Cells

Cells

1. Prokaryotic

   • single cells e.g bacteria
   • DNA free in cytoplasm
   • circular DNA
   • cell wall
     • made of a polysaccharide
   • organelles not membrane bound
   • small ribosomes
   • very small cells
     • less than 2micrometres
   • flagellum
   • plasmid - ring of DNA

2. eukaryotic

   • complex cells
   • Animal
     • plasma membrane
       • made of lipids and protein
       • regulates substance movement in and out of cell
       • receptor molecules
     • nucleus
       • nucleolus
         • makes ribosomes
       • contains chromatin
         • made from proteins and DNA
     • golgi apparatus
       • flattened sacs
       • processes and packages new lipids and proteins
       • makes lyosomes
     • nuclear envelope
       • surrounds nucleus, has pores
         • allow substances to move between nucleus and cytoplasm
     • ribosome
       • in cytoplasm or on RER
       • site where proteins are made
     • rough endoplasmic rectilium
       • folds and processes proteins from ribosomes
     • smooth endoplasmic rectilium
       • synthesises and processes lipids
     • cytoplasm
     • mitochondrion
       • cristae on inside
       • site of aerobic respiration
         • ATP produced
     • lyosome
       • round, no internal structure
       • contains digestive enzymes
     • centriole
       • small, hollow cylinders
       • separates chromosones during cell division
     • cilia
       • hair-like structures
       • found on surface membrane
       • move substances along cell surface
     • flagellum
       • microubules contract to make flagellum moce
         • propel cells forward
   • Plant
     • same organelles as animal cells
     • chloroplast
       • internal structure
       • photosynthesis site
     • vacuole
     • cell wall
       • plasmodesmata
         • channels for exchanging substances between adjacent cells
       • celllose
       • supports plant cells
     • flagellum
   • Protein production
     • 1) proteins made at ribosomes
       • RER ribosomes make proteins to be excreted/attached to cell membrane
       • free ribosomes make proteins that stay in cytoplasm
     • 2) transported in vesicles to golgi apparatus
     • 3) golgi modifies and packs in vesicles to be transported around cell
   • Cytoskeleton
     • protein threads running through cytoplasm
       • microfilaments/microtubules
         • support cells organelles, keeping their position
     • help strengthen cell and maintain shape
     • transport organelles/materials within cell
     • proteins of cytoskeleton can cause cell to move

3. Microscopes

   • magnification
     • length of image/ length of specimen
     • how much bigger the image is than specimen
   • bigger unit to smaller unit = x 1000
   • smaller unit to bigger unit = / 1000
   • resolution
     • how well a microscope can distinguish between towo close together points
   • Light microscope
     • maximum resolution of 0.2 micrometres
     • maximum magnification x1500
     • light beams through object
     • objects can be stained to view object
       • different dyes are used to stain specific parts of cell
   • Electron
     • transmission elecrtron
       • electromagnets focus a beam of electrons through specimen
       • maximum resolution 0.0001 micrometres
       • show internal structures of organelles
       • maximum magnification more than x1000000
     • objects dipped in solution of metals, scatetering the electrons = staining specimen
       • black and white image
     • scanning electron
       • scan a beam of electrons across specimen
         • form 3D image
       • maximum resolution 0.005 micrometres
       • maximum magnification less than 1000000

4. Membranes

   • Structure
     • fluid mosiac model
       • model describing arrangement of molecules in the membrane
       • moving phospholipid molecules from a continious fluid bilayer
         • form a barrier to water soluble substances
           • centre is hydrophobic so water soluble substances cannot get through
           • small non polar substances can diffuse through
         • hydrophilic head and hydrophobic tail
           • from a bilayer, heads face toward water on either side of membrane
       • cholesterol
         • gives stability to membrane
         • fits between phospholipids
         • binds to hydrophobic tails of phospholipids
         • makes membrane less fluid, and more stable
         • has hydrophobic regions to create barrier to polar substances
       • glycolipids and glycoproteins
         • stabilise membrane
           • forms hydrogen bonds with surrounding water molecules
         • act as receptors for messenger molecules
     • plasma membranes control sibstances entering and leaving cell
     • partially permeable - let some molecules in but not others
   • Temperature
     • below 0 degrees
       • little energy for phosopholipids to move
       • channel proteins and carrier proteins denature
         • increasing permeability of membrane
       • ice crystals can pierce membrane = highly permeable
     • 0-45 degrees
       • phospholipids can move around
       • pertially permeable membrane
       • increase in temp = phospholipids move more = hgher permeability of membrane
     • 45+ degrees
       • bilayer starts to melt = more permeable membrane
       • water inside cell expands = pressure on membrane
       • channel and carrier proteins denature
         • no control over what enters/leaves cell
         • increased permeability

5. Cell signalling

   • 1) one cell releases a messenger molecule
     • messenger molecules can be hormones
     • messenger molecules can be drugs
       • trigger response or block the receptor
   • 2) molecule travels to another cell
   • 3) messenger molecule binds to receptors on target cell
   • 4) triggers cell response
   • membrane bound proteins act as receptors for specific messenger molecules
   • receptors are a specific shape to the messenger molecule
     • complmentary

6. Exchange

   • Diffusion
     • net movement of particles from an area of higher concentration to an area of lower concentration
     • gradient is the path from an area or high to low concentration
     • particles diffuse down a concentration gradient
     • continues until particles are evenly distributed
     • passive
     • Factors
       • concentration gradient
         • higher = faster rate
       • exchange surface thickness
         • thinner = faster rate
       • surface area
         • larger = faster rate
   • Osmosis
     • diffusion of water molecules across a partially permeable membrane
     • from an area of higher water potential to lower water potential
     • water potential
       • potential of water molecules to diffuse in or out of a solution
       • pure water = 0
       • any solution is negative
         • lower likelihood to diffuse
         • more negative = stronger concentration of solutes
       • Isotonic solutions
         • two solutions with the same water potential
         • no net movement of water in an isotonic solution
       • HypOtonic solutions
         • solution with higher water potential than inside of cell
         • weak concentration of solutes
         • plant cell - vacuole swells - turgid
         • animal cell - swell and bursts
       • HypERtonic solutions
         • solution with lower water potential than inside cell
         • plant cell - becomes flaccid - plasmolysis
         • animal cell - shrinks
         • strong concentration of solutes
   • Facilitated Diffusion
     • large molecules cannot diffuse directly through bilayer
     • moves particles down a concentration gradient
     • passive - no energy
     • carrier proteins
       • move large molecules into/out of cell
       • 1) large molecule attaches to carrier protein in membrane
       • 2) protein changes shape
       • 3) releases molecule on opposite side of membrane
       • different carrier proteins facilitate the diffusion of different molecules
     • channel proteins
       • form pores in membrane for smaller ions/polar molecules to diffuse through
       • different channel proteins facilitate the diffusion of different particles
   • Active Transport
     • uses energy from ATP to move molecules/ions across plasma membranes
     • against concentration gradient
     • uses carrier proteins in the same way as facilitated diffusion
   • Endocytosis
     • 1) cell surrounds molecule with part of plasma membrane
     • 2) membrane pinches off to form vesicle inside cell, with ingested molecule inside
     • some molecules too large to be taken by carrier proteins
   • Exocytosis
     • some substances need to be released from cell
     • 1) vesicles with substance pinch off from golgi sacs
     • 2) move toward plasma membrane
     • 3) vesicles fuse with plasma membrane, releasing contents outside of cell

7. Division

   • Cell cycle
     • process that all body cells use to grow and divide
     • 1) Mitosis
       • cell division
     • Interphase
       • 2) Gap phase 1
         • cell grows, new organelles/proteins made
       • 3) Synthesis
         • DNA replicated and checked for errors
       • 4) Gap phase 2
         • cell keeps growing, proteins for cell division made
       • DNA unravelled and replicated to double it's genetic content
       • organelles replicated and ATP content increased for cell division
     • Mitosis
       • chromosomes
         • 2 strands (chromatids) joined by a centromere
           • sister chromatids
           • 2 because the chromosome already made identical copy during interphase
       • 1) Prophase
         • chromosomes condense
         • centrioles move to opposite ends of cell
           • form spindle - protein fibres across cell
         • nuclear envelope breaks down
           • chromosomes free in cytoplasm
       • 2) Metaphase
         • chromosomes line up along middle of cell
           • spindle equator
         • chromosomes attach to spindle by centromere
       • 3) Anaphase
         • centromeres divide
           • separating each pair of sister chromatids
         • spindles contract
           • pulling chromatids to opposite ends of cell
       • 4) Telophase
         • chromatids reach opposite poles on spindle
         • nuclear envelope forms around each group of chromosomes
         • cytokineses occurs
           • division of cytoplasm
           • cell membrane constricts, pinching cell into two daughter cells
             • daughter cells are genetically identical to original cell and eachother
       • Plants
         • only cells in meristems can divide by mitosis
         • no centrioles - spindle forms without them
         • cytokinesis begins in centre of cell with a cell plate
   • Asexual
     • using mitosis
     • new organisms produced are genetically identical to parent cell
     • Budding
       • 1) parent cell swells on one side forming bud at surface
       • yeast cells
       • 2) interphase - relplication
       • 3) mitosis
         • replicated DNA, cytoplasm and organelles move into bud
       • 4) budding cell contains nucleus with identical copy of parent cell's DNA
       • 5) cytokinesis occurs
         • bud pinches off from parent cell forming new genetically identical cell
   • Sexual
     • homologus pairs
       • pairs of matching chromosomes
         • same size, same genes
       • body cells have diploid number of chromosomes (2n)
     • gametes
       • haploid number of chromosomes
         • one copy of each chromosome
       • haploid sperm fuses with haploid egg = diploid number of chromosomes
         • zygote formed
     • Meiosis
       • division in reproductive organs to produce gametes
       • cells formed are genetically different
       • 1) DNA replicates and coils up to form chromosomes
         • arrange into homologous pairs
       • 2) pairs swap parts of chromatids with eachother
         • chromatids now have new combination of alleles
       • 3) homologous pairs split in first division
         • any one chromosome can go into either of 2 new cells
       • 4) each chromosome splits in half in second division
         • any half can go into any 4 new cells
       • four new genetically different cells produced

8. Stem Cells

   • unspecialised cells
     • can develop into any type of cell
   • found in early embryos
   • Differentiation
     • stem cells divide to become new cells
     • process of how a cell becomes specialised for it's job
     • bone marrow
       • contain adult stem cells
       • stem cells divide and differentiate to replace worn out blood cells
         • erthrocyte and neutrophils
     • cambium
       • stem cells in plants
       • stem cells of cambium in root/shoot divide and differentiate to become xylem and phloem
       • cambium forms ring inside root/shoots
         • cells divide and grow out of ring
           • differentiating as they move away from cambium
   • Specialised cells
     • after differentiation, cells have specific function
       • structure adapted to perform function
     • erythrocytes
       • carry oxygen in blood
       • biconcave disc shape
         • large surface area for gas exchange
       • no nucleus
         • more room for haemoglobin
     • neutrophils
       • defend body against disease
       • flexible shape allows them to engulf foreign pathogens
       • many lysosomes to break down engulfed pathogens
     • epithelial cells
       • cover organ surfaces
       • cilia move particles away
       • microvilli folds in cell membrane to increase surface area
     • Sperm cells
       • have flagellum to swim to egg
       • many mitochondria for energy to swim
       • acrosome contains digestive enzymes
         • to penetrate surface of egg
     • Palisade mesophyll cells
       • many chloroplasts to absorb sunlight
       • photosynethesis
       • thin walls = CO2 can easily diffuse into cell
     • Root hair cells
       • absorb water and mineral ions from soil
       • large surface area for absorption
       • thin permeable cell wall for entry
       • many mitochondria for energy for active transport
     • Guard cells
       • pores in leaf for gas exchange
       • thin outer walls and thickened inner walls
         • bend outwards = opening stomata
           • allows gas exchange for photosynthesis
       • take up water and become turgid in light

9. Organisation

   • Tissues
     • group of cells specialised to work together to carry out a function
     • squamous epithelium
       • single layer of flat cells lining a surface
       • thin exchange for diffusion
       • alveoli in lungs
     • ciliated epithelium
       • layer of cells covered in cilia
       • on surfaces to move things
         • in trachea to move mucus
     • xylem
       • transports water around plant
       • supports plant
     • phloem
       • arranged in tubes, made up of sieve and companion cells
       • sieve cells have end walls (sieve plates) with holes in to move sap through
   • Cooperation
     • multicellular organisms work efficently as they have different cells specialised for different functions
     • cells, tissues + organs must cooperate to keep organism alive and running
     • Transport systems
       • carry substances between different cells
       • plants - xylem carry water + minerals from root hair cells to palisade
       • humans - circulatory system helps move substances around body in blood
     • Communication systems
       • allow communication between cells in different parts of organism
       • chemical systems using messenger molecules
       • nervous system
     • muscle cells depend on oxygen - which depend on erythrocytes to carry oxygen from lungs
   • Organs
     • group of tissues that work together to perform a function
     • lungs
       • carry out gas exchange
       • contain squamous epithelium in alveoli and ciliated epithelium in bronchi/trachea
       • elastic connective tissue and vascular tissue
   • Organ systems
     • organs working together to perform a function
     • respiratory
       • all organs involved in gas exchange
     • circulatory
       • all organs involved in blood supply