AS LEVEL BIOLOGY CHAPTER 1
Lysosomes (0.1-0.5μm):
(0.1-0.5μm): a single membrane with no internal structure in animal cells. They contain digestive (hydrolytic) enzymes that's kept separate from rest of cell to prevent damage. o Responsible for breakdown of unwanted structures eg old organelles or whole cells, in WBC to digest bacteria.
Steps for respiration
1. Energy is released from energy-rich molecules such as sugars and fats 2. This energy is transferred to molecules of ATP 3. The reactions of respiration then that place in the matrix and the cristae. The matrix contains enzymes in the solution (Krebs cycle) and these supply the hydrogen and electrons to the reactions in the cristae. 4. The flow of electrons along a precisely placed electron carriers in the membrane of the cristae is what provides the power to generate ATP molecules. (The foldings of the cristae increase the efficiency of respiration because it increases the surface area available for these reactions to take place.) 5. Once made, ATP leaves the mitochondrionand it spreads rapidly to all parts of the cell where energy is needed. 6. Energy is released by breaking ATP to ADP, a reversible hydrolysis reaction.
Step of photosynthesis
1. Light dependent stage- Light energy is absorbed by photosynthetic pigments (chlorophyll). Some energy is used to manufacture ATP from ADP(essential stage is splitting water into hydrogen and oxygen.) Hydrogen is used as a fuel which is oxidised to provide the energy to make ATP. This requires electron transport hence chloroplasts contain a complex system of membranes which contain photosynthetic pigments and electron carriers needed for the light dependent stage. (The chloroplasts can change orentation within the cell in order to receive maximum light.) 2. Light independent stage- Uses energy to convert carbon dioxide into sugars. This requires a cycle of enzyme controlled reactions called the Calvin cycle and takes place in the solution in the stroma. The sugars made are stored in forms of starch grains in stroma (way to identify a chloroplast).
Rough endoplasmic reticulum:
80S ribosomes of the rough endoplasmic reticulum are sites for protein synthesis and produce the rough appearance. The R.E.R provides a pathway for transport of materials through cell. o Made of two-dimensional flattened sacs, which are membrane-enclosed structures. o Proteins made by ribosomes on RER enter sacs and move through them. Transport vesicles bud off from the RER and join forming the Golgi body.
Structures of animal cells which can be seen in a high quality light microscope
Cell membrane Cytoplasm Golgi body Centrioles Mitochondria small structures Nuclear membrane Nucleoplasm Nucleus Nucleolus Chromatin Nuclear envelope
Ultrastructure of an animal cell as seen through an electron microscope
Cell membrane Cytoplasm Golgi body and vesicles Centrioles (two at right angles to each other) Mitochondria (and cristae) Lysosomes ER (rough and smooth) Ribosomes Microvilli Microtubules Nuclear membrane Nucleoplasm Nuclear pores Nucleus Nucleolus Chromatin Nuclear envelope
Structures of animal cells which can be seen in a low quality light microscope
Cell membrane Cytoplasm Nuclear membrane Nucleoplasm Nucleus Nucleolus
Structures of plant cells which can be seen in a low quality light microscope
Cell wall Nucleus Nucleolus Chloroplasts
Ultrastructure of a plant cell as seen through an electron microscope
Cell walls Cell membrane Cytoplasm Middle lamella Chloroplasts (and envelope) Grana ER (rough and smooth) Golgi body and vesicles Mitochondria (and cristae) Lysosomes Ribosomes Vacuole ( and tonoplast and cell sap) Microtubules Nuclear membrane Nucleoplasm Nuclear pores Nucleus Nucleolus Chromatin Nuclear envelope
Structures of plant cells which can be seen in a high quality light microscope
Cell walls Cell membrane Middle lamella (thin layer holding cells together) plasmodesmata Nucleus Nucleolus Chloroplasts (grana just visible) small structures Golgi body Vacuole Mitochondria
Microvilli
Fingerlike extensions of plasma membrane of apical epithelial cells, increase surface area, aid in absorbtion, exist on every moist epithelia, but most dense in small intestine and kidney
Single membraned organelles
Lysosomes Peroxisomes Vacuoles Golgi body
Microfilaments (7nm)
Made up of twisted double chains (cylinder) of G actin and F actin subunits. Its main function is to create tension and provide support. It also helps cells move.
Double membraned organelles
Mitochondria Chloroplasts Nucleus ER Nucleus
endosymbiont theory
Mitochondrion and chloroplast were bacteria that now live inside larger cells of animals and plants, which is why chloroplast and mitochondrion have circular DNA. Evidence: 1. Bacteria, mitochondria, and chloroplasts have 70s ribosome while eukaryotes have 80s ribosomes. 2. They have circular DNA 3. They are of similar size 4. They are all double membraned
Size of organelles (largest to smallest)
Nucleus (1500 nm) --> Chloroplast --> centrioles --> Mitochondria --> Lysosomes --> Nucleoli --> ribosome
membrane less organelles
Ribosomes Centrioles Nucleus
Ribosomes:
Ribosomes: the site at which mRNA (transcribed from the nucleus) is translated into polypeptides with the help of tRNA, therefore help with protein synthesis.
Electron microscopy
Source of radiation- electrons Wavelength- +- 0.005 nm Maximum resolution - .1 to .5 nm magnification- 5000000X Radiation source - high voltage tungsten lamp lens- magnets Specimen- Dry and dead Screen -fluorescent screen Stains- heavy metals Vacuum
Light microscopy
Source of radiation-Visible light (colors) Wavelength -400 to 700 nm Maximum resolution - 200 nm magnification- 1000X - 1500X Radiation source - tungsten or quartz halogen lamp lens- glass Specimen- Alive Screen -human eye/eye piece Stains- colored dyes Air filled
Cell surface membrane (7nm):
a selectively permeable membrane in plant and animal cells that allows for the exchange of certain biological molecules and ions. o Extremely thin with trilaminar appearance o It is comprised of phospholipid bilayers which are assembled with the hydrophilic phosphate heads facing the aqueous environment (inside and outside the cell) and the hydrophobic tails facing each other. Function: CHAPTER 4 ▪ Barrier between cytoplasm and external environment ▪ Cell signalling ▪ Cell recognition (surface antigens) ▪ Cell-to-cell adhesion ▪ Site for enzyme catalysed reactions ▪ Anchoring the cytoskeleton ▪ Selection of substances that enter/leave the cell ▪ Formation of Hydrogen bonds with water for stability
Resolution
ability to distinguish between two separate points. The amount of detail that can be seen- higher resolution, higher detail. Limit of resolution: half the wavelength of radiation used to view specimen.
why do electron microscopes have a higher resolution?
electron beams have a shorter wavelength
Chloroplasts (3-10μm):
elongated shape, this cell structure is only found in plant cells in the palisade mesophyll, spongy mesophyll and surface of stem and carries out photosynthesis. o It has a double membrane (chloroplast envelope) and contains flattened fluid filled sacs known as thylakoids. o Chlorophyll is embedded in thylakoid membranes. o Thylakoids stacked on top of each other to form flat disk like grana. o Grana are linked by lamella. These structures are present in a matrix called the stroma. o Contains starch grains, circular DNA and 70S ribosomes.
Centriole (200nm diameter, 500 nm long):
formed by 9 triplets of microtubules. From each triplet microtubule, one is complete and other 2 are partial. Microtubules extend from centriole and attach themselves to kinetochore of chromosomes, forming spindle fibres. Centrioles duplicate, and a pair of centrioles then move to opposite poles of the cell (2 centrosome regions), thus separating sister chromatids during nuclear division. o Centrioles at bases of cilia and flagella (basal bodies) act as MTOCs. Microtubules extending from basal bodies into cilia and flagella help with their beating movements.
Organelles:
functionally and structurally distinct part of a cell, usually membrane bound. A generalised animal cell (20μm): A generalised plant cell (40 μm):
advantages and disadvantages of SEM?
good- 3d image (depth of field) bad- only dead specimens, black and white image, artefacts
advantages and disadvantages of TEM?
good- highest magnification and resolution bad- artefacts made, only dead specimens, need to be thin, black and white, 2d image
Magnification
if the number if times greater that an image is than the actual object (how much bigger it is) Depends on the power of the objective and eyepiece lens used. magnification = image/actual
why do electron microscopes need to be in a vacuum?
in air, oxygen molecules could collide with electrons and prevent electrons from reaching specimen
Types of microscopy
light microscopy and electron microscopy
Microtubules:
long hollow tubes that make up the cytoskeleton which helps determine cell shape. o Made up of alpha and beta tubulin that combine to form dimers. o Dimers join end to end to form protofilaments (polymerisation). o 13 protofilaments line up alongside each other in a ring to form a cylinder with a hollow center ie microtubule. o Forms an intracellular transport system by moving along secretary vesicles, organelles and cell components on its outer surface.
Virus:
non- cellular (non living) and are parasitic as they reproduce by infecting and taking over living cells. The virus DNA/ RNA hijacks the protein synthesising machinery of the host cell, which then helps to make new viral proteins to make capsid. STRUCTURE: Contain a protein coat (capsid) made of separate protein molecules called capsomeres. Glycoproteins and lipids stick out from the structure. Also CONTAIN REVERSE TRANSCRIPTASE. Reverse transcription is the conversion of mRNA to DNA.
Prokaryote:
organisms that lack a nucleus and have simpler structure eg bacteria.
Eukaryote:
organisms with a true nucleus and have membrane bound organelles eg animals, plants, fungi, protoctist.
Centrosome:
pair of centrioles at right angles that's involved in nuclear division and act as MTOCs.
Plasmodesmata:
pore-like structures found in cell walls that allow a link between neighbouring cells by fine threads of cytoplasm.
Cell wall (10 nm):
rigid as it contains fibres of cellulose (polysaccharide). o Gives the cell its definite shape and prevents it from bursting (by osmosis), allowing turgidity. o May be reinforced by lignin for extra strength. o Freely permeable.
Mitochondria (1μm):
sausage shaped, cylinderical structure surrounded by mitochondrial envelope and is more in areas that require maximal energy. o Has a matrix that contains 70S ribosomes and circular DNA which is used to make some of the mitochondrion's own proteins. o Cristae: finger like folding of inner membrane that projects into interior solution, matrix. o Intermembrane space: space between the two membranes. o Porin: transport protein in outer membrane, forms wide aqueous channel allowing water-soluble molecules from cytoplasm to intermembrane space. o Inner membrane: selective barrier controlling entrance of ions and molecules into the matrix. THE NUMBER OF MITOCHONDRIA CAN VARY DEPENDING ON THE NEED OF THE CELL. Function: Provides energy for aerobic respiration and may also synthesizes lipids.
Smooth Endoplasmic reticulum:
site for lipid synthesis and steroids eg cholesterol and reproductive hormones. o Meshwork of tubular membrane vesicles with fluid filled sacs that have no ribosome on its surface
Golgi body/complex/apparatus:
stack of flattened sacs formed by transport vesicles which bud off of the RER, and broken down to form Golgi vesicles. o Collects, processes, modifies and sorts molecules that are ready for transport in Golgi vesicles to other parts of the cell or out of the cell by: ▪ Secretion/exocytosis: fusion of vesicle with plasma membrane to release content. o Makes lysosomes, glycoproteins and functioning proteins.
Large central vacuole and tonoplast:
surrounded by partially permeable tonoplast, has cell sap (fluid) that consists of enzymes, sugars, waste products, pigments, mineral salts, oxygen, C02 and regulates osmotic properties.
TEM and SEM differences?
tem- electrons absorbed (transmit through the specimen) sem- electrons bounce off specimen (to show only 3D structure)
Nucleus (10μm):
the largest organelle surrounded by the double membraned nuclear envelope and is continuous with rough endoplasmic reticulum. o Nuclear pore: gaps in the nuclear envelope that allow exchange between the nucleus and cytoplasm. ▪ Substances leaving: mRNA (NO DNA)and ribosomes for protein synthesis. ▪ Substances entering: protein to help make ribosome, nucleotide, ATP, & some hormones. o Chromosome: contains the hereditary material DNA that is organised into genes which controls the activities of the cell and inheritance. o Nucleolus (0.2-0.5μm) one or more found (nucleoli) containing DNA and RNA, functioning to make ribosomes.
why do mitochondria appear different shapes in images?
viewed from different angles at different levels some cut transversely others cut through the middle of the cell (pg 14 in book)
