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Biology > 1. Cell Structure > Flashcards

1. Cell Structure Flashcards

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1
Q

How to prepare a wet mount slide (using an epidermis from the scale leaf of an onion)?

A
  • Use forceps to peel of a piece of epidermal tissue (one cell think) from the concave side (inner side) onto the centre of a microscope slide
  • Add a drop of water and use forceps/mounted needle to help spread out the tissue to obtain a flat layer with no creases
  • Place a coverslip at an angle to the slide and move it slowly towards the tissue until water runs under the edge of the slip. Use the forceps/mounted needle to lower the coverslip onto the tissue at an angle to prevent air bubbles forming
  • Add a drop of iodine solution to the slide against one edge of the coverslip
  • Place a piece of filter paper against the other side of the coverslip so that it can soak up some of the water and “pulls” some of the iodine solution to stain a portion of the epidermis (irrigation)
  • Carefully blot up any fluid on top of the coverslip before viewing using the microscope
    *if there are any air bubbles, they may be removed by gently tapping the coverslip with the other end of the mounted needle
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2
Q

What structures in plant and animal cells are not visible using a light microscope and why?

A
  • Cell surface membrane of animal cells
  • Tonoplast of plant cells
  • They are too thin to interfere with the light waves and so cannot be seen directly but with the use of stains these structures can be observed indirectly
  • To see the mitochondrion and Golgi body a magnification of around x1500 is required
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3
Q

How to draw cells?

A
  • Use the available space, but leave room for labels with ruled label lines
  • Use an HB pencil to produce thin, clearly visible lines
  • Draw continuous lines
  • Draw complete cells and include any structures that are visible (do not shade)
  • Make sure that the proportions of cell structures are the same as in the cells you are viewing
  • Label the cell structure/annotate
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4
Q

How to use an eyepiece graticule and stage micrometer scale?

A
  • The graticule is a glass disc which is placed in the eyepiece of a microscope
  • A scale is etched on the disc which is typically 10mm long and is divided into 100 subdivisions
  • Needs to be calibrated first for a particular objective lens
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5
Q

How to calibrate the eyepiece graticule?

A
  • Need to use a stage micrometer which has an etched scale of 2mm long and its smallest subdivisions are 0.01 mm (10um)
  • When the eyepiece graticule scale and stage micrometer scales are lined up, the distance between the divisions on the eyepiece graticule can be calculated:
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6
Q

How to calculate eyepiece graticule?

A
  • For example, on the micrometer scale, 10 units are equivalent to 40 units on the graticule scale
  • Therefore, one unit on the micrometer scale equals 4 units on the graticule scale
  • As each unit on the micrometer scale is 10 um, each unit on the graticule equals 10/4=2.5 um
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7
Q

What is magnification and how to calculate it?

A

Magnification- the number of times larger the image is than the actual size of the cellular material
- Magnification beyond x1500 with a light microscope does not provide any more detail, whereas with an electron microscope it is possible to obtain clear images at magnifications up to x500 000

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8
Q

What is resolution?

A

Resolution- the ability to distinguish between two points
- The minimum distance apart that two objects can be in order for them to appear as separate items
- The higher the resolution the clearer, sharper and more detailed the image produced is

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9
Q

What are the features of the nucleus?

A
  • Usually spherical and is between 10 and 20 um in diameter
  • Contains 4 parts: nuclear envelope, nuclear pores, chromatin and nucleolus
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10
Q

Features of nuclear envelope?

A

 Double membrane that surrounds the nucleus
 Its outer membrane is continuous with the endoplasmic reticulum and ribosomes on its surface
 Controls the entry and exit of materials

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11
Q

Features of nuclear pores?

A
  • Allow the passage of large molecules (mRNA) out of the nucleus, but are too small to allow to allow DNA to leave
  • Around 3000 pores in each nucleus and are 40-100 nm in diameter
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12
Q

Features of nucleolus?

A
  • Nucleolus
  • Small spherical region/regions that manufactures rRNA and assembles the subunits of the ribosome
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13
Q

Features of chromatin?

A
  • The diffuse, thread-like form that chromosomes take up when the cell is not dividing
  • When the cell divides the chromatin condenses into chromosomes
  • Chromatin is composed of DNA complexed with histone proteins
  • Nucleoplasm surrounds it
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14
Q

Functions of the nucelus?

A
  • Contains genes
  • Produces ribosomal subunits
  • Controls protein synthesis (through the production of mRNA) by switching genes on/off
  • Location for DNA replication before a cell divides
  • With its envelope the nucleus protects the DNA from the rest of the cell
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15
Q

What are the features of chloroplasts and its functions?

A
  • Function is photosynthesis
  • Found in plant cells
  • Flat discs that are usually 3-10 um in diameter and 1 um thick
  • Contains 4 parts: chloroplast envelope, grana, stroma and starch grains
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16
Q

Functions of chloroplast envelope?

A

Double membrane which controls the entry and exit of substances

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17
Q

Functions of grana?

A
  • Each is made up thylakoids (stack of flattened sacs)
  • The thylakoid membranes contain chlorophyll molecules which absorb light energy in the light-dependent stage and produce ATP
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18
Q

Function of stroma?

A
  • A colorless, jelly-like matrix which contains enzymes necessary for light independent stage
  • Lipid globules are present
  • Small circular DNA molecules and 70S ribosomes which allow some chloroplast proteins to be made are present
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19
Q

Functions of starch grains?

A
  • Act as temporary stores of glucose which is produced during photosynthesis
20
Q

What are the features of mitochondria and its functions?

A
  • Function is aerobic respiration as they supply energy to the cell, because they synthesize (produce) ATP molecules from carbohydrates and other respiratory substrates (fatty acids)
  • Present in all but a few eukaryotic cells
  • Usually rod shaped, 1-7 um in length and 0.5-1,0 um in diameter
  • Made up of 3 parts: double membrane, cristae, matrix
21
Q

Function of double membrane?

A

Surrounds the organelle and controls the entry and exit of substances

22
Q

Function of cristae?

A
  • Infoldings of the inner membrane and some extend across the mitochondrion
  • Contain enzymes involved in aerobic respiration
  • Provide large surface area for oxidative phosphorylation which results in the synthesis of ATP molecules
  • The size and number of cristae increases in cells that have a high level of metabolic activity and therefore need a good supply of ATP (liver and muscle cells)
23
Q

Function of matrix?

A
  • Thick fluid containing enzymes involved in Krebs cycle
  • Small circular DNA (mtDNA) and 70S ribosomes present (means mitochondria can produce some of its own proteins
24
Q

What are the features of the endoplasmic reticulum?

A
  • Extensive, 3D system of sheet-like membranes spreading through the cytoplasm
  • ER comprises a network of tubules and flattened sacs enclosed by single membranes
  • 2 types: smooth and rough
25
Q

What are the features of ribosomes and their functions?

A
  • Small spherical structures found in all cells
  • May occur in cytoplasm or be associated with the RER
  • 2 types: 70S and 80S
  • 80S- found in eukaryotic cells and are 22nm in diameter
  • 70S- found in prokaryotic cells and in the mitochondria and chloroplasts of eukaryotic cells. 17 nm in diameter.
  • Each ribosome has 2 subunits: large and small and each contains rRNA and protein
  • Site of protein synthesis
26
Q

What are the features of Golgi bodies?

A
  • Occurs in most eukaryotic cells
  • Consists of a stack of membranes which make up flattened sacs/cisternae (curved appearance) and associated hollow vesicles
  • Proteins arriving from RER/SER are passed through the Golgi body in a strict sequence starting at one cis of the complex and finishing at the trans
  • The Golgi processes these molecules, modifying them so that they will function correctly in their final destination
  • Also labels them so that they can be sorted and sent to their correct destinations
  • Once sorted the modified proteins and lipids are packaged into Golgi vesicles, which are regularly pinched off from the ends of the Golgi cisternae
27
Q

What are the functions of the Golgi body?

A
  • Modification and final processing of proteins and lipids
  • Packaging of proteins or lipids, forming Golgi vesicles
  • Formation of primary lysosomes
  • Golgi vesicles can be moved towards the cell surface membrane along microtubules and some vesicles fuse with the membrane and release their contents to become part of the cell surface membrane, while others fuse and release their contents to the external environment
28
Q

What are the features of lysosomes?

A
  • From 50nm to 700 nm in size
  • Spherical organelles bound by a single membrane that protects the rest of the cell from acid hydrolases (hydrolytic enzymes such as proteases, lipases and nucleases) contained within them
  • The enzymes are not active until the lysosome fuses with another membrane-bound sac containing the material that needs to be broken down
  • Some membrane-bound sacs are formed within a cell while others are phagosomes which are formed when the cell surface membrane invaginates to enclose bacterial or other foreign material to destroy it
  • Some cells are phagocytes which specialize in engulfing bacteria or other foreign material to destroy them
29
Q

What are the functions of lysosomes?

A
  • Digestion of old/worn out organelles (such as mitochondria) which allows the re-use of chemicals by the cell
  • Digestion of bacteria, foreign material or cell debris
  • Digestion of cells after autolysis
  • Release of hydrolytic enzymes to the outside of the cell to destroy material around the cells
30
Q

What are the features of the cell surface membrane?

A
  • Defines the cell and encloses the cell contents
  • It is a phospholipid bilayer containing proteins (allows some substances that are soluble in water to pass through) and prevents the exit or entry of some substances based on their size and solubility in lipids and is therefore described as partially permeable
31
Q

What are the functions of the cell surface membrane?

A
  • It is a boundary and forms a barrier between the cytoplasm and external environment and protects cell from harmful substances
  • Controls the movement of substances in and out of the cell
  • Important in cell recognition as it has molecules on its surface that are recognized by other cells
  • Contains receptor sites which bind specific hormones, neurotransmitters and other cell signaling molecules
  • Helps cells to form tissues by cell-to-cell adhesion
  • Contains enzymes to catalyse specific reactions
32
Q

What are the features and functions of microvilli (animal cells only)?

A
  • Tiny projections around 1 um long that extend outwards on the cell surface membrane
  • Vastly increase the surface area over which absorption/secretion can take place
33
Q

What are the features cilia (animal cells only)?

A
  • Hair-like structures that extend from a basal body at the surface of some animal cells
  • Covered in cell surface membrane and are constructed of microtubules (in cross section there is a 9+2 microtubule arrangement)
  • They are motile and have a whip-like movement
  • Each ciliated cell has many cilia that are able to move in a synchronous rhythm
34
Q

What are the functions of cilia?

A
  • To move substances across the surface of cells (such as mucus in the respiratory airways)
  • Their way-like action helps to move the egg cell and sperm in the fallopian tubes
35
Q

What are the features of centrioles and microtubules?

A
  • Found in almost all animal cells as well in the cells of some algae and fungi (not in the cells of higher plants)
  • Hollow cylinders 0.5 um in length and 0.2 um in diameter, made up of 9 sets of 3 microtubules
  • There are 2 centrioles in an animal cell which lie at right angles to one another near to the nucleus
  • Microtubules are composed of tubulin (globular protein)
36
Q

What are the functions of centrioles and microtubules?

A
  • Centrioles have a role in organizing microtubules to form spindle fibers during nuclear division
  • The basal body of the cilium is a modified centriole which is responsible for organizing microtubules to form the cilium
  • Microtubules form part of the cytoskeleton in a cell and provides support and gives shape to the cell
  • Microtubules serve as a scaffold for the movement and positioning of organelles within the cell, including transport and Golgi vesicles
    *microtubules make up centrioles
37
Q

What are the features of cell walls (plant cells only)?

A
  • Consists of cellulose microfibrils which contain cellulose embedded in a matrix
  • Cellulose microfibrils have considerable strength and contribute to overall strength of cell wall
  • Cell wall contains hemicellulose and pectin (polysaccharides)
  • The middle lamella (thin layer) between adjacent cells cements adjacent cells together
38
Q

What are the functions of cell walls?

A
  • Provides mechanical strength in order to prevent cell lysis under turgid pressure (created by osmotic entry of water)
  • Gives mechanical strength to plant as whole
  • Allows water to pass along it therefore contributes to the movement of water through the plant
39
Q

What are the features and functions of plasmodesmata (plant cells only)?

A
  • Small, thin cytoplasmic strand are present crossing through cell walls
  • The channels through which they pass are lined with cell surface membrane and these connect the cytoplasm of adjacent cells for cell communication and allow substances to pass between them without having to pass through the cell wall or cell surface membrane (form part of the symplast pathway)
  • Mineral ions, dissolved solutes and cell signaling molecules also pass between cells via the plasmodesmata
  • Can be a single or complex channel
40
Q

What are the features of large permanent vacuoles (plant cells only)?

A
  • It is surrounded by a tonoplast (membrane) and contains cell sap
41
Q

What are the functions of large permanent vacuoles?

A
  • Stores water, ions, sugars and pigments
  • Pushes chloroplasts to the edge of the cell for photosynthesis and gives turgidity to the cell to help support it
  • Can serve as a store of waste substances
  • Hydrolytic enzymes can also be found in vacuoles and these break down waste metabolic products
42
Q

What are the features and functions of the tonoplast (plant cells only)?

A
  • Vacuolar membrane and has the same basic structure as the cell surface membrane
  • It serves as a barrier between the contents of the vacuole and the cytoplasm and has some control over which substances can enter and leave the vacuole.
43
Q

What is the protoplast (plant cells only)?

A
  • Refers to everything in the cell, excluding the cell
44
Q

What are the features of bacteria?

A
  • 0.1-5.0 um in diameter
  • Unicellular
  • Peptidoglycan cell wall
  • Circular DNA in the form of plasmids and are used as vectors
  • 70S ribosomes
  • Absence of organelles surrounded by double membranes (nucleus, chloroplasts and mitochondria)
  • Flagellum
  • Capsule
  • Cell surface membrane
  • Cytoplasm
  • Pili (hair-like projections for attachments to other cells)
45
Q

What are the features of a virus?

A
  • Non-cellular
  • Nucleic acid core (either DNA or RNA)
  • Capsid (protein coat) that surrounds the nucleic core and is made of repeating capsomeres which also contains glycoproteins which bind to receptor sites of host cells
  • Some viruses have an outer envelope made of phospholipids which gives it a more flexible shape and helps the virus attach to host cells for infection
46
Q
A

Biology (12 decks)

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