukaryotic share 6 common components
- Macromolecules - Proteins, lipids, carbs
- Plasma membrane - Separates cell’s interior from its surrounding environment
- Cytoplasm - Consists of a jelly-like cytosol within the cell (watery)
- DNA and RNAs
- Ribosomes
- Enzymes
Prokaryotes: Bacteria
- Bacteria Cell wall: composed of proteins and sugars
- Bacteria Capsule: gives it shape and resilience, determines how things will enter the cell, protect the cell against toxins
- Bacteria Chromosome: molecule of double stranded DNA
- Ability of bacteria to resist freezing and remain in a fluid state bc it’s hard to freeze cytoplasm: quickly or slowly freeze it but it remains fluid. When temperature gets warmer, bacteria wake up
- Bacteria are so small that molecules can enter and diffuse across the cell in seconds
Eukaryotes: Animal cells
- Reduced S/V ratio selected for adaptations in animals cells. SO:
- Folding of membranes to increase surface area (minimize size/volume)
- Intracellular transport
- Organelles specialized for specific chemical reactions
- Everything in animal cells are dynamic at room temp.
Microfilaments and Microtubules (Animal Cells)
Rod-like structures composed of polymers similar to the polymers that make up the flagella in bacteria
- Related, have diff proteins
- Both: use energy stored in ATP or GTP to do chemical reactions
Eukaryotes: Plant cells
Plant cells are adapted for life in one place
- A rigid cell wall
- A central vacuole
-> Stores watery substances so plants can survive in drought (why you don’t need to water plants everyday)
The plasma membrane (all cells)
Barrier between the cell and the environment
- Barrier = permeable (allows things to come in)
-> Small uncharged molecules can diffuse across membrane - Integral membrane proteins: form a channel on their own or w another protein. They allow big molecules to be pumped into the cell across membrane barriers
- Cholesterol: makes membrane more fluid
- Glycoproteins (proteins mixed w sugars): form structures that are unique to you
Ribosomes (all cells)
- In cytoplasm
- Large and small subunits
- E, A, P sites
- Enzyme
- Essential for protein synthesis
Cytoplasm (and nucleoplasm)
- The aqueous environment of a cell
- Densely packed with molecules and macromolecules (Glycogen)
Organelles (Eukaryotes)
- Organelles: a collection of factories and assembly lines
-> Have their own membrane barriers
Organelle membranes
- Isolate chemical reactions
OR - Ensure that metabolic pathways involving many chemical reactions are efficient
Organelles: Nucleus
- Nucleus: a membrane compartment that holds the DNA
-> Huge surface area - Inside the nucleus: RNA polymerase is working on the DNA at the genes to produce mRNA
Organelles: Nuclear Pore
Allows mRNA has to leave the nucleus, and proteins need to move back and forth across through
Organelles: Nucleolus
- Specialized region of DNA
- Where the specialized mRNA required for ribosomes to function is synthesized.
Organelles: Nucleoplasm
- The aqueous environment within the nucleus
- Special chemical reactions needed for transcription occur in the nucleoplasm
NOTE: For translation, chemical reactions occur in the cytoplasm.
Organelles: Mitochondria
- Specialized for the synthesis of ATP
- Folded membranes with many different compartments
Micro-environments
- Membranes form Microenvironment that allow chemical reactions to occur without affecting the rest of the cell
-> Breaking down polysaccharides
-> Eliminating waste via Phagocytosis: lysosome containing digestive enzymes break down food vacuole
Intracellular transport system in Eukaryotes
Transport system: makes the diffusion of things linear through by restricting what things can diffuse in
- Nucleus, Rough Endoplasmic Reticulum and Golgi are connected
- These organelles are a combined protein synthesis and transport system
The Cytoskeleton (All cells)
Composed of specialized rods (Microfilaments and Microtubules) that grow and shrink
Cytoskeleton Functions
- Cell shape and cell movement
- Transport within cells
- Exerts force to move chromosome or cleave membranes
Microfilaments
- Actin = subunit of a microfilament/enzyme
- Actin are monomers, when bound to/collide w ATP or ADP (nucleotide) changes length of the microfilament
How do microfilaments increase in length
Concentration Actin-ATP high = increase in length
- Actin-ATP subunits can polymerize (join together) to form a microfilament. The energy stored in ATP helps drive this polymerization process,
How do microfilaments decrease in length (shrink to microfili)
Concentration Actin-ADP high = decrease in length
- As the microfilament grows, ATP is hydrolyzed (loses a phosphate group and releases energy) to form ADP.
- Actin-ADP subunits tend to depolymerize (break apart), causing the microfilament to shrink or decrease in length.
How do cells control their shape and size
By controlling how much ATP/ADP actin is coming in and out
- Growing actin helps cells change shape, move around, or perform specific tasks.
- Shrinkage assists in splitting or cutting the cell’s plasma membrane.
Microtubules
- Are composed of 13 rods/subunits that form a tube
- Concentration of tubulin-GTP and tubulin-GDP effects the length of the microtubule
How microtubules increase in length
Concentration tubulin-GTP high
How microtubules decrease in length
Concentration tubulin-GDP high
Example of Catastrophe
- When Tubulin starts to undergo hydrolysis, there is a mix of GDP and GTP-bound tubulin.
- When this happens: tubulin structures decompress, and the whole cellular structure collapses or falls apart.
Actin is necessary for cell divison
- Actin helps split the cell into two parts during cell division.
- Microtubules attach to chromosomes and pull them apart, allowing them to move to different parts of the cell.
- Cancer: when chromosomes don’t move properly during cell division causing uncontrolled cell division
Cells as bio machines
- Cells create large structures, like “bio-machines,” to do specific jobs.
Microscopy Example in Mammal Cells:
- To see things in a mammal cell under a microscope, we use the fact that chromosomes (structures in the cell) have different densities.
- Bc of diff densities, light bends differently when passing through chromosomes compared to other cell parts.
- This bending of light helps us see and study objects in the cell using a microscope.
Primary cilium
Sensory structure on every cell
Cilia
Cilia on cells that line lungs: Helps move things so that mucus does not pile up in lungs
Flagella
In bacteria, flagella are moving the cells around in single cell eukaryotic organisms
Cilia and Flagella are built from
Microtubules and motor proteins that use ATP to apply force
Plants have special organelles
- Central vacuole: stores watery sap
- Mitochondria
- Chloroplasts: where light radiant energy can be transformed into ATP
Evolution of the cell
- Inorganic molecules + water + heat = radiant energy
-> CO2 on early Earth absorbed energy from sunlight that was released as radiant energy
-> When this energy condenses and particles collide, it triggers chemical reactions that led to the formation of organic molecules - Organic molecules = building bocks of the macromolecules in living organisms
Evolution of the cell: DNA and RNA
- RNA before DNA
- RNA is how molecules remember info
- RNA can be translated into Proteins which can catalyze its own replication (DNA can’t do this)
Phospholipid membrane
- Acts as a barrier
- Forms watery environment that is suitable for chemical reactions such as:
-> RNA passed on through auto-catalyzed duplication
-> Cells increasing in number through fission
Evolution for Mitochondria and Chloroplasts
Endosymbiosis
- Host cells engulfed aerobic (needs oxygen) or photosynthetic (uses sunlight) bacteria
- Aerobic bacteria became mitochondria
- Autotrophic (Photosynthetic) bacteria became chloroplasts
NOTE:
- Mitochondria and Chloroplasts have their own DNA, Ribosomes, and RNAs
- Both similar size to bacteria
Models for evolution of Eukaryotes
- Nucleus first
- Mitochondria first
- Eukaryote first
- The idea that bacteria, animals, and plants share a common ancestor.
- Archaea (type of microorganism) have the ability to perform photosynthesis.
-> Suggests that the common ancestor of bacteria, animals, and plants might have also had the potential for photosynthesis.
Web of life hypothesis
- Ancestral community of primitive cells gave rise to bacteria, archaea, and eukarya
Electron microscopes
- Nanometer resolution 1x10-9 m - individual molecules are visible
-> Ex. To understand microtubule structure:
-> Slice through frozen cell that had been treated with a dye that binds to proteins in a particular way and is very dense
-> so when the electrons hit it, they are either absorbed or scatter
Super-resolution light microscope
- Chromosome Segregation during mitosis
- Chromosomes are denser than the Cytoplasm and Membranes
- Can be detected by their refraction (contrast) of white light
Light microscopes: How can we detect cellular components in living cells?
Bioluminescent organisms such as jellyfish gave us a tool that changed the life sciences: GFP protein
Fluorescent Microscopy
- Because of the degeneracy of the genetic code, the GFP protein can be produced by many types of cells
- Blue light excites protein and will produce green light which represents GFP protein
Protein engineering
By introducing a series of amino acid mutations into jellyfish GFP, scientists created a colour palette for cells
- Blue to Yellow = GFP (Eukaryotic)
- Yellow to Red = RFP (Prokaryotic)
Super-resolution fluorescence microscopy
- 60 nanometer resolution
- Can see dynamic growth and shrinkage of microtubules by tracking the movement of the green
