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Biochemistry > Cells: The fundamental units of life > Flashcards

Cells: The fundamental units of life Flashcards

1
Q

List the ways in which cells differ in order to fulfil their function.

A

Size, shape, chemical requirements (i.e what they need to survive).

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2
Q

State why cells in a multicellular organism can specialise to the point of being unable to sustain themselves while single-celled organisms can’t.

A

Other cells are required to perform the more basic functions of these hyper-specialised cells (i.e gametes transfer genetic info to the next generation because other body cells can’t). Unicellular organisms can’t do this.

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3
Q

State the 7 life-defining characteristics. Think “OR HADES”. You can remember this acronym by thinking it’s these life traits or Hades (death).

A

Living things:
O - Are more ORDERED than natural inanimate objects.
R - REPRODUCE.
H - Show HOMEOSTASIS (keep somewhat constant internal environment).
A - ADAPT to their environment.
D - DEVELOP from a basic starting point.
E - Absorb and transform ENERGY from their surroundings.
S - Respond to STIMULI.

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4
Q

All living organisms contain genetic info composed of DNA (in the form of genes). True or false?

A

True. Only viruses can have RNA as their genetic info.

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5
Q

What is transcription in simple terms?

A

Creation of RNA from its respective encoded DNA nucleotide sequence.

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6
Q

What is translation in simple terms?

A

Creation of a linear amino acid sequence from its corresponding RNA.

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7
Q

DNA comes in long polymer chains. What are its monomers?

A

Nucleotides: Adenine, Cytosine, Thymine and Guanine.

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8
Q

Name 2 polynucleotides.

A

DNA and RNA.

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9
Q

Define central dogma.

A

The flow of genetic info via transcription (from DNA to RNA) then translation (RNA to protein).

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10
Q

What mainly decides a cell’s appearance and behaviour?

A

Its protein molecules.

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11
Q

How many naturally ocurring amino acids are there?

A

20.

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12
Q

Define conformation in terms of proteins.

A

The 3D shape of a protein that depends on the sequence of its amino acids.

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13
Q

Describe the two mechanisms that allows cells to self-replicate. Note - they’re feedback loops between proteins and polynucleotides.

A

“Life is an autocatalytic process.”

  1. DNA/RNA provide info for making proteins and copying themselves.
  2. Proteins provide catalytic activity to make DNA/RNA/themselves.

Proteins and DNA synthesis/copying are required for self-replication.

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14
Q

What is the main reason viruses are considered non-living?

A

They can’t reproduce by themselves - they hijack the reproductive machinery of the host cell to replicate. They do still contain DNA/RNA though.

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15
Q

What makes a mutation good/bad/neutral?

A

The impact it has on the cell’s ability to survive and reproduce.

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16
Q

What is a mutation?

A

A mistake in the copying of DNA that changes its nucleotide sequence.

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17
Q

Why is it likely that all living cells evolved from the same ancestral cell?

A

All cells are different in shape, size and function but share the same fundamental chemical processes.

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18
Q

Define genome.

A

The full nucleotide sequence of an organism’s DNA.

Note: Genomes direct growth/development of plant/animal embryos and differentiation into a wide variety of cells.

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19
Q

Why are all cell types of an organism different but still share the same genome?

A

Different stem cells express different genes which causes them to take on the function and structure of a particular cell type (they make some RNAs/proteins but not others).

Note: the cell’s environment , internal state and cues from other cells will determine what it differentiates into.

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20
Q

When was the first microscope invented?

A

1665 by Robert Hooke. It was an optical/light microscope (using light as illumination source).

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21
Q

When was the electron microscope invented?

A

1930’s. It uses electrons as the illumation source, giving a higher resolution due to the shorter wavelength.

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22
Q

What did Robert Hooke notice when he observed cork under a microscope?

A

A mass of “cells” which were actually the remaining cell walls of the dead plant cells.

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23
Q

Name the two scientists who published papers (in 1938 and 1939) showing cells were the building blocks of living tissue (and started cell biology as a distinct science).

A

Theodore Schwann and Matthias Schleiden.

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24
Q

What is cell theory?

A

The principle that all living cells are formed by the growth and development of existing cells.

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25
Q

How did Louis Pasteur prove (1859) that living organisms can’t spontaneously occur but instead must be created from existing organisms?

A

He boiled a broth in a goose necked flask (allows air to flow through without risk of contamination). When the flask was left to sit, nothing happened. When the neck of the flask was removed, the broth became cloudy. When the flask was tilted and let sit, the broth also became cloudy. The broth only clouded when bacteria from outside the flask could get in - no life was spontaneously generated within the flask.

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26
Q

What is an extracellular matrix?

A

Protein fibres embedded in a gel of long sugar chains that separates cells in some tissues.

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27
Q

Why do we stain cells before observing them?

A

Subcellular structures are already small, but they’re also often transparent and colourless. Staining them makes them easier to see. Different dyes will stain different structures.

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28
Q

Other than staining a cell, how can you make organelles more distinct under a microscope?

A

Each organelle has a different refractive index (velocity at which light travels through it) so light is deflected upon travelling from one organelle to another. These differences in refractive index can be made visible and then enhanced by optical techniques and electronic processing.

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29
Q

What is the resolution of an optical microscope?

A

0.2um (points closer together than 0.2um can’t be distinguished from each other).

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30
Q

What is a plasma membrane?

A

The cell’s surface enclosing membrane.

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31
Q

What are fluorescence microscopes? What are their resolution?

A

New light microscopes which use illumination and electronic image processing to better observe stained cells and their organelles.
Their resolution is often 20nm.

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32
Q

What is the resolution of an electron microscope?

A

A few nanometers.

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33
Q

Outline how a tissue is prepared to be observed under a light microscope.

A

It’s fixed (pickled in a reactive chemical solution), embedded (in solid wax/resin), sectioned (cut into thin slices) then stained.

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34
Q

How are tissues prepared for electron microscopes?

A

The sections must be much thinner, stained with electron-dense heavy metals and living cells can’t be observed (they’re typically dried out first).

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35
Q

How thick are the membranes of most organelles? What are these membranes known as?

A

5nm.

Internal membranes.

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36
Q

Electron microscopes can resolve inividual large molecules, true or false?

A

True. Examples include DNA and large proteins.

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37
Q

How do transmission electron microscopes (TEMs) work?

A

Thin sections of the specimen must be used. An electron beam is fired through the sample.

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38
Q

How do scanning electron microscopes (SEMs) work?

A

They scatter electrons off the surface of samples to observe the surface detail of cells/organelles.

39
Q

Even powerful electron microscopes can’t see individual atoms within molecules. Name 2 methods that do allow this.

A

X-ray crystallography and cryoelectron microscopy.

40
Q

What do all organs/organelles have?

A

A membrane that makes it self-enclosed.

41
Q

Name the one organelle that bacteria have.

A

Ribosomes. They don’t even have a nucleus on account of being prokaryotic.

42
Q

What makes a cell eukaryotic or prokaryotic?

A

The presence/absence of a nucleus - eukaryotes have a nucleus (enclosed by a nuclear envelope), prokaryotes do not. Eukaryotic cells also have more organelles, most of which are membrane-bound.

43
Q

Explain, using a diagram, how light microscopes work in detail.

A

See page 12, first box of text book.

44
Q

Explain, using a diagram, how fluorescence microscopes work in detail.

A

See page 12, second box of textbook.

45
Q

Name two systems that exploit the difference in refractive index between organelles.

A

Phase-contrast optics and interference-contrast optics (these and standard optics can all be achieved by optical microscopes but require different components).

46
Q

Why are specimens cut into thin sections before being observed under a microscope?

A

To allow light/electrons to pass through so they can be properly observed under a microscope.

47
Q

Why are specimens chemically fixed before being observed under a microscope?

A

To preserve them in a life-like state.

48
Q

How do fluorescent molecules fluoresce?

A

They absorb light of one wavelength and emit light at another, longer wavelength.

49
Q

How can we stain specific organelles in a cell with dyes while not staining other parts?

A

Dyes used for staining will only bind specifically to certain molecules. I.e. one stain would be used for DNA while another would be used for a certain protein.
Other dyes can be attached to antibody molecules - the antibody binds to the molecule we want to identify, then the dye fluoresces under the microscope.

50
Q

How do fluorescent dyes allow objects smaller than 0.2um to be seen under a fluorescence microscope?

A

The dyes emit light themselves.

51
Q

Describe confocal fluorescence microscopy.

A

The confocal fluorescence microscope focuses a laser beam on a specific point within the specimen. A pinhole aperture in the microscope’s detector only allows fluorescence from that point to be included in the image. The beam is scanned across a thin section of the specimen to generate an optical section (image of section). Optical sections taken at different depths can be combined into a 3D image.

52
Q

Describe super-resolution fluorescence microscopy.

A

A technique that breaks the fluorescence microscope’s resolution limit of 200nm. The sample has molecules attached whose fluorescence can be switched on and off reversibly. Two lasers scan the sample: the central laser excites fluorescence in a small spot while the second (wrapped around the central laser) turns off fluorescence in the surrounding area.
Another approach is to map individual fluorescent molecules while turning off nearby molecules.
The resolution can be up to 20nm using these two approaches.

There is potential for this technique in 3D imaging and real-time live cell imaging.

53
Q

Draw a labelled diagram of a TEM.

A

See page 13, second box.

54
Q

Draw a labelled diagram of a SEM.

A

See page 13, third box.

55
Q

Describe how a TEM works.

A

Similar to a light microscope but an electron beam is used (shorter wavelength, higher resolution up to 1nm). Due to the short wavelength the specimen must be very thin. MAgnetic coils focus the beam instead of glass lenses.
Contrast can be introduced by staining sample with electron-dense heavy metals.
Specimen must be in a vacuum.

56
Q

Describe how a SEM works.

A

Specimen is coated in thin heavy metal film. Magnetic coils act as lenses and focus electron beam on specimen. A detector measures number of electrons scattered/emitted when beam bombards specimen’s surface. These measurements control the intensity of each point on the resulting image (on a video screen). The result is 3D images with resolution between 3 and 20nm.

57
Q

Describe the common shapes of bacteria and their typical size.

A

Bacteria are often a few micrometers long and are usually spherical, rod-shaped or spiral.

58
Q

State the two domains of prokaryotes.

A

Archaea and bacteria (while very similar, they’re only distantly related).

59
Q

Describe the typical structure of a prokaryote.

A

A single cell with a tough protective coat/cell wall surrounding the plasma membrane. The membrane encloses the cytoplasm and DNA. Electron micrographs show no obvious internal organisation.
Note: some prokaryotes cluster together into multicellular structures.

60
Q

Why are prokaryotes able to evolve so quickly? They can rapidly adapt to a new food source or resist being killed by a new antibiotic.

A

They already exist in large numbers and proliferate (reproduce) quickly. The can swap pieces of genetic material by a process similar to sex too.

61
Q

Why are prokaryotes considered such a chemically diverse class of cells?

A

They have a huge range of habitats, outnumber all eukaryotic organisms on Earth and can be either aerobic (use oxygen to oxidise food) or anaerobic (oxygen exposure kills them). Almost anything organic can be food to at least one type of bacterium.

62
Q

What is the suspected evolutionary origin of mitochondria?

A

They evolved from archaea-derived aerobic bacteria that were engulfed by (and lived inside) the anaerobic ancestors of modern eukaryotic cells. The membrane derived from the host’s membrane was lost (the two membranes the mitochondrion has were from the two membranes of the aerobic bacteria). It was a sort of symbiotic relationship - the host eukaryote and engulfed bacteria helped each other survive.

63
Q

What is the difference between cytosol and cytoplasm?

A

Cytosol is the concentrated intracellular aqueous gel, not including the organelles (often a cell’s largest compartment). Cytoplasm is everything contained within the plasma membrane (cytosol and organelles and their contents) except for the nucleus and its contents.

64
Q

How do some prokaryotes live entirely off inorganic substances? How do they get their carbon, nitrogen, oxygen, hydrogen and sulfur?

A 
Carbon: atmospheric CO2
Nitrogen: atmospheric N2
Oxygen: air
Hydrogen: water
Sulfur: inorganic minerals
65
Q

State two ways other than respiration that prokaryotes produce energy.

A
  1. Photosynthesis

2. Using chemical reactivity of inorganic substances in the environment.

66
Q

How do bacteria aid plants?

A

They help fix atmospheric nitrogen (plants can’t do this alone).

67
Q

What is the suspected evolutionary origin of chloroplasts?

A

They evolved from photosynthetic bacteria that lived inside the ancestors of modern aerobic eukaryotic cells (that already contained mitochondria).

68
Q

When did archaea and bacteria diverge from their common ancestor?

A

Around 3.5 billion years ago.

69
Q

How do the habitats of archaea differ from those of bacteria?

A

Archaea are extremophiles (they live in environments similar to the harsh conditions of primitive Earth) while bacteria live in more oxygen-rich environments.

70
Q

Name two types of single-celled eukaryotic organisms.

A

Yeast and amoeba.

71
Q

What encloses the nucleus of a eukaryotic cell?

A

The nuclear envelope (two concentric membranes).

72
Q

When are chromosomes visible in a nucleus?

A

When the DNA has been condensed to prepare for the cell to divide into two daughter cells.

73
Q

What do mitochondria look like under a fluorescence microscope?

A

Branching networks of worm-like structures.

74
Q

What do mitochondria look like under an electron microscope?

A

They are individually visible with one outer membrane and an inner membrane (which forms folds that project into the matrix).

75
Q

What is the basic chemical fuel for a cell’s functions?

A

ATP (Adenosine triphosphate).

76
Q

Observing a mitochondrion under a microscope won’t tell you its function. How was the function of mitochondria discovered?

A

By homogenising cells, centrifuging them (to separate cells by size and density) then chemically testing purified mitochondria.

77
Q

What is cellular respiration?

A

The process by which a mitochondrion absorbs oxygen and expells carbon dioxide, while creating ATP for the cell.

78
Q

Give two ways in which mitochondria resemble bacteria other than shape.

A
  1. They contain DNA.

2. They reproduce by dividing.

79
Q

The inner membranes of mitochondria contain most of the proteins needed for ATP production. Why is the inner membrane heavily folded?

A

To increase surface area for the reaction of making ATP.

80
Q

What types of cells house chloroplasts?

A

Plant and algal cells.

81
Q

Do mitochondria and chloroplasts have their own DNA?

A

Yes.

82
Q

What is the endoplasmic reticulum (ER)?

A

A membrane-enclosed maze of interconnected spaces. Most cell-membrane components and materials to be exported from the cell are made here.

83
Q

What is special about the ER in cells specialised for protein secretion?

A

It’s very enlarged.

84
Q

What is the golgi apparatus?

A

A stack of flat, membrane-enclosed sacs which modifies/packages molecules (made in the ER). The resulting products are sent to another cell compartment or secreted from the cell.

85
Q

What are lysosomes?

A

Membrane-enclosed organelles that perform intracellular digestion. They release nutrients from ingested food into the cytosol and break down unwanted molecules either for recycling or secretion. Small, irregular shape.

86
Q

What are peroxisomes?

A

Small, membrane enclosed vesicles that act as an isolated environment for inactivating toxic molecules using hydrogen peroxide.

87
Q

What are transport vesicles?

A

Small, membrane-bound vesicles that transport materials between membrane-bound organelles (typically the ER, golgi apparatus, plasma membrane and outside of the cell). They pinch off from one organelle’s membrane and fuse with another.

88
Q

What is endocytosis?

A

The process of a cell engulfing molecules or other cells by tucking the plasma membrane inward and pinching off a vesicle containing the engulfed material (now located within the cell). Animal cells can engulf larger things.

89
Q

What is exocytosis?

A

The process where vesicles in a cell fuse with the plasma membrane and release their contents into the cell’s surroundings (external medium). Hormones/other signal molecules are secreted this way.

90
Q

What is the main purpose of the cytosol?

A

To be the site of most chemical reactions in the cell.

91
Q

Do prokaryotes have vesicles?

A

No, as vesicles are membrane-bound organelles (they can’t engulf food particles and must share with others in the area).

92
Q

What is the cytoskeleton of a cell?

A

A network of protein filaments (anchored at one end to the plasma membrane of radiating out from a spot next to the nucleus). There are 3 types: actin filaments, intermediate filaments and microtubules.

93
Q

Where are actin filaments found?

A

In all eukaryotic cells, but in even higher concentrations in muscle cells (they’re important for muscle contraction).

94
Q

What is the purpose of microtubules (the thickest type of filament)?

A

In dividing cells they organise themselves into an array that helps pull duplicated chromosomes to opposite poles of the dividing cell (each daughter cell has an equal number of chromosomes).

Biochemistry (1 decks)

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