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B3 - Cell Structure Flashcards

1
Q

What were the 3 main ideas in cell theory?

A

All living organisms are made up of one or more cells
Cells are the basic functional unit in living organisms
New cells are produced from pre-existing cells

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2
Q

What is the role of the cell surface membrane?

A

Controls the exchange of materials between the internal cell environment & the external environment

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3
Q

What is the structure of the cell surface membrane?

A

It is partially permeable, and fluid - constantly in motion
Primarily made up of phospholipids and proteins

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4
Q

What is the role of the cell wall?

A

Provides structural support to a cell

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5
Q

What is the structure of a cell wall?

A

They are made up of polysaccharides - cellulose in plants, and peptidoglycan in most bacterial cells
Narrow threads of cytoplasm (surrounded by a cell membrane) called plasmodesmata connect the cytoplasm of neighbouring plant cell
Very strong & insoluble
Lignin and pectin further increases the strength & support to the plant

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6
Q

What does the nucleus contain that forms chromosomes?

A

Chromatin which binds
to histone proteins to form chromosomes

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7
Q

What is the nuclear evenlope?

A

A double membrane with pores (nuclear pores) which allow mRNA & ribosomes to leave the nucleus, and enzymes to enter

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8
Q

What is a nucleolus?

A

Site of ribosome production

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9
Q

What is the role of the mitochondria?

A

Site of aerobic respiration

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10
Q

What is the structure of mitochondria?

A

Surrounded by a double-membrane, with the inner membrane folding to form cristae
The cristase forms the matrix, where many enzymes needed for respiration can be found
Small, circular mitochondrial DNA (mtDNA) and ribosomes are also found here

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11
Q

What is the role of chloroplasts?

A

Site of photosynthesis

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12
Q

What is the structure of the chloroplast?

A

The light-dependent stage takes place in the thylakoids
The light-independent stage takes place in the stroma
Surrounded by a double-membrane
Thylakoids (containing chlorophyll) stack → form a granum (grana)
Grana join together to form a lamella (lamellae)
Also contain small, circular DNA and ribosomes are also found here

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13
Q

What is the role of a ribosome?

A

Site of protein synthesis

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14
Q

What is the structure of a ribosome?

A

Each ribosome is a complex of ribosomal RNA (rRNA) and proteins
80S (heavier than prokaryotes) ribosomes are found in eukaryotic cells
70S ribosomes in prokaryotes, mitochondria and chloroplasts

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15
Q

Where are ribosomes found?

A

Freely in the cytoplasm or in the rough endoplasmic reticulum

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16
Q

What is the structure of the rough endoplasmic reticulum (ReR)?

A

Surface covered in ribosomes
Formed from continuous folds of membrane that is attached to the nuclear envelope
Processes proteins made by the ribosomes

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17
Q

What is the structure of the smooth endoplasmic reticulum (SeR)?

A

Does not have ribosomes on the surface
Involved in the production, processing and storage of lipids, carbohydrates and steroids

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18
Q

What is the structure of the Glogi apparatus/complex?

A

Flattened sacs of membrane
Responsible for modifying proteins and lipids, pack them into golgi vesicles, vesicles transport proteins and lipids to their destination
Proteins that go through the Golgi apparatus are usually exported, put into lysosomes, or delivered to membrane-bound organelles

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19
Q

What is the structure of a large permanent vacuole?

A

Sacs in plant cells surrounded by the tonoplast (selectively permeable membrane)
Helps maintain turgor pressure in a plant cell
Stores water, salts, minerals, pigments & proteins within a cell

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20
Q

What is the structure of a vesicle?

A

Membrane-bound sacs for transport & storage

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21
Q

What is the structure of a lysosome?

A

Specialist forms of vesicles which contain hydrolytic enzymes (enzymes that break biological molecules down)
These enzymes break down waste materials such as worn-out organelles
Cells of the immune system & cells involved in apoptosis use lysosomes a lot

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22
Q

What are microvilli?

A

They are cell membrane projections that increase the surface area for absorption

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23
Q

What are cilia?

A

They are hair-like projections made from microtubules
Allows the movement of substances over the cell surface

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24
Q

What are microtubules?

A

Microtubules make up the cytoskeleton of a cell (essentially a road network within cells) They provide support and allow movement within the cell
Made of a protein dimer (alpha & beta tubulin), dimers join to form a protofilament, many protofilaments form a microtubule

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25
What is a flagella?
Long microtubules that contract to provide cell movement
26
What is the function of a nerve cell?
Conduction of nerve impulses
27
What is the structure of a nerve cell?
Cell body Extended cytoplasm Insulated axon
28
What are the adaptations of a nerve cell?
Cell body is where most of the proteins are synthesised Extended cytoplasm forms dendrites (receives signals) & axons (transmit signals) Neurons are able to communicate with each other, muscles and glands Axon is insulated with a fatty sheath, speeds up nerve impulse transmission
29
What is the function of a muscle cell?
Muscle contraction
30
What is the structure of a muscle cell?
Contain layers of protein filaments Many mitochondria
31
What are the adaptations of a muscle cell?
The protein filaments can slide over each other which causes muscle contraction Lots of mitochondria - provides energy for contraction
32
What is the function of a sperm cell?
Fertilisation
33
What is the structure of a sperm cell?
Nucleus in head Acrosome (containing digestive enzymes) Many mitochondria in midpiece Flagella
34
What are the adaptations of a sperm cell?
Head contains paternal DNA → fuses with maternal DNA within the egg Head also contains acroscome → breaks down the outer layer of the egg cell → nucleus can enter Lots of mitochondria - provides energy to propel the sperm Tail - rotates to propel the sperm forwards, towards the egg cell
35
What is the function of a root hair cell?
Absorb water & mineral ions from soil
36
What is the structure of a root hair cell?
Extended cytoplasm Thinner walls Permanent vacuole Lots of mitochondria No chloroplasts
37
What are the adaptations of a root hair cell?
Extended cytoplasm (root hair) increases the surface area → more water & ions absorbed Thinner walls - water can move through easily Permanent vacuole - contains cell sap & regulates the water potential gradient Mitochondria - for active transport of mineral ions
38
What is the function of a xylem cell?
Transport tissue for water and dissolved ions
39
What is the structure of a xylem cell?
Cells are dead (no cytoplasm & other organelles) No top & bottom walls Thickened outer walls (lignin)
40
What are the adaptations of a xylem cell?
No top or bottom walls - forms a hollow, continuous tube Cells are dead & empty - allows free passage of water Lignin - strengthens the tube & supports the stems of the plant
41
What is the function of a phloem cell?
Transport tissue for dissolved sugars & amino acids
42
What is the structure of a phloem cell?
Cells are alive Companion cells Cells contain holes in their end cell walls (sieve plates) Very few organelles within the vessel
43
What are the adaptations of a phloem cell?
Cells are mostly living & are supported by companion cells (provide energy to the vessel) Sieve plates act like a ‘sieve’, allowing sugars & amino acids to flow easily through Little amount of organelles - aids flow of materials
44
What do multicellular organism cells do?
They become specialised for specific functions. A group of cells work together to perform a particular function, this is a tissue. Different tissues work together to form organs. Different organs work together to form organ systems. E.g. muscle cell to muscle to heart to circulatory system
45
What is the difference in size between prokaryotic cells and eukaryotic cells?
Prokaryotic cells are between 100 to 1000 times smaller than eukaryotes. 0.5-5 micrometres comparted to up to 100 micrometres.
46
What is the difference in how DNA is organised between prokaryotic and eukaryotic cells?
In prokaryotes - Circular DNA found in the cytoplasm Eukaryotes - DNA found in the nucleus of the cell
47
How is cell division different between prokaryotic cells and eukaryotic cells?
Prokaryotes - Binary fission Eukaryotes - Mitosis
48
What is the difference in ribosomes between prokaryotic and eukaryotic cells?
Prokaryotes - Smaller (70S) Eukaryotes - Bigger (80S)
49
What is the difference in sub-cellular organelles between prokaryotic cells and eukaryotic cells?
Prokaryotes - plasmids (small loops of DNA), capsules (final outer layer), flagellum (allows movement) and pili (attachment to other surfaces) Not found in all prokaryotes Eukaryotes - Mitochondria, rough and smooth endoplasmic reticulum, chloroplast ...
50
What is the difference in cell walls between prokaryotic and eukaryotic cells?
Prokaryotes - Made of peptidoglycan and murein Eukaryotes - Cellulose in plants and Chitin in fungi
51
What are the features of virus particles?
Viruses are non-cellular infectious particles Simple & smaller than prokaryotic cells (20 - 300 nm) They are parasitic so can only reproduce by infecting living cells and use their machinery (ribosomes) to make copies of themselves Acellular (not made up of cells) so can't undergo cell division
52
What is the structure of virus particles?
Nucleic acid core (either a DNA or RNA genome and can be single and double-stranded) A protein coat - a capsid Some have phospholipid-based outer layers
53
How do Viral cells work (HIV as example)?
They require host cells in order to reproduce: Viral attachment proteins, help viruses bind to host cells Viral RNA is injected into the host cells Reverse transcriptase converts ssRNA into dsDNA The dsDNA is inserted into the host cell's’ genome, and is used to produce new viral particles ss=single stranded ds=double stranded
54
Why are microscopes used?
Analyse cell components and observe organelles
55
What is magnification?
How many times bigger the image produced by the microscope is, compared to the real object under the microscope
56
What is resolution?
The ability to distinguish between objects that are close together
57
What are the 2 types of microscope?
Optical/Light Electron (both TEMs and SEMs)
58
How do optical microscopes work and how good are they?
Use light to form an image Resolution is limited 200nm Can only observe eukaryotic cells, nuclei, mitochondria and chloroplasts Max magnification of x1,500
59
How do electron microscopes work and how good are they?
Use electrons to form an image Increased resolution, electron beams have a smaller wavelength than light, so can resolve objects close together Max. resolution of 0.2nm Can be used to observe small organelles, ribosomes, endoplasmic reticulum or lysosomes Max magnification is x1,500,000
60
How do Transmission electron microscopes (TEMs) work and what are their pros and cons?
TEMs use electromagnets to focus a beam of electrons, the beam is transmitted through the specimen The denser parts of the specimen absorb more electrons so appear darker + Give high-resolution images + Allows the internal structures within cells + within organelles to be seen - Only be used with very thin specimens / thin sections - Can’t be used to observe live specimens - Specimens take time to prepare so increases the likelihood of artefacts being introduced - Do not produce a coloured image
61
How do Scanning electron microscopes (SEMs) work and what are their pros and cons?
SEMs scan a beam of electrons across the specimen, the beam bounces off the surface of the specimen, then electrons are detected which forms an image +Produce 3D images that show the surface of specimens + Can be used on thick or 3D specimens -Give a lower resolution image than TEMs - Can’t be used to observe live specimens - Do not produce a coloured image
62
What is a graticule?
A small disc that has divisions, but no scale. Can be placed into the eyepiece of a microscope to act as a ruler in the field of view
63
What is a stage micrometre?
Microscope slide with divisions 0.1mm apart
64
How do you work out 1 graticule division (magnification factor) ?
Number of micrometres / number of graticule divisions
65
How do you find the total magnification?
eyepiece lens magnification x objective lens magnification
66
How is image size calculated?
Actual size x magnification (I=AM)
67
What is cell fractionation?
The process of separating cell organelles from each other - often for imaging or research purposes
68
What are the 3 steps of cell fractionation?
Homogenisation Filtration Ultracentrifugation
69
What is the process of homogenisation?
Tissue sample placed in cold, isotonic buffer The sample + solution is then homogenised using a homogeniser - blender-like machine that grinds the cells up This break the plasma membrane → organelles are released - now called the homogenate (product)
70
What is the process of flitration?
The homogenate (product) is filtered through a gauze This separates larger cell debris that wasn’t broken down Smaller organelles are not filtered out The filtrate is left- a solution containing a mixture of organelles
71
What is the process of ultracentrifugation?
The filtrate (filtered product) is placed into a tube and the tube is placed in a centrifuge The filtrate is first spun at low speed → largest, heaviest organelles (e.g., nuclei) settle at the bottom of the tube → forms a pellet (thick, sediment-like material) + the supernatant (rest of the solution, containing organelles) The supernatant is then centrifuged again → process repeated at increasing speeds until all different types of organelles present are separated out OR the desired organelles is found
72
What are artefacts?
Things you may see in a prepared slide that aren’t part of the specimen, and often occur during the preparation of a sample
73
What happened during early research using microscopes?
Scientists using the microscopes found it difficult to distinguish between artefacts and organelles
74
What are the 3 phases of the cell cycle?
Interphase Mitosis Cytokinesis
75
Which part of the cell cycle takes the longest?
1. Interphase (Mainly G1) 2. Mitosis 3. Cytokinesis
76
What are the names of the 3 phases in the interphase?
G1 phase - Growth S phase - Synthesis of new DNA G2 phase - Further cell growth
77
What occurs in G1 (growth)?
Cells produce RNA, enzymes, and other proteins required for cell growth Cells receive a signal to divide - controlled by cyclins
78
What occurs in the S phase?
DNA in the nucleus replicates → each chromosome contains two identical sister chromatids
79
What occurs in the G2 phase?
Newly synthesised DNA is checked for any errors → (normally) repaired Tubulin is also made - protein needed for mitosis
80
What is mitosis needed for?
Growth of multicellular organisms Replacement of cells & repair of tissues Asexual reproduction - reproduction with a single parent organisms
81
What are the 4 stages of mitosis?
Prophase, Metaphase, Anaphase, Telophase (PMAT)
82
What are centrosomes?
Centrosomes are organelles that become visible during mitosis, helping to pair up & move chromosomes They contain two centrioles, where spindle fibres (protein microtubules) emerge and attach to centromeres in the middle of chromatids
83
What are centromeres?
Where copied chromosomes are joined together (like blue-tac)
84
What occurs during the prophase?
Chromosomes condense Copied chromosomes are joined together at the centromere Centrosomes move to opposite poles → spindle fibres emerge from them Nuclear envelope breaks down into vesicles
85
What occurs during the metaphase?
Sister chromatids line up at the equator of the spindle ( the middle of the nucleus) Spindle fibres attach to the centromeres
86
What occurs during the anaphase?
Sister chromatids separate at the centromere (which divides in two) Spindle fibres shorten & pull the separated sister chromatids (now called chromosomes) pulled to opposite poles
87
What occurs during the telophase?
Chromosomes arrived at opposite poles & decondense Nuclear envelope reforms around each set of chromosomes Spindle fibres break down
88
What is cytokinesis?
Cytokinesis is the physical separation of the parent cell into two genetically identical daughter cells
89
How does cytokinesis occur in an animal cell?
A ‘cleavage furrow’ (folded membrane) forms and separates the daughter cells
90
How does cytokinesis occur in a plant cell?
A ‘cell plate’ (the precursor to a new cell wall) forms at the site of the metaphase plate → new cell walls are produced → separates the new daughter cells
91
Why do cancers arise?
Due to uncontrolled mitosis → divide repeatedly and uncontrolled → forms a tumour (irregular mass of cells)
92
What is the name of mutated genes that cause cancer?
Oncogenes
93
What are benign tumours?
Tumours that do not spread from their original site & do not cause cancer
94
What are malignant tumours?
Tumours that spread through the body, invading & destroying other tissues & causes cancer
95
What are carcinogens?
agents that cause cancer (by mutations)
96
What is metastasizing?
When smaller tumours break off the tumour, they travel through the bloodstream, and may block the intestines, lungs or blood vessels
97
What is methotrexate?
A drug that inhibits the synthesis of DNA nucleotides in cells
98
What is Vincristine and taxol?
A drug that prevents the formation of spindle fibres

Biology (21 decks)

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