Eukaryotic cells Flashcards

Question

What are lysosomes and what do they do?

Answer 1

Small membrane bound vesicles containing digestive enzymes. They are used to break down unwanted chemicals, toxins, organelles or even whole cells, so that the materials may be recycled. They can also fuse with a feeding vacuole to digest its contents. Responsible for cell death - autolysis.

Answer 2

A network of protein fibres extending throughout all eukaryotic cells, used for support, transport and motility. It is attached to the cell membrane and gives the cell its shape, as well as holding all the organelles in position. There are 2 types of protein fibres (microfilaments and microtubules); each has a corresponding protein that can carry a cargo such as an organelle, chromosome or other cytoskeleton fibres along the fibre. They are responsible for chromosome movement in mitosis and the subsequent division of the cell, cytoplasmic streaming or cyclosis (in plants only), cilia and flagella movements, and muscle contraction.

Answer 3

A set of short microtubules ('9+2') involved in cell division. Before each division the centriole replicates itself and the two centrioles move to opposite ends of the cell, forming the spindle that organises and separates the chromosomes.

Answer 4

Long flexible 'tails' present in some cells and used for movement. They are surrounded by the cell membrane and are full of microtubules and motor proteins, so they are capable of complex swimming movements. There are two types: Flagellae - (no relation to the bacterial flagellum), are longer than the cell and there are usually one or two of them. Cilia - though identical in structure, are much smaller and there are usually many of them.

Answer 5

Small finger-like extensions of the cell membrane found in some animal cells (e.g. the epithelial cells of the gut and kidney), where they increase the surface area for absorption. They are just visible under the light microscope as the brush border.

Answer 6

A thick layer outside the cell membrane used to give a cell strength and rigidity. They consist of a network of fibres, which give strength but are freely permeable to solutes (unlike membranes). Plant cell walls are made mainly of cellulose, but also contain pectin, lignin and other polysaccharides. It is built up in layers with the middle lamella separating the cell wall of adjacent cells. There are often channels through plant cell walls called plasmodesmata, which link the cytoplasm of adjacent cells. Fungal cell walls are made of chitin. Animal cells do not have a cell wall.

Answer 7

Organelles that contain their own DNA (coding for about 50% of the organelle) and reproduce independently of the nucleus.

Answer 8

Mitochondria and chloroplasts.

Answer 9

Mitochondrial DNA mutates at a known, constant rate and is only inherited from the mother, so it can be used to track purely female genetic lines. In the same way, the Y chromosome is only passed on from father to son and so can be used to track the purely male genetic line.

Answer 10

Sausage shape organelles (2-5um long), where aerobic respiration takes place in eukaryotic cells. They are surrounded by a double membrane, the outer membrane is quite permeable but the inner membrane is highly folded into cristae, which give it a large surface area. It is studded with ATPase, the enzyme which is the main site of ATP synthesis. This is where the last stage of respiration - the ETC takes place. The space enclosed by the inner membrane is called the mitochondrial matrix and contains small circular strands Of DNA and 70S ribosomes. This is the site of the TCA or Kreb's cycle stage of respiration.

Answer 11

They are bigger and fatter than mitochondria (so settle first when cells are homogenised and centrifuged), chloroplasts are the site of photosynthesis, so are only found in the photosynthetic cells (plants and algae). Like mitochondria a double membrane encloses them, but they also contain membranes arranged in disks called thylakoids which contain chlorophyll and other photosynthetic pigments and carry out the light reactions of photosynthesis. The thylakoids are then stacked into piles called grana. The space between the inner membrane and the thylakoid is called the stroma - the site of the light-independent (or 'carbon-fixing') stage of photosynthesis. Chloroplasts also contain starch grains, 70S ribosomes and circular DNA.