Topic 1: Cell Biology Flashcards Preview

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Flashcards in Topic 1: Cell Biology Deck (66):
1

Cells

The basic structural and functional units of almost all living things

2

Compartmentalisation of cells

Eukaryotic cells have membrane-bound organelles that can form compartment-like structures
These can make for different intracellular environments for different cellular activities so that each subcellular compartment carries out specific functions

3

Why are viruses sub cellular organisms and not considered as living?

They behave like chemicals and can be purified, even crystallised, because they are of uniform shape and size
Metabolically inert
Do not have organelles
Need living cells for propagation
Produce a range of viral proteins, using host ribosomes

4

The cellular environment/internal environment

The immediate surrounding of cells is the layer of fluid
AKA intercellular, interstitial, extracellular, tissue fluid
Must be kept constant if the cells are to continue their vital functions
If the conditions change beyond tolerance limit of cells, the cells will die

5

Apoptosis

Programmed cell death
Part of the normal developmental processes of cells but can also occur if cell has lost its normal controls and starts to proliferate in an unregulated manner
In fully formed tissue, cell death and cell reproductions are generally balanced

6

Necrosis

Cell death due to mechanical or chemical trauma to tissue or cell

7

Physiological apoptosis

Embryogenesis and fetal development
Formation of the fingers and toes of the foetus
Sloughing off of the inner lining of the uterus
Death of cells that have served their function (neutrophils, lymphocytes
Cells at the end of the cell cycle
Damaged or dysfunctional cells
Excessive cells

8

Pathological apoptosis

DNA damage due to radiation, chemotherapy
Cell death in viral infections that induce apoptosis (HIV and Adenovirus)
Organ atrophy after duct obstruction (polio)

9

Change in cells during Necrosis

1. Cellular swelling
2. Plasma membrane ruptures
3. ATP is depleted
4. Cellular and nuclear lysis causes inflammation
5. random DNA fragmentation
6. In vivo, whole areas of the tissue are affected

10

Change in cells during Apoptosis

1. Cellular condensation
2. DNA is cleaved into multiples of 200 base pair units
3. Formation of blebbing in the plasma membrane and structural proteins are cleaved, leading to nuclear breakdown. Membrane remains intact. Cellular organelles start to fragment
4. Cell fragments into apoptotic bodies
5. Dying cells secrete factors that recruit phagocytes
6. Apoptotic bodies are engulfed by phagocytes
7. Dead cells disappear and do not produce inflammation
Process requires ATP
In vivo, individual cells affected
No inflammatory reaction

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Mitochondrial pathway AKA

Intrinsic pathway

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Death receptor pathway AKA

Extrinsic pathway

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Mitochondrial pathway (Apoptosis)

1. DNA damage or malfunction of oxidative enzymes (enzymes associated with cell respiration) initiate reaction on the surface proteins of the mitochondria wall.
2. Damaged proteins on the mitochondria membrane punch holes in the outer mitochondrial membrane, causing Cytochrome C to leak out into cytosol
3. Using ATP, released cytochrome C binds to the specific protein
4. Cytochrome and other compounds in cytosol activate caspase 9 (initiator caspase)
5. Activated caspase 9 then activate caspace 3,6 and 7 (cleaving enzymes)
6. These activated caspase varieties then cleave DNA, proteins in nuclear envelope, cytoskeleton and golgi complex
7. Blebs will develop and apoptotic bodies appear
8. Phagocytes engulf these apoptotic bodies

14

Major contributions to Apoptosis via mitochondrial/intrinsic pathway

DNA damage
Damage to organelles
Collection of reactive oxygen species (ROS)

15

Death receptor pathway (Apoptosis)

1. External stimulus reaches the cell membrane and starts a cascade of reactions involving enzymes inside the cell
2. Receptors exposed at the surface of the cell bind to the complementary death activator and transmit a signal to the cytoplasm that leads to activation of caspase
3. Activated pro caspase 8 is converted to active caspase 8 (initiator)
4. Activated caspase 8 then activates caspase 3,6 and 7 (executioner caspases)
5. Activated caspases degrade and dismantle a variety of proteins in the cell
6. Apoptotic bodies are formed and these are engulfed by the phagocytic cells
7. Phagocytic cells secrete cytokines that inhibit inflammation

16

Telomeres

Cap the end of chromosomes and protect the chromosome
As cell divides, telomeres continuously shorten with each successive cell division
Shortening of telomeres results in cell death and apoptosis

17

Rheumatoid Arthritis

Excessive proliferation of cells (poor apoptosis) in the synovial tissue of the joints that leads to joint destruction

18

Cancer

An uncontrolled increase in cell numbers in tissues, leading to the formation of a tumour.
If the tumour continues to grow and invades healthy cells, it is malignant

19

Apoptosis defaults

Poor apoptosis may lead to cancer and too much apoptosis can lead to degenerative diseases like Alzheimers

20

Cancer cells

Caused by impaired signalling from death receptors located on the membrane of the cancer cells
Lose the molecules on their surface that keep normal cells in the right place, so they become detached from neighbouring cells
Dont mature or become specialised

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1mm

1000 um

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1 um

1000nm

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1nm

10Ao

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Order of units

mm-um-nm-Ao

25

Centrifugation

Process that separates solids from liquids and liquids of different densities from each other by using centrifugal force

26

Differential centrifugation

AKA fractionation
Separate undamaged intact cellular organelles
Sample must be kept cool to prevent self digestion

27

Density gradient centrifugation

Separates organelles into defined physical layers according to their specific density
Sucrose is added to sample before centrifugation
Dense molecules settle fastest, based on gravitational force. Smaller and less dense molecules stay suspended longer.

28

Order- density gradient centrifugation

Bottom to top
Cellular debris, nuclei, mitochondria or lysosome, ER, ribosomes

29

Homogenization

Process of rupturing a cell by centrifugation

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How does centrifugation work

By varying centrifugation force (speed) and time, while maintaining a continuous media density, different sizes of particles can be separated on the basis of their size.

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Prokaryotes

Bacteria (monera) and archaea, algae

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Eukaryotes

Animalia, Plantae, Protista, Fungi

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Differences between eukaryotes and prokaryotes

Eukaryotes- double linear chromosomes, nucleus, organelles
Pro- single circular chromosomes, no nucleus, no organelles

34

Organelles

Membrane-bound cellular structures that perform specific functions within a cell, embedded within the cell's cytoplasm

35

Plasma membrane

Outer cover of a cell
Boundary between inter cellular and extracellular environments
also covers several cellular organelles
7-9nm thick
organelle membrane 5-7 nm

36

Cholesterol- PM

Disturbs close packaging of phospholipids
Regulates membrane fluidity and membrane stability
Make it less soluble to very small water soluble molecules that could otherwise pass easily

37

Glycoproteins

Carbohydrate chain attached to protein
Cellular recognition, act as receptors for hormones and neurotransmitters.

38

Integral proteins

Completely penetrate the lipid layer
Control the entry and removal of specific molecules from the cell

39

Glycolipids

Carbohydrate chain attached to a lipid molecule
Surface receptors and stabilise the membrane

40

Peripheral protein

Loosely associated with the membrane surface

41

Plasma membrane flexibility

Phospholipid molecules are very flexible, allowing the cell to change shape, expand and contract
Allows the plasma membrane to break and reorganise again in cytokinesis

42

Fluid mosaic model

The phospholipid remain a thick fluid with proteins embedded and moving freely within it, giving it an appearance of a mosaic

43

temperature effect on Plasma membrane

More fluidic in colder temperatures as lipid molecules tend to cluster together but having cholesterol increases the movement of lipids

44

Glycocalyx

Carbohydrate chains attached to the outer surface of the membrane
Glycolipids and glycoproteins

45

Transport proteins

Allow charged substances to move through the membrane and substances that could not otherwise pass directly through the membrane

46

Receptor proteins

Bind with hormones and transmit the message to inside of the cell, causing change to cell activities.
Each receptor is specific for a specific signal molecule (ligand)

47

Recognition proteins

Attached to carbohydrate molecules
Act as markers (antigens) which cause immune system to distinguish between self and foreign cells
glycoproteins, MHC markers

48

Adhesion proteins

Cell adhesion molecules allow cells to interact and attach to a surface, substrate or another cell, mediated by interactions between molecules of the cell surface
Transmembrane glycoproteins

49

Cell membrane functions

Maintain integrity of cell by regulating passage of molecules into and out of cell
Receives information about changes to its surroundings and responds to these changes
Involved in cell-cell recognition- produce electrical charge in nerve cells for communication

50

Cytosol

Aqueous solution of molecules with a gel-like consistency
semi solid and composed of water, minerals, salts and different kinds of organic compounds

51

Protoplasm divisions

Protoplasm is everything within the plasma membrane
Divided into cytoplasm + nucleus
Cytoplasm is everything except nucleus
Divided into cytosol + organelles
Cytosol is the pure liquid component of cells ie no organelles or cytoskeleton

52

ER

network of membrane connected by tubular canals
Most of these canals start from the cell membrane and end in the outer layer of nuclear wall, arranged as flattened sacs.
Cisternal spaces of ER have such a high SA:V ratio that the ER constitutes over half of the total membrane in the cell.
ER also forms direct connections between adjacent cells as it passes through the plasmodesmata between cells

53

Rough ER

Isolate and transport proteins, which have been synthesised by ribosomes
Intra cellular transport
Synthesis glycoproteins in the cisternal spaces
Form a structural skeleton for maintaining cellular shape

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Smooth ER

Synthesis and transport of lipids and steroids
Manufacture of cholesterol and phospholipids
Detoxifying lipid soluble compounds
Some enzymes in the SER convert water insoluble compounds to water soluble compounds by adding OH group for removal from the body
Stores calcium

55

Golgi complex (not function)

Sacks of flattened cavities lined with smooth ER.
Nine layers in animal cells and over hundred in planet cells
Common in secretory cells like nerve cells and those that produce digestive enzymes

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Cisternal spaces

Spaces in Golgi complex and rough ER where proteins packaged

57

Vesicles surrounding golgi complex

Large and small vesicles containing secreting granules
Move to the surface of the cell where the secretion is released
Other vesicles may become lysosomes

58

Golgi complex function

Site of production of cellular secretions, lysosomes, cell membrane
Packaging and modifying proteins
Package materials into membrane bound vesicles to send out of the cell
Produce polysaccharides (required to make cell wall and assembles them inside plasma membrane to send outside through small pores in plasma membrane) and proteoglycans

59

Vesicle formation

The means by which materials are sorted and distributed throughout the cell

60

Mitochondria numbers

Number of mitochondria depends on energy needs of cell
More in active cells like amoeba and muscle fibres

61

Mitochondria (not function)

have own DNA, make own proteins and are able to grow and divide
seen using light microscope
has two membranes
inner membrane is highly folded giving rise to an irregular series of cristae which projects into the interior. Contains electron transport chains.
Inside mitochondria is the matrix with chemicals and enzymes (DNA, RNA, ribosome, amino acids all present)

62

Mitochondria functions

Produce energy (ATP) through series of reactions
Krebs cycles occurs in mitochondrial matrix

63

Lysosomes (not function)

Digestive organelles
only in animal cells
have about 7 digestive enzymes powerful enough to destroy entire cells
digestion is carried out in vacuoles covered by membrane. Lysosomes discharge their contents into these vacuoles.

64

Lysosomes functions

Destroy bacteria and other foreign organisms, worn out organelles
Replacement of tissues during growth
Involved in programmed cell death where lysosome membrane ruptures thereby freeing the enzymes, which can destroy an entire cell

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Ribosomes

Made up of a complex of rRNA and protein
No membrane cover
Ribosome subunits made in the nucleus
Protein synthesis

66

Polyribosome

When several ribosomes are attached to a mRNA strand