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AQA Biology A-level > Cells > Flashcards

Cells Flashcards

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1
Q

the cell theory

A

all life on earth exists as cells, is a unifying concept in biology.

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2
Q

viruses are

A

acellular and nonliving

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3
Q

eukaryotic cells

A

animals, plant and fungal cells

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4
Q

prokaryotic cells

A

bacteria

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5
Q

cell surface membrane

A
  • very thin phospholipid bilayer surrounds the cell
  • controls exchange between cell and environment
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6
Q

nucleus

A
  • contains chromosomes (linear DNA strands associated with histone proteins) and one or more nucleoli
  • nuclear envelope has nuclear pores to control exchange between nucleus and cytoplasm
  • controls gene expresión and mediates the replication of DNA during cell cycle.
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7
Q

mitochondrion

A
  • smooth outer membrane
  • inner membrane highly folded into cristae
  • carries out aerobic respiration, which takes place in the matrix and on the cristae, and synthesises ATP.
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8
Q

ribosome

A
  • site of protein synthesis
  • 80S in eukaryotic cells
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9
Q

smooth endoplasmic reticulum

A
  • similar structure to RER, but no ribosomes
  • synthesises lipids, steroids and hormones
  • synthesises, stores, and transports carbohydrates.
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10
Q

rough endoplasmic reticulum

A
  • an extended system of membrane sacs
  • encrusted with ribosomes
  • synthesises proteins.
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11
Q

Golgi apparatus and Golgi vesicles

A
  • stacks of flattened membranes
  • modifies proteins
  • makes lysosomes
  • collects, processes, and sorts molecules that are then transported in Golgi vesicles to other parts of the cell or secreted out of the cell.
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12
Q

lysosome

A
  • a Golgi vesicle that releases lysozyme and contains other hydrolytic enzymes
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13
Q

permanent vacuole (in plants)

A
  • contains sap and supports the plant
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14
Q

cell wall (plants, algae and fungi)

A
  • composed mainly of cellulose in plants, chitin in fungi and cellulose and/or glycoproteins in algae.
  • provides strength whilst remaining permeable
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15
Q

chloroplasts (in plants and algae)

A
  • disc-like thylakoid membranes are arranged in stacks called grant
  • internal fluid called stroma
  • light-dependent reactions of photosynthesis take place on the thylakoid membranes and light-independent reactions in the stroma.
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16
Q

Prokaryotic cells are much smaller than eukaryotic cells and possess:

A
  • cytoplasm that lacks membrane-bound organelles
  • smaller ribosomes (70S)
  • no nucleus - have a circular loop of DNA that is free in cytoplasm, and has isn’t associated with proteins
  • a cell wall that contains murein, a glycoprotein

Most prokaryotic cells also have:
- plasmids
- capsule surrounding cell
- one or more flagella

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17
Q

Viruses are acellular and nonliving. The structure of virus particles includes:

A
  • genetic material (DNA or RNA)
  • protein capsid
    attachment protein.
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18
Q

magnification

A

number of times greater the size of the image is than the size of the real object.
M= I/O

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19
Q

resolution

A

ability to distinguish between 2 objects that are very close together - a higher resolution means more detail.

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20
Q

light microscope

A
  • uses light to form an image
  • lights that passes through or reflects the surface of the specimen is sees
  • magnification to 2000X
  • resolution to 200nm
  • living and non-living can be observed
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21
Q

transmission electron microscope (TEM)

A
  • uses electrons to form an image
  • electrons that pass through the specimen are detected
  • magnification to 1,000,000X
    -resolution to 0.2nm
  • only dead or non-living specimens can be used
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22
Q

scanning electron microscope (SEM)

A
  • uses electrons to form an image
  • electrons that are reflected from the surface on the specimen are detected.
  • magnification to 1,000,000X
  • resolution to 3-20nm
  • only dead or non-living specimens can be used.
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23
Q

Artefact in microscopy include:

A
  • trapped air bubbles
  • folds in thin slices of the specimen
  • chemical changes due to stains
  • contamination from other cells or tissue.
24
Q

stains are used to…

A

colour different components of cells.
- gives clear indication of what substances (such as starch) are present in the cell and how they are distributed.
- non-invasive and results can be viewed under light microscope

25
Q

cell fractionation and ultracentrifugation

A
  1. tissue is cut up and kept in cold, isotonic and buffered solution
  2. cut-up tissues further broken up in a homogeniser and large debris is filtered out
  3. homogenised tissue is spun in an ultracentrifuge at a low speed for 10 mins
  4. results of being spun in ultracentrifuge at low speed -> pellet and supernatant formed. Separates organelles etc from heaviest to lightest.
  5. sound in ultracentrifuge at medium speed
  6. spun in ultracentrifuge at high speed.
26
Q

prokaryotic cells divide by

A

binary fission

27
Q

eukaryotic cells have 2 different types of division:

A
  1. mitosis - parent cell divides to produce 2 genetically identical daughter cells.
  2. meiosis - parent cell divides to produce 4 genetically different daughter cells with half number of chromosomes.
28
Q

stages of the cell cycle

A
  1. interphase - occupies most cell cycle and is 3 step process: G1: proteins required for organelles are synthesised, S: DNA replication, G2: organelles grow and divide, ATP levels increase
  2. nuclear division - nucleus divides into 2 or 4 (PMAT)
  3. cell division - cytokinesis.
29
Q

prophase

A
  • chromosome thicken and shorten by supercoiling
  • nuclear envelop disappears
  • centrioles form a spindle network, separate and move to opposite poles of cell
30
Q

metaphase

A
  • chromosomes move to equator of cell
  • spindle fibres attach to centromeres
31
Q

anaphase

A
  • spindle fibres contract, separating sister chromatids
  • individual chromatids are pulled towards the poles
32
Q

telophase

A
  • nuclear envelope appears around each set of chromatids to form 2 new nuclei
  • chromatids uncoil and spindle fibres disintegrate
33
Q

mitotic index

A
  • proportion of cells in a population undergoing mitosis
  • Mitotic index = number of cells undergoing mitosis / total number of cells observed.
34
Q

uncontrolled, rapid cell division can lead to formation of

A

tumours and cancer

35
Q

virus replication

A

inject nucleic acid into a host cell. The infected host cell synthesises viral nucleic acid and proteins and assembles virus particles.

36
Q

binary fission

A
  1. replication of circular DNA and plasmids in cytoplasm
  2. division of cytoplasm to produce 2 daughter cells, each with a single copy of circular DNA and a variable number of copies of any plasmids.
37
Q

fluid-mosaic model

A
  • fluid: phospholipids move relative to each other
  • mosaic: proteins dotted between phospholipids are of various shapes and sizes, like a tile mosaic.
38
Q

phospholipids

A
  • form basic structure of bilayer membrane
  • flexible
  • prevent passage of water-molecules
  • passage of lipid-soluble molecules
39
Q

intrinsic proteins

A
  • soon bilayer
  • enzymes, carrier proteins, and channel proteins.
40
Q

extrinsic proteins

A
  • found on surface or embedded in 1 layer of membrane
  • provide mechanical support
  • in conjunction with glycolipids act as cell receptors for hormones and other molecules.
41
Q

glycoproteins

A
  • receptors for chemical signals
  • act as receptors for toxins and drugs
  • have a role in cell adhesion in some tissues
42
Q

glycolipids

A

role in cell recognition, acting as cell markers or antigens

43
Q

cholesterol

A

may be present; restrict movement of other membrane components, making membranes less fluid, providing mechanical stability.

44
Q

immunity

A

ability of an organism to resist infection from invading disease-causing micro-organisms (pathogens)

45
Q

there are 2 types of lymphocytes

A
  • t lymphocyte cells (T cells) -> mature in thymus gland and are associated with cell mediated immunity
  • b lymphocyte cells (B cells) -> mature in bone marrow and are associated with humeral immunity
46
Q

antigens

A

specific molecules on a cell surface that identify it. usually molecules that include proteins found on the cell surface membrane or cell wall.
- the immune system can recognise cells as self or foreign.

47
Q

the immune system can identify antigens belonging to:

A

pathogens, cells from other organisms, abnormals body cells, toxins.

48
Q

phagocytosis

A

non-specific response to an invading pathogen that has entered the body. Phagocytes, a type of white blood cell engulf and destroy pathogens.

49
Q

cellular immune espone.

A
  1. pathogens invade body and are engulfed by phagocytes
  2. phagocyte comes antigen presenting cell
  3. APC presents antigens to Th cells
  4. antigen binds to comp Th cell receptor
  5. Th cell activated and stimulates other T cells causing rapid division and: stimulates phagocytes to engulf more pathogens, stimulates B cells and may activate cytotoxic T cells which kill infected cells by making holes in cell surface membranes.
50
Q

humoral immune response

A
  1. surface antigens of pathogen in blood are taken up by b cells
  2. B cells process and present the antigens on surface
  3. T helper bind to processed antigens and activate B cells
  4. activated B cells divide by mitosis and differentiates into plasma and memory cells.
  5. plasma cells produce antibodies comp to antigens
  6. antibodies attach to antigens on pathogen, leads to agglutination and phagocytosis (primary immune response)
  7. remaining B cells develop into memory cells that stay in blood stream. When they come into contact with antigen again they divide rapidly to form B plasma cells and B memory cells (secondary immune response).
51
Q

antibodies

A

globular protein produced by plasma cell in response to presence of specific, comp antigen

52
Q

vaccination

A

introduction of a substance containing appropriate antigens into the body to stimulate active immunity against disease.

53
Q

monoclonal antibodies

A

antibody that has been isolated and cloned.

54
Q

monoclonal antibodies are used in science and medicine for:

A
  • delivering medication to specific cell types
  • medical diagnosis (pregnancy kits, HIV)
  • ELISA
55
Q

HIV

A

retrovirus. Contains reverse transcriptase, which is able to synthesis single-stranded DNA from RNA template.
- weakens immune system by infecting and destroying Th cells -> AIDS.

56
Q

HIV replication

A
  1. HIV attaches to CD4 surface receptors on Th lymphocyte and injects reverse transcriptase and RNA into cell
  2. Reverse transcriptase uses viral RNA as a template to make DNA copy which gets inserted into host chromosome
  3. viral DNA is transcribed to make viral mRNA and translated to make viral proteins
  4. viral proteins and RNA form new HIV particles, which burst out of host cell to infect more Th cells
  5. this destroys Th cells, leading to dramatic reduction in immune capability of host.

AQA Biology A-level (8 decks)

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