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Z A level Biology > The Cell > Flashcards

The Cell Flashcards

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1
Q

What is the nuclear envelope?

A
  • Two membranes which surround the nucleus (the nucleus is the largest cell organelle)
  • The outer membrane of the nuclear envelope is continuous with the endoplasmic reticulum
  • The two membranes; situated closely together, that surround the nucleus; the envelope is perforated with nuclear pore
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2
Q

What are nuclear pores, and what is their function?

A
  • Nuclear pores are small pores located on the nuclear envelope
  • They are pores found in the nuclear envelope which control the change of material, e.g. mRNA, between the nucleus and the cytoplasm
  • They allow and control the exchange between the nucleus and the cytoplasm
  • Examples of substances leaving the nucleus through the nuclear pores include mRNA and ribosomes for protein synthesis
  • Example of substances entering through the nuclear pores are proteins to help make ribosomes, nucleotides, ATP and some hormones
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3
Q

What is the function of the nucleolus?

A
  • This makes ribosomes, using the information in its own DNA
  • Made of loops of DNA from several chromosomes
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4
Q

What is chromatin?

A
  • Chromosomes in a loosely coiled state

- Chromosomes contain DNA, which is organised into genes

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5
Q

What is the Endoplasmic Reticulum (ER)?

A
  • An extensive system of membranes running through the cytoplasm
  • The membranes form an extended system of flattened compartments called sacs, spreading throughout the cell
  • Processes can take place inside these seas operate from the cytoplasm
  • The sac can be interconnected to form a complete system (reticulum)
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6
Q

Describe the Rough ER

A
  • Covered with many tiny ribosomes
  • Ribosomes are the site of protein synthesis, and they can be found free in the cytoplasm as well as on the rough ER
  • Ribosomes (80S in the cytoplasm and 70S in chloroplasts and mitochondria)
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7
Q

Describe the Smooth ER

A
  • It lacks ribosomes

- It makes lipids and steroids, such as cholesterol and the reproductive hormone oestrogen and testosterone

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8
Q

Describe the Golgi body

A
  • The Golgi body is a stack of flattened sacs, and the stack is constantly being formed at one end from vesicles which bud off from the ER and broken down again at the other end to form Golgi vesicles
  • The stack of sacs together with the associated vesicles is referred to as the Golgi apparatus or Golgi complex
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9
Q

What is the function of the Golgi body?

A

-The Golgi body collects, processes and sorts molecules (particularly proteins form the rough ER), ready for transport in Golgi vesicles either to other parts of the cell, or out of the cell (secretion)

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10
Q

What is the cytoplasm?

A

-An aqueous material, varying from a fluid to a jelly-like consistency

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11
Q

What are lysosomes?

A
  • Lysosomes are spherical sacs, surrounded by a single membrane and having no internal structure
  • They contain digestive (hydrolytic) enzymes which must be kept separate from the rest of the cell to prevent damage from being done
  • They are responsible for the breakdown (digestion) of unwanted structures such as old organelles or even whole cells
  • 0.1-0.5 micrometers in diameter
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12
Q

Describe the structure of mitochondria

A
  • They are surrounded by two membranes (an envelope)
  • The inner of these is folded to form finger-like cristae which project into the interior solution or matrix
  • The space between the two membranes is called the intermembrane space
  • Small circular DNA
  • 1 micrometer in dimater
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13
Q

What is the function of mitochondria?

A
  • They carry out aerobic respiration
  • They are involved in the synthesis of lipids
  • Most of the energy realised is transferred to molecules of ATP
  • The reactions of respiration take place in solution in the matrix and in the inner membrane (cristae)
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14
Q

Describe the cell surface membrane

A
  • Extremely thin (about 7nm)
  • Has three layers, described as a trilaminar appearance
  • The membrane is partially permeable and controls exchange between the ell and its environment
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15
Q

What are microvilli?

A
  • They are finger-like extensions of the cell surface membrane, typical of certain epithelial cells (cells covering surfaces of structures)
  • They greatly increase surface area of the cell surface membrane
  • This is useful for example, for absorption in the gut and reabsorption in the proximal convoluted tubules of the kidney
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16
Q

What are microtubules and microtubule organising centres (MTOCs)?

A
  • Microtubules are long, rigid, hollow tubes found in the cytoplasm
  • Together with actin filaments and intermediate filaments, they may up the cytoskeleton, an essential structural component of cells which helps to determine cell shape
  • They have a mechanical function of support and are involved in intracellular transport system and membrane bound organelles are held in place by the cytoskeleton
  • Microtubules are made from the protein, tubulin
  • The assembly of microtubules from tubulin molecules is controlled by special locations in cells called microtubule organising centres (MTOCs)
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17
Q

What are centrioles?

A
  • They lie close together and at right angles to each other in a region known as the centrosome
  • Centrioles and other centrosome are absent from most plant cells
  • A centriole is a hollow cylinder about 500nm long formed from a ring of short microtubules and each centriole contained nine triplets of microtubules
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18
Q

Describe chloroplasts

A
  1. They are surrounded by two membranes, forming the chloroplast envelope
  2. Chloroplasts replicate themselves independently of cell division by dividing into two
  3. They have their own protein synthesising machinery, including 70S ribosomes and a circular strand of DNA
  4. They contain chlorophyll which is the green pigment which absorbs light during photosynthesis
  5. Small circular DNA
    - Diameter 3-10 micrometer
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19
Q

What are the functions of chloroplasts?

A

-Chloroplasts’s main function is to carry out photosynthesis

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20
Q

Where is ATP produced?

A
  • In mitochondria and chloroplasts
    1. Most of the energy released during respiration is transferred to molecules of ATP (adenosine triphosphate) and it is the energy carrying molecules found in all living cells
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21
Q

What happens to the ATP after it leaves the mitochondrion cell?

A
  1. ATP is a small, soluble molecule
  2. It spreads rapidly to all parts of the cell where energy is needed
  3. Its energy is released by breaking the molecule down to ADP (adenosine diphosphate)
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22
Q

What are some of the key structural features of typical prokaryotic cells as seen in a typical bacterium?

A
  1. Unicellular
  2. 1 - 5 micrometers diameter
  3. Peptidoglycan cell walls
  4. Lack of membrane-bound organelles
  5. Naked circular DNA
  6. 70S ribosomes
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23
Q

What are the diameters of prokaryotes against eukaryotes?

A
  1. Prokaryotes: average dimatere of cell is 0.5-5 miumeters

2. Eukaryotes: cells commonly up to 40 miumeters and commonly 1000-10000 times the volume of prokaryotic cells

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24
Q

How is the DNA organised in prokaryotes against eukaryotes?

A
  1. Prokaryotes: DNA is circular and lies free in the cytoplasm
  2. Eukaryotes: DNA is not circular and is contained in a nucleus (the nucleus is surrounded by an envelope of two membranes)
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25
Q

What is the DNA like in prokaryotes against eukaryotes?

A
  1. Prokaryotes: DNA is naked

2. Eukaryotes: DNA is associated with protein, forming structures called chromosomes

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26
Q

What are the ribosomes like in prokaryotes against eukaryotes?

A
  1. Prokaryotes: Slightly smaller (70S) ribosomes (about 20nm diameter) than those of eukaryotes
  2. Eukaryotes: Slightly larger (80S) ribosomes (about 25 nm diameter) that those of prokaryotes
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27
Q

Is there an ER in prokaryotes against eukaryotes?

A
  1. Prokaryotes: no ER present

2. Eukaryotes: ER present, to which ribosomes may be attached

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28
Q

Describe the organelles in prokaryotes against eukaryotes?

A
  1. Prokaryotes: very few cell organelles (no separate membrane-bound compartments unless formed by infolding of the cell surface membrane)
  2. Eukaryotes: many types of cell organelle present (extensive compartmentalisations and division of labour):
    -some organelles are bounded by a single membrane, e.g. lysosomes, Golgi body, vacuoles
    some are bounded by two membranes (an envelope), e.g. nucleus, mitochondrion, chloroplast
    -some have no membrane, e.g. ribosomes, centrioles, microtubules
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29
Q

Is there a cell wall in prokaryotes against eukaryotes?

A
  1. Prokaryotes: cell wall present, wall contained murrain, a peptidoglycan (a polysaccharide combined with amino acids)
  2. Eukaryotes: cell walls sometimes present e.g. in plants and fungi, contains cellulose or lignin in plants, and chitin (a nitrogen-containing polysaccharide similar to cellulose) in fungi
30
Q

What are some of the key features of viruses?

A
  • Non-cellular structures
    1. They consist of a self-replicating molecules of DNA or RNA which acts as its genetic code
    2. A protective coat of protein molecules (each of which is called a capsomere) which make up the protein coat (or capsid)
  • They range in size from about 20nm-300nm (about 50 times smaller on average than bacteria)
  • All viruses are parasitic as they can only reproduce by infecting and taking over living cells; the virus DNA or RNA takes over the protein synthesising machinery of the host cell, which then helps to make new virus particles
31
Q

What is the cell wall?

A
  1. Contains fibres of cellulose and it gives the cell a definite shape
  2. It prevents the cell from bursting when water enters by osmosis, allowing large pressures to develop inside the cell
  3. They are feely permeable, allowing free movement of molecules and ions through to the cell surface membrane
32
Q

Describe the plasmodesmata

A
  1. Plants cells are linked to neighbouring cells by means of fine strands of cytoplasm called plasmodesmata
  2. These pass through pore-like structures in their walls
33
Q

What is a large permanent vacuole?

A
  • Mature plant cells often possess a large permanent, central vacuole
  • The fluid in the vacuole is a solution of pigments’ enzymes,sugars and other organic compounds (including some waste products), mineral salts, oxygen and carbon dioxide
  • Vacuoles help to regulate the osmotic properties of cells as well as having a wide range of other functions e.g. the pigments which colour the petals of certain flowers and parts of some vegetables, such as the red pigment of beetroots, may be located in vacuoles
34
Q

What is the tonoplast?

A
  1. The plant vacuole is surrounded by a membrane, the tonoplasts, which controls the exchange between the vacuole and the cytoplasm
35
Q

What is resolution?

A

Resolution is the ability to distinguish between two objects very close together; the higher the resolution of an image, the greater the detail that can be seen

36
Q

What is magnification?

A

Magnification if the number of times greater that an image is that the actual object

37
Q

How do you work out magnification?

A

magnification = observed size of image / actual size

38
Q

Describe a light microscope

A
  1. The maximum resolution of a light microscope of 200nm, therefore if two points or objects are closer together than 200nm they cannot be distinguished as separate
  2. It is possible to take a photograph (a photograph taken with a light microscope is known as a light micrograph or a photomicrograph) and to magnify (enlarge) it, but we see no more detail, in other words, we do not improve resolution, even though we often enlarge photographs because they are easier to see when larger
  3. With a microscope, magnification up to the limit of resolution can reveal further detail, but nany further magnification increases blurring as well as the size of the the image
39
Q

Describe an electron microscope

A
  1. A resolution of 0.5 nm can be obtained (400 times better than a light microscope)
  2. Two types; a transmission electron microscope )TEM) or scanning electron microscope (SEM)
40
Q

What is a transmission electron microscope?

A
  • A beam of electrons is passed through the specimen before being viewed
  • Only those electrons which are transmitted (pass through the specimen) are seen
  • This allows us to see thin sections of specimens, and thus to see inside cells
41
Q

What is a scanning electron microscope? What are the advantages and disadvantages?

A
  • The electron beam is used to scan the surfaces of structures, and only the reflected beam is observed
  • Advantages of this microscope:
    1. Is that surface structures can be seen, and since great depth of filed is obtained, much of the specimen is in focus at the same time and a 3D appearance is achieved
  • Such a picture would be impossible to obtain with a light microscope even using the same magnification and resolution, because you would have to keep focusing up and down with the objective lens to see different parts of the specimens
  • Disadvantage of SEM:
    1. It cannot achieve the same resolution as a TEM; using a SEM, resolution is between 3nm and 20nm
  • Look at sheet!
42
Q

What is contrast?

A

The ability to distinguish the specimens, or part of it, from the background

43
Q

Why is the resolution of an electron microscope better than light?

A

When using light rather than electron you are limited by the wavelength of light

44
Q

What is the cell surface membrane?

A

A very thin membrane (about 7nm diameter) surrounding all cells; it is partially permeable and controls the exchange of material between the cell and its environment

45
Q

What is the nucleus?

A

A relatively large organelle found in eukaryotic cells, but absent from prokaryotic cells; the nucleus contain she cell’s DNA and therefore controls the activities of the cell

46
Q

What is chromatin?

A

The loosely coiled form of chromosomes during interphase of the cell cycle; chromatin is made of DNA and proteins and is visible as loosely distributed patches or fibres within the nucleus when stained

47
Q

What is the nucleolus?

A

A small structure, one or more of which is found inside the nucleus; the nucleolus is usually visible as a densely stained body; its function to manufacture ribosomes using the information in its own DNA

48
Q

What is the Golgi apparatus?

A

An organelle found in eukaryotic cells the Golgi apparatus consists of a stack of flatted sacs, constantly forming at one up and breaking up into Golgi vesicles at the other end; Golgi vesicles carry their contents to other parts of the cell, often to the cell surface membrane for secretion; the Golgi apparatus chemically modifies the molecules it transports; for example, sugars may be added to proteins to make glycoproteins

49
Q

What are organelles?

A

A functionally fn structurally distinct part of the cell, e.g. ribosome or mitochondrion

50
Q

What are mitochondrion?

A

The organelle in eukaryotes in which aerobic respiration takes place

51
Q

What are chloroplasts?

A

The photosynthetic organelle in eukaryotes

52
Q

What are granum (sing)?

A

A stack of circular thylakoids in a chloroplast

53
Q

What are chlorophyll?

A

A green pigment responsible for for light capture in photosynthesis in algae and plants

54
Q

What is plasmodesmata?

A

A pore-like structure found in plant cell walls; plasmodesmata of neighbouring plant cells line up to form tube-like pores through the cell walls allowing the controlled passage of material from one cell to the other; the pore contain ER and are lined with eh cell surface membrane

55
Q

What is a vacuole?

A

An Organelle found in eukaryotic cell; a large permanent central vacuole is typically feature of plant cells, where it has a variety of unctions, including storage of biochemicals such as salts, sugar and waste products; temporary vacuoles, such as phagocytic vacuoles (also known as phagocytic vesicles) may form in animal cells

56
Q

What is a tonoplast?

A

A partially permeable membrane that surrounds plant vacuoles

57
Q

What is the endosymbiont theory?

A
  1. Mitochondria and chloroplasts contain ribosomes which are slightly smaller that those in the cytoplasm and are the same size as those found in bacteria
  2. Mitochondria and chloroplasts contains small, circular DNA molecules also like those found in bacteria
  3. Mitochondria and chloroplasts are in effect, ancient bacteria which now live inside the larger cells typical of animals and plants
    - This is known as endosymbiont theory
    - The DNA and ribosomes of mitochondria and chloroplasts are still active and responsible for the coding and synthesis of certain vital proteins, but mitochondria and chloroplasts can no longer live independently
58
Q

What do all eukaryotic cells possess?

A

A nucleus containing one or more nucleoli and DNA, the DNA is linear and bound to proteins to form chromatin

59
Q

How do you figure out magnification?

A

magnification = observed size of image / actual size of image

60
Q

Describe a light microscope

A
  • Resolution: maximum 200nm (two points closer than this cannot be distinguished as separate) (roughly limit of resolution is half the wavelength of the radiation used to view)
  • If object transparent light pass through so need to be stained
  • Magnification: x1500
  • Coloured dyes
61
Q

How big are ribosomes?

A

25nm diameter (can’t be seen using light)

62
Q

Describe electron microscope

A
  • Very short wavelength
  • Can be focus by electromagnet as negatively charged
  • Resolution: 0.5nm
63
Q

What is a scanning electron microscope?

A
  • The electron beam scan surfaces of structure so only reflected beam is observed
  • SEn restitution is 3nm-20nm so not as good as TEM
  • Mag: x100,000
  • Specimen coated with carbon or gold
64
Q

What is a transmission electron microscope?

A
  • Beam of electrons passes through the specimen and only those electrons transmitted are seen
  • So can see thin sections of specimen and inside cells
  • Mag: x250,000
  • Specimen impregnated with heavy metals
65
Q

Compare electron and light microscope

A
  1. Electron Adv: 400 times better resolution, 3D image (only with sem) and transmission or scanning available, and high magnification x250,000
    Electron Disadvantage: more prep or specimen needed, expense, monochromatic images, cannot view living specimen
  2. Light Adv: specimen can be alive (electron need vacuum), cheaper, worse magnification, coloured image, unaffected by magnetic fields
    Light Dis: staining can lead to artefacts, 2D image, magnification limited (x1500)
66
Q

What are three structural features present in a mesophyll leaf cell not present in a prokaryotic cell?

A
  • Chloroplasts
  • Nucleolus
  • RER
  • Cellulose cell wall
  • Golgi body
67
Q

Why is light microscope better than electron?

A
  • Cells killed
  • Vacuum
  • Light microscope can have water on the slide
  • More readily available for use
68
Q

What does DNA do?

A
  1. Codes for proteins e.g. rubisco

2. Transcription

69
Q

What is the Calvin cycle and photolysis affected by?

A
  1. Calvin Cycle: carbon dioxide conc, temperature

2. Photolysis: light intensity

70
Q

What does reduced NADP do in the light independent stage?

A
  • GP converted to TP

- Reduces/donates hydrogen

Z A level Biology (15 decks)

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