Cells vary in size and shape. What limits how large and small cells can be?

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1 What limits how large and small cells can be? Cells vary in size and shape Minimum is determined by the total size of all the molecules required for cellular activity Maximum is limited by the need for sufficient surface area to carry out functions Essen%al idea: Eukaryotes have a much more complex cell structure than prokaryotes.

2 1.2.U3 Electron microscopes have a much higher resolution than light microscopes. Resolu'on is defined as the shortest distance between two points that can be dis3nguished Light microscopes are limited in resolu3on by the wavelengths of visible light ( nm). Electrons have a much shorter wavelength (2 12 pm) therefore electron microscopes have a much higher resolu3on Light microscopes are usually limited to 1000x because, due to the resolu3on, nothing is gained by increasing the magnifica3on try zooming in on an image on your laptop or phone ager a certain point there is no benefit to zooming in as the image becomes pixelated Millimetres (mm) resolution Micrometres (µm) Nanometres (nm) Human eye ,000 Light microscopes Electron microscopes hhp://upload.wikimedia.org/wikipedia/commons/c/c5/electron_microscope.jpg

3 Light microscopes allow us to see the structure of cells Electron microscopes allow us to see the ultrastructure of cells, such as these pancrea6c exocrine cells Electron microscopes can see viruses (0.1μm diameter), but light microscopes cannot

4 1.2 Ultra structure of a cell Prokaryotes versus Eukaryotes

5 1.2.4 Prokaryotes reproduce through Binary Fission Binary Fission asexual reproduction where cell divides into two smaller copies

6 Steps of Binary Fission 1. DNA is replicated semi-conservakvely 2. DNA loops (2) anach to the membrane 3. Membrane elongates and pinches off (cytokinesis) forming two separate cells 4. Two daughter cells are genekcally idenkcally (clones) Binary fission is also used by some organelles in eukaryotes

7 Prokaryotic cells - Relatively small/simple cells No organelles DNA is coiled into nucleoid region Cytoplasm has ribosomes

8 1.3.4 Compare Prokaryotic & Eukaryotic Cells Prokaryotic cells have naked DNA in the cytoplasm in a nucleoid region. Eukaryotes have chromosomes made up of DNA and protein in the nucleus inside a nuclear envelope. Prokaryotes have small ribosomes (70S) eukaryotes have large ribosomes (80S). Prokaryotes don t have mitochondria eukaryotes do. In prokaryotes there are no membrane bound organelles

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10 Differences between plant and animal cells Animal cells have a plasma membrane, plant cells have a plasma membrane and a cell wall. Animal cells do not have chloroplasts Animal cells store glycogen as their carbohydrate resource whereas plants store starch. Plants have a large vacuole that is always present. Animal cells can change shape due to the lack of a cell wall and are usually flexible

11 Advantages of Eukaryotic partitioned compartments Efficiency of metabolism - enzymes and substrates can localized and much more concentrated Localized condi9ons - ph and other such factors can be kept at opkmal levels. The opkmal ph level for one process in one part of the cell Toxic / damaging substances can be isolated, e.g. digeskve enzymes (that could digest the cell itself) are stored in lysosomes Numbers and loca9ons of organelles can be changed dependent on the cell s requirements.

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14 Explain how the hydrophobic and hydrophilic properties of phospholipids help maintain the structure of cell membranes. Phospholipids are amphipathic they are both polar and nonpolar. polar nonpolar

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16 Membrane proteins variety! structure position - peripheral v. integral functions (non-exhaustive list): hormone binding cell adhesion cell to cell communication channels for passive transport pumps for active transport

17 Glycolipids are used in cell recognition

18 Some glycoproteins are used as receptors for hormones

19 } Bind to special molecules and send messages to the cell. i.e. Need more water

20 } Anchored to cell membrane and connect cells. } Not bound to the membrane just hooked on. Connect cells.

21 } Move molecules in and out of cell. } i.e. = sugar molecules

22 } Move large or charged molecules in and out of cell. i.e. = Salt

23 hydrophobic and hydrophilic properties of phospholipids impact proteins. Integral proteins (transmembrane proteins) have to go through the membrane - need hydrophobic and hydrophilic parts

24 What about the cholesterol? found in animal membranes, between phospholipid tails. reduces fluidity and selective permeability more cellular control prevents crystallization of membrane

25 } Big term for things that connect cells to other cells. } Used to make tissues

26 Cell junctions Tight junctions bind cells into leakproof sheets Anchoring junctions link cells into strong tissues Communicating junctions:» Gap junctions allow substances to flow from cell to cell

27 Tight junctions Anchoring junction Gap junctions Extracellular matrix Space between cells Plasma membranes of adjacent cells