Cells

Cells

Prokaryotic
1. single cells e.g bacteria
2. DNA free in cytoplasm
3. circular DNA
4. cell wall
  1. made of a polysaccharide
5. organelles not membrane bound
6. small ribosomes
7. very small cells
  1. less than 2micrometres
8. flagellum
9. plasmid - ring of DNA
eukaryotic
1. complex cells
2. Animal
  1. plasma membrane
    1. made of lipids and protein
    2. regulates substance movement in and out of cell
    3. receptor molecules
  2. nucleus
    1. nucleolus
      1. makes ribosomes
    2. contains chromatin
      1. made from proteins and DNA
  3. golgi apparatus
    1. flattened sacs
    2. processes and packages new lipids and proteins
    3. makes lyosomes
  4. nuclear envelope
    1. surrounds nucleus, has pores
      1. allow substances to move between nucleus and cytoplasm
  5. ribosome
    1. in cytoplasm or on RER
    2. site where proteins are made
  6. rough endoplasmic rectilium
    1. folds and processes proteins from ribosomes
  7. smooth endoplasmic rectilium
    1. synthesises and processes lipids
  8. cytoplasm
  9. mitochondrion
    1. cristae on inside
    2. site of aerobic respiration
      1. ATP produced
  10. lyosome
    1. round, no internal structure
    2. contains digestive enzymes
  11. centriole
    1. small, hollow cylinders
    2. separates chromosones during cell division
  12. cilia
    1. hair-like structures
    2. found on surface membrane
    3. move substances along cell surface
  13. flagellum
    1. microubules contract to make flagellum moce
      1. propel cells forward
3. Plant
  1. same organelles as animal cells
  2. chloroplast
    1. internal structure
    2. photosynthesis site
  3. vacuole
  4. cell wall
    1. plasmodesmata
      1. channels for exchanging substances between adjacent cells
    2. celllose
    3. supports plant cells
  5. flagellum
4. Protein production
  1. 1) proteins made at ribosomes
    1. RER ribosomes make proteins to be excreted/attached to cell membrane
    2. free ribosomes make proteins that stay in cytoplasm
  2. 2) transported in vesicles to golgi apparatus
  3. 3) golgi modifies and packs in vesicles to be transported around cell
5. Cytoskeleton
  1. protein threads running through cytoplasm
    1. microfilaments/microtubules
      1. support cells organelles, keeping their position
  2. help strengthen cell and maintain shape
  3. transport organelles/materials within cell
  4. proteins of cytoskeleton can cause cell to move
Microscopes
1. magnification
  1. length of image/ length of specimen
  2. how much bigger the image is than specimen
2. bigger unit to smaller unit = x 1000
3. smaller unit to bigger unit = / 1000
4. resolution
  1. how well a microscope can distinguish between towo close together points
5. Light microscope
  1. maximum resolution of 0.2 micrometres
  2. maximum magnification x1500
  3. light beams through object
  4. objects can be stained to view object
    1. different dyes are used to stain specific parts of cell
6. Electron
  1. transmission elecrtron
    1. electromagnets focus a beam of electrons through specimen
    2. maximum resolution 0.0001 micrometres
    3. show internal structures of organelles
    4. maximum magnification more than x1000000
  2. objects dipped in solution of metals, scatetering the electrons = staining specimen
    1. black and white image
  3. scanning electron
    1. scan a beam of electrons across specimen
      1. form 3D image
    2. maximum resolution 0.005 micrometres
    3. maximum magnification less than 1000000
Membranes
1. Structure
  1. fluid mosiac model
    1. model describing arrangement of molecules in the membrane
    2. moving phospholipid molecules from a continious fluid bilayer
      1. form a barrier to water soluble substances
        centre is hydrophobic so water soluble substances cannot get through
        small non polar substances can diffuse through
      2. hydrophilic head and hydrophobic tail
        from a bilayer, heads face toward water on either side of membrane
    3. cholesterol
      1. gives stability to membrane
      2. fits between phospholipids
      3. binds to hydrophobic tails of phospholipids
      4. makes membrane less fluid, and more stable
      5. has hydrophobic regions to create barrier to polar substances
    4. glycolipids and glycoproteins
      1. stabilise membrane
        forms hydrogen bonds with surrounding water molecules
      2. act as receptors for messenger molecules
  2. plasma membranes control sibstances entering and leaving cell
  3. partially permeable - let some molecules in but not others
2. Temperature
  1. below 0 degrees
    1. little energy for phosopholipids to move
    2. channel proteins and carrier proteins denature
      1. increasing permeability of membrane
    3. ice crystals can pierce membrane = highly permeable
  2. 0-45 degrees
    1. phospholipids can move around
    2. pertially permeable membrane
    3. increase in temp = phospholipids move more = hgher permeability of membrane
  3. 45+ degrees
    1. bilayer starts to melt = more permeable membrane
    2. water inside cell expands = pressure on membrane
    3. channel and carrier proteins denature
      1. no control over what enters/leaves cell
      2. increased permeability
Cell signalling
1. 1) one cell releases a messenger molecule
  1. messenger molecules can be hormones
  2. messenger molecules can be drugs
    1. trigger response or block the receptor
2. 2) molecule travels to another cell
3. 3) messenger molecule binds to receptors on target cell
4. 4) triggers cell response
5. membrane bound proteins act as receptors for specific messenger molecules
6. receptors are a specific shape to the messenger molecule
  1. complmentary
Exchange
1. Diffusion
  1. net movement of particles from an area of higher concentration to an area of lower concentration
  2. gradient is the path from an area or high to low concentration
  3. particles diffuse down a concentration gradient
  4. continues until particles are evenly distributed
  5. passive
  6. Factors
    1. concentration gradient
      1. higher = faster rate
    2. exchange surface thickness
      1. thinner = faster rate
    3. surface area
      1. larger = faster rate
2. Osmosis
  1. diffusion of water molecules across a partially permeable membrane
  2. from an area of higher water potential to lower water potential
  3. water potential
    1. potential of water molecules to diffuse in or out of a solution
    2. pure water = 0
    3. any solution is negative
      1. lower likelihood to diffuse
      2. more negative = stronger concentration of solutes
    4. Isotonic solutions
      1. two solutions with the same water potential
      2. no net movement of water in an isotonic solution
    5. HypOtonic solutions
      1. solution with higher water potential than inside of cell
      2. weak concentration of solutes
      3. plant cell - vacuole swells - turgid
      4. animal cell - swell and bursts
    6. HypERtonic solutions
      1. solution with lower water potential than inside cell
      2. plant cell - becomes flaccid - plasmolysis
      3. animal cell - shrinks
      4. strong concentration of solutes
3. Facilitated Diffusion
  1. large molecules cannot diffuse directly through bilayer
  2. moves particles down a concentration gradient
  3. passive - no energy
  4. carrier proteins
    1. move large molecules into/out of cell
    2. 1) large molecule attaches to carrier protein in membrane
    3. 2) protein changes shape
    4. 3) releases molecule on opposite side of membrane
    5. different carrier proteins facilitate the diffusion of different molecules
  5. channel proteins
    1. form pores in membrane for smaller ions/polar molecules to diffuse through
    2. different channel proteins facilitate the diffusion of different particles
4. Active Transport
  1. uses energy from ATP to move molecules/ions across plasma membranes
  2. against concentration gradient
  3. uses carrier proteins in the same way as facilitated diffusion
5. Endocytosis
  1. 1) cell surrounds molecule with part of plasma membrane
  2. 2) membrane pinches off to form vesicle inside cell, with ingested molecule inside
  3. some molecules too large to be taken by carrier proteins
6. Exocytosis
  1. some substances need to be released from cell
  2. 1) vesicles with substance pinch off from golgi sacs
  3. 2) move toward plasma membrane
  4. 3) vesicles fuse with plasma membrane, releasing contents outside of cell
Division
1. Cell cycle
  1. process that all body cells use to grow and divide
  2. 1) Mitosis
    1. cell division
  3. Interphase
    1. 2) Gap phase 1
      1. cell grows, new organelles/proteins made
    2. 3) Synthesis
      1. DNA replicated and checked for errors
    3. 4) Gap phase 2
      1. cell keeps growing, proteins for cell division made
    4. DNA unravelled and replicated to double it's genetic content
    5. organelles replicated and ATP content increased for cell division
  4. Mitosis
    1. chromosomes
      1. 2 strands (chromatids) joined by a centromere
        sister chromatids
        2 because the chromosome already made identical copy during interphase
    2. 1) Prophase
      1. chromosomes condense
      2. centrioles move to opposite ends of cell
        form spindle - protein fibres across cell
      3. nuclear envelope breaks down
        chromosomes free in cytoplasm
    3. 2) Metaphase
      1. chromosomes line up along middle of cell
        spindle equator
      2. chromosomes attach to spindle by centromere
    4. 3) Anaphase
      1. centromeres divide
        separating each pair of sister chromatids
      2. spindles contract
        pulling chromatids to opposite ends of cell
    5. 4) Telophase
      1. chromatids reach opposite poles on spindle
      2. nuclear envelope forms around each group of chromosomes
      3. cytokineses occurs
        division of cytoplasm
        cell membrane constricts, pinching cell into two daughter cells
        daughter cells are genetically identical to original cell and eachother
    6. Plants
      1. only cells in meristems can divide by mitosis
      2. no centrioles - spindle forms without them
      3. cytokinesis begins in centre of cell with a cell plate
2. Asexual
  1. using mitosis
  2. new organisms produced are genetically identical to parent cell
  3. Budding
    1. 1) parent cell swells on one side forming bud at surface
    2. yeast cells
    3. 2) interphase - relplication
    4. 3) mitosis
      1. replicated DNA, cytoplasm and organelles move into bud
    5. 4) budding cell contains nucleus with identical copy of parent cell's DNA
    6. 5) cytokinesis occurs
      1. bud pinches off from parent cell forming new genetically identical cell
3. Sexual
  1. homologus pairs
    1. pairs of matching chromosomes
      1. same size, same genes
    2. body cells have diploid number of chromosomes (2n)
  2. gametes
    1. haploid number of chromosomes
      1. one copy of each chromosome
    2. haploid sperm fuses with haploid egg = diploid number of chromosomes
      1. zygote formed
  3. Meiosis
    1. division in reproductive organs to produce gametes
    2. cells formed are genetically different
    3. 1) DNA replicates and coils up to form chromosomes
      1. arrange into homologous pairs
    4. 2) pairs swap parts of chromatids with eachother
      1. chromatids now have new combination of alleles
    5. 3) homologous pairs split in first division
      1. any one chromosome can go into either of 2 new cells
    6. 4) each chromosome splits in half in second division
      1. any half can go into any 4 new cells
    7. four new genetically different cells produced
Stem Cells
1. unspecialised cells
  1. can develop into any type of cell
2. found in early embryos
3. Differentiation
  1. stem cells divide to become new cells
  2. process of how a cell becomes specialised for it's job
  3. bone marrow
    1. contain adult stem cells
    2. stem cells divide and differentiate to replace worn out blood cells
      1. erthrocyte and neutrophils
  4. cambium
    1. stem cells in plants
    2. stem cells of cambium in root/shoot divide and differentiate to become xylem and phloem
    3. cambium forms ring inside root/shoots
      1. cells divide and grow out of ring
        differentiating as they move away from cambium
4. Specialised cells
  1. after differentiation, cells have specific function
    1. structure adapted to perform function
  2. erythrocytes
    1. carry oxygen in blood
    2. biconcave disc shape
      1. large surface area for gas exchange
    3. no nucleus
      1. more room for haemoglobin
  3. neutrophils
    1. defend body against disease
    2. flexible shape allows them to engulf foreign pathogens
    3. many lysosomes to break down engulfed pathogens
  4. epithelial cells
    1. cover organ surfaces
    2. cilia move particles away
    3. microvilli folds in cell membrane to increase surface area
  5. Sperm cells
    1. have flagellum to swim to egg
    2. many mitochondria for energy to swim
    3. acrosome contains digestive enzymes
      1. to penetrate surface of egg
  6. Palisade mesophyll cells
    1. many chloroplasts to absorb sunlight
    2. photosynethesis
    3. thin walls = CO2 can easily diffuse into cell
  7. Root hair cells
    1. absorb water and mineral ions from soil
    2. large surface area for absorption
    3. thin permeable cell wall for entry
    4. many mitochondria for energy for active transport
  8. Guard cells
    1. pores in leaf for gas exchange
    2. thin outer walls and thickened inner walls
      1. bend outwards = opening stomata
        allows gas exchange for photosynthesis
    3. take up water and become turgid in light
Organisation
1. Tissues
  1. group of cells specialised to work together to carry out a function
  2. squamous epithelium
    1. single layer of flat cells lining a surface
    2. thin exchange for diffusion
    3. alveoli in lungs
  3. ciliated epithelium
    1. layer of cells covered in cilia
    2. on surfaces to move things
      1. in trachea to move mucus
  4. xylem
    1. transports water around plant
    2. supports plant
  5. phloem
    1. arranged in tubes, made up of sieve and companion cells
    2. sieve cells have end walls (sieve plates) with holes in to move sap through
2. Cooperation
  1. multicellular organisms work efficently as they have different cells specialised for different functions
  2. cells, tissues + organs must cooperate to keep organism alive and running
  3. Transport systems
    1. carry substances between different cells
    2. plants - xylem carry water + minerals from root hair cells to palisade
    3. humans - circulatory system helps move substances around body in blood
  4. Communication systems
    1. allow communication between cells in different parts of organism
    2. chemical systems using messenger molecules
    3. nervous system
  5. muscle cells depend on oxygen - which depend on erythrocytes to carry oxygen from lungs
3. Organs
  1. group of tissues that work together to perform a function
  2. lungs
    1. carry out gas exchange
    2. contain squamous epithelium in alveoli and ciliated epithelium in bronchi/trachea
    3. elastic connective tissue and vascular tissue
4. Organ systems
  1. organs working together to perform a function
  2. respiratory
    1. all organs involved in gas exchange
  3. circulatory
    1. all organs involved in blood supply

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	Created by Gemma Bradford over 11 years ago