A2.2. Cell Structure Flashcards

Question

Distinguish between resolution and magnification.

Answer 1

Resolution is the ability to separate visually small objects that are very close together. However, magnification is just the amount of times larger an image is than the specimen.

Answer 2

The cell's ultrastructure- its individual organelles and plasma membrane.

Answer 3

Firstly, it cause significant damage to biological specimens, especially living cells. The interaction of electrons with the sample can lead to ionization, molecular bond breakage, and other forms of radiation damage, which can kill or alter the cells. Secondly, the equirement for Vacuum Conditions. However, living cells cannot survive in a vacuum, as it leads to dehydration and collapse of the cell structure.

Answer 4

Technique--->Flash-freezing of cell, then exposes electrons to high resolution images, producing a 3D shape. Advantages--> Some materials such as biological molecules are not comaptible with high-vacuum conditions and high intensity electron beams. Hence advantages of CRYOGENIC EM, include- 1) There is no evaporation of water around the molecule as cryogenic EM uses frozen samples. 2) Specimen is not destroyed and is alive and frozen, all possible with a lower intensity electron beam.

Answer 5

FIRSTLY, biological material i INSTANTLY FROZEN in LIQUID Nitrogen. Then, it is BROKEN UP IN A VACUUM. Secondlly, the EXPOSED SURFACE LOSES SOME ICE, hence being described as ETCHED. Thirdly, a CARBON REPLICA of surface is made, COATED with HEAVY METAL to strenghen before examination under an electron micrograph Lastly, resulting electron micrograph is produced by freeze etching. 1) FROZE< LIQUID NITROGEN, VACUUM 2) ETCHED 3) CARBON REPLICA, HEAVY METAL COATING. 4) FREEZE ETCHING PRODUCES FINAL PRODUCT

Answer 6

It provides a PLANAR VIEW OF THE MEMBRANE with VERY HIGH RESOLUTION DETAILS. Secondly, The DISTRIBUTION and organization of membrane proteins and other molecules are rendered visible. (Therefore, when we are shown an image where we can bsee the location and distribution of protein, it is a freeze fracture technique. )

Answer 7

Cryogenic microscpy, where we flash freeze biological material without killing the specimen, is often used to reveal HOW PROTEINS FUNCTION, how they MALFUNCTION with disease and HOW to target them with drugs.

Answer 8

Used in X-Ray crystallography, the structure of DNA was discovered in this way by Rosalind Franklin.

Answer 9

Cryogenic electon microscopy uses flash-freezing methods while freeze fracture methods employ instant freezing in liquid nitrogen

Answer 10

Fluorescent dyes absorb & then emit light at a longer wavelength. They can be used to bind to biomolecules (DNA, proteins) to reveal their cellular locations. There are two sets of filters, The FIRST SET filters the light BEFORE it reaches the specimen. It passes ONLY those wavelengths that excite the SPECIFICALLy chosen fluorescent dye. The SECOND SET of filters BLOCS OUT LIGHT and passes ONLY those wavelengths emitted WHEN THE FLUORESCENT DYE FLUORESCES. Dyed objects show up in bright colours on a dark background.

Answer 11

. Firstly, Other dyes can be used with ANTIBODY molecules which then BIND SELECTIVELY to targeted biomolecules e.g. DNA showing the distribution in the cell. This is used to explin e.g. structure of cell's plasma membrane and mechanisms by which muscles contract. Secondly, Can be used in IMMUNOFLUORESCENCE. Immunofluorescence uses ANTIBODIES which are CHEMICALLY LABELLED with FLUORESCENT DYES to be visualised under a lught microscope. Antibodies ATTACH to AFFECTED CELLS AND DYES INDICATE WHICH CELLS ARE MARKED THIS WAY. This is used for CANCER DIAGNOSIS when the cancer is present only at a small sampe of tissue.

Answer 12

The smooth endoplasmic reticulum consists of a tubular membrane network that is branched. The smooth-endoplasmic reticulum manufactures lipids, phospholipids and steroids (acronym LPS). Furthermore, in muscle cells, the smooth endoplasmic reticulum stores calcium ions.

Answer 13

Microtubules are straight, unbranched, thickest, hollow cylindrical fibres (25 nm in diameter). They are made up of tubulin (globular protein), capable of reassembling & dismantling Functions: control the movement of chromosomes in cell division, guide the movement of secretory vesicles from Golgi apparatus to plasma membrane Provide mechanical support, maintains cell shape. Microfilaments- each filament consists of a twisted double chain of actin (globular proteins) Function: resist tension to maintain & change cell shape, involved in cleavage furrow formation during cell division, regulates cell motility particularly during muscle contraction

Answer 14

Lysosomes contains hydrolytic enzymes to breakdown foreign particles (phagocytosis) or worn out organelles (auto-phagy). They are also involved in programmed cell death. The golgi apparatus synthesizes hormones and enzymes which it packages into vesicles (GA, SHE, PIV acronym). Abundant in metabolically active cells, i.e. secretory cells. The rough endiplasmic reticulum synthesizes proteins, The RER has many metabolically active cells. Site of synthesis, folding & post-translational modification of secretory proteins, e.g. digestive enzymes. The SER is involved in synthesizing, lipids, phospholipids and steroids.

Answer 15

When filled with water, it pushes the cytoplasm against the cell wall, creating turgor pressure to maintain plant tissue rigidity. Chemicals such as pigments (betalains), carbohydrates, fats & proteins can be stored. The interior is slightly acidic (pH 5.0) contains hydrolase enzymes to break down waste material

Answer 16

Nuceloid, plasmid, pilli and flagellum. A plasmid is a small circular DNA molecule found in bacteria and some other microscopic organisms. Plasmids are physically separate from chromosomal DNA. The pilli are for reproduction and the flagella propel movement of the cell

Answer 17

Both fungi and plants have a cell wall while animals do not. The fungi cell wall is made of chitin while the cell wall of plants is made of cellulose. Animals, Plants and fungi all have a vacuole. However, the vacuole is smaller in animals is may be temporary in contrast to plants where it is permanent and serves the role of maintaining turgor pressure. Fungi also have a large vacuole. Plastids are ONLY found in plants/ Similarly, centrioles are ONLY found in animals. Some animals have cilia, while cilia does not exist in plants or fungi. Cilia is used to move the ovum in the ovary duct to the uterus. All 3 types of organisms have flagella, to some extent. For instance, the sperm cell has 1 flagellum to propel itself to the egg. Cell walls are tough layers, outside of the plasma membrane. The main component in plant cell walls is cellulose and in fungal cells it is chitin. Animal cells do not have cell walls, which allows them to take in food by endocytosis but makes them vulnerable to bursting if too much water enters by osmosis. Vacuoles are single-membrane sacs of fluid in the cytoplasm. There is often a large permanent vacuole in cells of fungi and plants, used for storage of substances and pressurising the cells, maintaining turgor pressure in plants. Two types of small temporary vacuoles occur in some animal cells but not in plant cell s or fungus cells: contractile vacuole that expels access water by exocytosis and food vacuoles tat digest food or digest pathogens taken in by endocytosis. Plastids are a family of double-membraned organelles. Plant cells have varied types of chloroplasts (for photosynthesis) and amyloplasts (amyloplasts store starch). Animals and fungus cells have no plastids. Centrioles: Centrioles are organelles composed of a 9+2 arrangement t of microtubules, They are used in animal cells to organise assembly of a spindle of microtubules during mitosis and meiosis. Cilia and flagella are whip-like structures with a 9+2 arrangement of microtubules inside and plasma membrane on the outside, They protrude from the cell and generate movement by a beating action. Sone types of animal cell have many cilia, which are small and move fluids adjacent to cell. Male gametes (sperm) in animals have a single flagellum (tail, which is much longer than cilia and causes sperm to move. Some plants, including ferns and mosses, have motile male gametes with a flagellum- but conifers, flowering plats and almost al fungi fo not. A2.2.8- Differences in eukaryotic cell structure between animals, fungi and plants Include presence and composition of cell walls, differences in size and function of vacuoles, presence of chloroplasts and other plastids, and presence of centrioles, cilia and flagella.

Answer 18

Resolution (resolving power) of a microscope is its ability to separate visually small objects that are very close together. If two separate objects cannot be resolved, they are seen as one object. However, magnification is simply the degree to which the size of an image is increased compared to the actual size of the specimen.

Answer 19

X 10 000 Image= actual photo size X magnification Actual size= Image divide by magnification Magnification= Image size divide by actual size A2.2.2- Microscopy Skills Application of skills: Students should have experience of making temporary mounts of cells and tissues, staining, measuring sizes using an eyepiece graticule, focusing with coarse and fine adjustments, calculating actual size and magnification, producing a scale bar and taking photographs.

A2.2. Cell Structure Flashcards

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