mod 1.1 - cell structure Flashcards
1
Q
What are the 3 points of cell theory?
A
1) The cell is the unit of structure for all living things
2) The cell exists as a distinct entity and as a building block for the construction of organisms.
3) All cells come from preexisting cells (cell replication)
2
Q
What was the first proto-life forms of cells?
A
Forms of cells would’ve been replicating molecules of genetic information (DNA & RNA).
3
Q
How did proto-life evolve into prokaryotic cells?
A
It settled itself in an oily lipid (fatty acid) bubble to protect it; this was known as the first cellular membrane, which formed the first prokaryotic cells.
4
Q
Why were prokaryotes successful?
A
Their free floating genetic material allowed for easy asexual binary fission.
5
Q
What is binary fission?
A
Asexual reproduction by a separation of the body into two new bodies.
6
Q
How did prokaryotes evolve into eukaryotes?
A
Formation of nuclear membrane around the genetic material to protect it and the formation of ER, which formed the first eukaryotic cells.
7
Q
What is the evolution of mitochondria and chloroplasts?
A
They weren’t developed by the cell itself, but instead hijacked bacteria led to an eventual mutual relationship → as bacteria would benefit from the protection of the large cell and the cell benefits from the products of the bacteria (eg: energy, glucose, production).
8
Q
What are the 4 common cell structures?
A
Cell membrane
Cytoplasm
DNA
Ribosomes
9
Q
What does the cytoplasm consist of?
A
It consists of the cytosol (gel-like substance composed of mainly water but also ions salts and organic molecules), and in eukaryotes, the organelles.
10
Q
What is DNA’s function in general?
A
Carries hereditary information that directs cell’s activity and is passed onto offspring.
11
Q
What are ribosomes in general?
A
Organelles responsible for the synthesis of proteins.
12
Q
What are proteins and polypeptides made of?
A
Proteins are large molecules composed of one or more polypeptides → Polypeptides are long, chain-like molecules consisting of many amino acids linked together.
13
Q
What are prokaryotes? give eg
A
Composed of prokaryotic cells, are usually unicellular and are smaller and less complex than eukaryotic cells. The organelles of prokaryotic cells are not membrane-bound. (eg: bacteria, archaea)
14
Q
What are eukaryotes? give eg
A
Composed of eukaryotic cells, contain membrane-bound organelles. (eg: fungi, protists, plants and animals)
15
Q
What are the 4 main groups of eukaryotic domain?
A
Plants
Fungus
Animals
Protists (type of pathogen)
16
Q
What are the 2 domains of prokaryotes:
A
Bacteria and Archaea.
17
Q
What is the domain of eukaryotes?
A
Eukarya.
18
Q
What are the 4 main kingdoms of eukaryotic domain?
A
Protista
Plantae
Fungi
Animalia
19
Q
Are prokaryotes unicellular?
A
Yes.
20
Q
Where are ribosomes found in prokaryotes?
A
The cytoplasm.
21
Q
Why are prokaryotes able to take in and release materials efficiently and replicate quickly?
A
Their small size allows for a large surface area relative to their volume (SA:V).
22
Q
Describe the genetic material of prokaryotes.
A
Single, circular DNA chromosome called the genophore which is located in an irregularly shaped region called the nucleoid. Many prokaryotic cells also contain small rings of double-stranded DNA called plasmids.
23
Q
Does the nucleoid have a nuclear membrane? (prokaryotes)
A
No.
24
Q
What is the genophore?
A
Single, circular DNA chromosome found in prokaryotes.
25
What are plasmids?
Small rings of double-stranded DNA in prokaryotes.
26
In prokaryotes, what is the cell membrane surrounded by?
A cell wall.
27
How does the chromosomal DNA anchor itself in prokaryotes?
It's attached to the cell membrane by a region of the chromosome called the origin.
28
Why do some bacteria have a capsule outside their cell wall?
Protects it from damage, dehydration, engulfment by eukaryotic cells, helps it to stick to surfaces and increase the virulence (ability to cause disease) of pathogenic bacteria.
29
What is virulence?
Ability to cause disease.
30
What is a flagellum?
A tail-like structure in prokaryotes that allow movement.
31
What are pili?
Small hair-like projections that allow motility and transfer of DNA between organisms in prokaryotes.
32
What are fimbriae?
Specialised pili that can attach to surfaces in prokaryotes.
33
Why are bacteria he most numerous type of organism in the biosphere?
They have extremely diverse metabolic systems, making them adaptable.
34
How do bacteria obtain energy?
From sunlight (photosynthesis) or by producing inorganic compounds such as sulfides or ferrous ions (chemosynthesis).
35
What are bacteria cell walls made of?
A polymer called peptidoglycan (also known as murein).
36
What is gram straining?
Adding purple dye called crystal violet to bacterial cells.
37
What are gram-positive bacteria? give eg
They have a thicker layer of peptidoglycan, therefore when interacting with the dye, they give a purple or positive result.
(eg: staphylococcus, streptococcus)
38
What are gram-negative bacteria? give eg
They have a thinner layer of peptidoglycan, therefore they don’t absorb the dye. (eg: cyanobacteria)
39
What are cyanobacteria
Blue-green photosynthesising bacteria that form dense colonies in shallow estuaries or freshwater.
40
What are archaea?
The prokaryotes in the domain Archaea include extremophiles, which are organisms that can live in extreme conditions.
(eg: high → thermophiles/low temperatures, upper atmosphere, alkaline/acidic environments, low oxygen/light areas, petroleum deposits underground)
41
How can archaea live in extreme environments?
Their cell membrane contains lipids that allow them to form a unique structure that remains fluid and selectively permeable (semipermeable) over a wide range of conditions.
42
Give examples of archaea.
```
Pyrococcus furiosus (underlined sus for comedic effect): a hyperthophile that survives in very hot temperatures such as undersea vents and withstand high pressures.
Sulfolobus: a thermophile also an acidophile that can survive in both high temperatures and high acidity.
```
43
What are the 3 differences between bacteria and archaea?
Archaea have a different type of lipid structure in the cell membrane.
The cell wall in bacteria contains peptidoglycan, but the cell wall in archaea does not.
Both have diverse metabolic systems, but methanogenesis (in which methane is produced) is unique to archaea.
44
What characteristics are unique to eukaryotes?
Multicellularity and sexual reproduction.
45
What are organelles?
Membrane-bound specialised structures in eukaryotic cells.
46
Differences between animal and plant cells.
Plant cells have cell walls made of cellulose outside of the cell membrane, which provides structural support. Animal cells don’t have cell walls.
Plant cells have a large, permanent vacuole, animal cells have many small, temporary fluid-filled vacuoles, known as vesicles, and don’t provide structural support.
Plant cells have chloroplasts, animal cells do not.
47
Why does diffusion occur more slower in eukaryotes than prokaryotes?
Smaller SA:V ratio.
48
Describe chromosomal DNA in eukaryotes.
Linear chromosomes which are located in the nucleus, separated from the cytoplasm by a double-layered membrane.
49
Where are ribosomes in eukaryotes?
Either attached to endoplasmic reticulum or free in cytoplasm.
50
Every prokaryote except what have a phospholipid bilayer?
Phospholipids in archaea are sometimes monolayer.
51
Cell membranes in eukaryotes are...
Phospholipid bilayer.
52
What are archaea cell walls made of?
Surface-layer proteins → rigid layer.
53
What are cell walls of protists made of? (keep in mind not all protists have a cell wall)
Carbohydrates.
54
What are cell walls of fungi made of?
Chitin.
55
What are cell walls of plants made of?
Cellulose.
56
Can eukaryotes have flagella or cilia?
Yes, some do.
57
What is cilia?
Fine hair like projections.
58
What is cell compartmentalisation?
The internal membranes (organelles) that form specialised membrane-bound compartments within the cell.
59
What is the role of organelle membranes?
The membranes control the movement of substances between the organelle and the cell’s cytosol (the liquid part of the cytoplasm) and enable each organelle to have a different composition from the surrounding cytosol and other organelles.
60
What are the benefits of cell compartmentalisation?
Allow enzymes and reactants for a particular cellular function to be close together in high concentrations and at the right conditions, so that processes in organelle are efficient.
Allowing processes that require different environments to occur at the same time, in the same cell, but in different organelles.
Making the cell less vulnerable to changes in the external environment.
61
What is mRNA?
| messenger RNA
DNA is transcribed inside the nucleus into mRNA.
mRNA moves out of the nucleus through nuclear pores and binds to ribosomes.
Ribosomes then synthesise proteins using the information on the mRNA.
62
What is structure of the nucleus?
Large organelle surrounded by a double membrane (is membrane bound). This membrane contains pores that link it with the cytosol.
63
What is the nucleolus?
The most visible structure on the nucleus is the nucleolus, which is composed of proteins, DNA and RNA, and is also where ribosomes are assembled.
64
What are ribosomes?
Ribosomes are composed of proteins and ribosomal RNA (rRNA) and are the sites of protein synthesis. Ribosomes translate the sequence of amino acids specified by the mRNA into proteins.
65
How big are ribosomes?
Only about 30 nm (nanometres) in diameter; therefore can only be seen under an electron microscope.
66
What is the structure of ribosomes?
Consist of two subunits joined together.
67
Where are ribosomes found and their roles in that area?
Proteins produced in free ribosomes will function in the cell’s cytosol, while proteins synthesised by ribosomes bound to the ER are secreted out of the cell, packaged into organelles or inserted into cell membranes.
68
What is the endoplasmic reticulum?
The endoplasmic reticulum is a network of intracellular membranous sacs (cisternae) and tubules.
It links with the cell membrane and other membranous organelles, including the nucleus.
69
What is the rough endoplasmic reticulum?
Once ribosomes have translated mRNA into proteins, the proteins pass through the ER cavity, which contains enzymes.
The enzymes add sugar molecules to the proteins to form glycoproteins.
Rough ER is abundant in cells that actively produce and export proteins, such as pancreatic cells, which secrete digestive enzymes.
From the rough ER, proteins move to the Golgi apparatus for export from the cell.
70
What is the smooth endoplasmic reticulum?
Contains the enzymes involved in the synthesis of molecules other than proteins, such as phospholipids and steroids.
Abundant in steroid-secreting cells in the testes, ovaries, kidneys and adrenal glands.
71
What is the Golgi apparatus also known as?
Golgi body or Golgi complex.
72
What makes the cisternae in the Golgi body different to the ER?
The cisternae in the Golgi apparatus is not connected.
73
What is cisternae?
The flattened disks of the endoplasmic reticulum and the Golgi apparatus.
74
What is the function of the Golgi apparatus?
When proteins from the ER reach the Golgi body, vesicles are formed in each cisternae, and these vesicles transport the proteins from one cisternae to the other, where they are modified for use by the cell, or for transport out of the cell.
The cisternae then form transport vesicles to move the modified proteins into the cytosol, into other organelles, or out the cell.
- packaging and transportation of proteins.
75
Provide an example of the transportation of proteins from the Golgi apparatus.
Digestive enzymes sent to lysosomes are not released from the cell, while secreted hormones are exported from the cell.
76
What is the two faces of the Golgi apparatus?
Cis face and trans face.
77
What is the cis face?
The cisternae of the cis face are connected to the ER (either directly or by small transport vesicles).
The cis face allows proteins made in rough ER to move into the Golgi apparatus.
Membranes in the cis face resemble those in the ER.
78
What is the trans face?
The cisternae of the trans face are connected to the cell membrane through large secretory vesicles that contain proteins to be secreted out of the cell.
Membranes in the trans face resemble those in the cell membrane.
79
What are lysosomes?
Lysosomes are the cell’s recycling units, and are specialised vesicles that digest unwanted matter.
Lysosomes contain digestive enzymes that break down cellular waste and debris.
The matter that isn’t broken down is released from the cell through exocytosis.
80
How are lysosomes formed?
When enzymes from the Golgi apparatus fuse with a vesicle called endosome.
81
What is the the two membranes of a mitochondrion?
The inner membrane: which has folds called cristae.
| The outer membrane.
82
What is the the two compartments of a mitochondrion?
An intermembrane space.
| The matrix.
83
What is the matrix in the mitochondria?
A fluid-filled space enclosed by the inner membrane which contains a double-stranded DNA molecule
84
What is the mitochondria's function?
Mitochondria play an important role in cellular respiration, and convert the chemical energy in organic molecules (from food) into energy that cells can use.
85
How does the amount of mitochondria in a cell vary? give eg
The amount of mitochondria in a cell is related to the cell's energy requirements. (eg: heart muscle cells are very active and therefore have many mitochondria)
86
Where is the site of cellular respiration?
The inner mitochondrial membranes are the site of cellular respiration and the highly folded cristae increases the surface area over which these chemical reactions can take place.
87
What is the cristae?
Cristae are folds in the inner membrane that extend into the matrix, increasing the functional surface area of the inner membrane.
88
What are the three membranes of chloroplasts?
The outer membrane.
The inner membrane.
The thylakoid system: disc-shaped sacs that form compartments within the chloroplasts (these different compartments contain different enzymes).
89
What is the function of chloroplasts?
Chloroplasts trap light energy which split water molecules into hydrogen and oxygen.
[Hydrogen then combines with carbon dioxide to make glucose; and oxygen is released as a waste product]
90
What two organelles other than the nucleus contain a double-stranded DNA?
Chloroplast and mitochondria.
91
What is the green pigment in chloroplasts called?
Chlorophyll.
92
What is granum?
Stacks of thylakoid.
93
What is stroma?
Region outside the thylakoid membrane. (fluid in inner membrane)
94
What are centrioles?
Centrioles are a pair of small, cylindrical structures composed of microtubules.
They are involved in cell division and the formation of cell structures such as cilia and flagella.
95
What are cilium & flagellum?
Cilia and flagella (plural) are hair-like structures on the surface of cells.
They consist of an arrangement of microtubules that are enclosed by an extension of the cell membrane.
Both are involved in the movement of the cell or things around the cell.
96
What is a vacuole?
A liquid-filled space that stores enzymes and other organic and inorganic molecules.
97
What are plastids?
Organelles involved in the synthesis and storage of different chemical compounds.
They contain a double-stranded DNA molecule.
Plastids develop from simple organelles called proplastids.
They are not in animal cells.
98
What are the 3 types of plastids?
Chloroplasts: involved in photosynthesis and are found in plants and some protists.
Leucoplasts: involved in storage. (eg: leucoplasts found in plants synthesise and store starch, but also convert the starch back to sugar when needed)
Chromoplasts: which contain colour pigments and occur in petals and fruit.
99
What are cell walls?
A rigid structure that surrounds the cell membrane.
The cell wall provides support, prevents expansion of the cell and allows water and dissolved substances to pass freely through it.
100
What is a cytoskeleton?
Consists of microtubules of a protein called tubulin, and filaments of a protein called actin.
It supports the cell’s structure, allows for mobility and helps transport organelles and vesicles within the cell.
101
What are the functions of the cell membrane?
Cell membrane encloses the contents of a cell and are semi permeable.
It controls the movement of substances between the extracellular fluid and the intracellular (or cytosol) inside the cell.
The cell membrane maintains an environment within the cell which differs from outside (homeostasis).
Cell membrane is also involved in cell recognition and communication with other cells.
102
What is the extracellular fluid for unicellular organisms?
The extracellular fluid is the watery, external environment in which they live, and they are not that protected from it’s conditions.
103
Why are multicellular organisms more protected from their external environment?
In multicellular organisms the environment of the cells is the extracellular fluid that surrounds them.
Most multicellular organisms can regulate the conditions of their internal environment, which allows them to provide specialised conditions for specialised cells and tissues.
104
What is the Fluid Mosaic Model?
The fluid mosaic model (proposed by Johnathan Singer and Garth Nicholson in 1972) is a representation of current knowledge of the cellular membrane that may be updated.
Cell membranes consist of a phospholipid bilayer.
Other molecules, such as proteins, carbohydrates and cholesterol, are scattered throughout the bilayer.
105
What are phospholipids made of?
a hydrophilic (water-attracting) ‘head’ - made of a phosphate group and glycerol, and two hydrophobic (water-repelling) ‘tails’ - made of fatty acids.
106
How are phospholipids arranged?
The hydrophilic heads from the outside and inside lining of the cell, and the hydrophobic tails meet at the centre.
The bilayer arrangement shelters the hydrophobic tails of the phospholipids from water, while exposing the hydrophilic heads to water.
107
How does the phospholipid structure of the membrane affect permeability?
Makes them impermeable to water-soluble particles, ions and polar molecules. (they have to enter via protein channels)
108
What gives the cell membrane its fluidity?
The ability of the phospholipids and proteins to move gives the cell membrane its fluid nature.
109
Why is fluidity in the cell membrane important?
It affects the permeability of the membrane and the capacity for proteins to move within the membrane to particular areas to carry out their function.
110
What are the factors that affect the fluidity of the cell membrane?
Temperature
Cholesterol
Proteins
Carbohydrates
111
How does temperature affect the fluidity of the cell membrane?
As the temperature increases, the fluidity increases in the membrane, as phospholipids are able to move more freely.
As temperature decreases, cell membranes with a large proportion of saturated fatty acids may solidify, however, this will not occur in cell membranes with a large proportion of unsaturated fatty acids, as the fatty acids’ tails prevent phospholipids from becoming too closely packed.
112
How does cholesterol affect the fluidity of the cell membrane?
Cholesterol is a fatty molecule that is located between phospholipid molecules.
The cholesterol found in eukaryotic cell membranes gives stability to the membrane without affecting its fluidity. It also reduces the permeability of the cell membrane to small, water-soluble molecules.
It doesn't really affect fluidity.
113
How do proteins affect the fluidity of the cell membrane?
They can move, however this movement may be limited to particular regions of the cell membrane.
114
What are the three types of proteins in the phospholipid bilayer?
Integral proteins
Peripheral proteins
Transmembrane proteins
115
What are integral proteins?
Proteins that are a permanent part of the cell membrane.
116
What are peripheral proteins?
Proteins that bind to integral proteins, or penetrate into one surface of the cell membrane.
117
What are transmembrane proteins?
When integral proteins span both phospholipid layers, and are involved in several important cellular and intracellular activities.
118
What is the role of carbohydrates in the cell membrane?
Carbohydrates in cell membranes are usually linked to protruding proteins (forming glycoproteins) or to lipids (forming glycolipids) on the outer surface of the membrane.
They also play a role in recognition and adhesion between cells, and in the recognition of antibodies, hormones and viruses by cells.
119
What is exocytosis?
Active transport in a cell that expels substances from the cell. (eg: cell waste, distribution of important proteins)
120
What is endocytosis?
Movement of material into a cell by enclosing it in a cell membrane which then pinches off to form a vesicle within the cell.
121
How to calculate magnification:
Total magnification = ocular lens (eyepiece) magnification x objective lens magnification
122
μm?
micrometre.
123
nm?
nanometre.
124
How to calculate field of view:
Field of view (mm) = (diameter (mm) x objective magnification) / total magnification
125
How to calculate cell size:
Length of each cell (mm) = field of view (mm) / number of cells
126
What are light microscopes?
Light microscopes use light and a system of lenses to magnify the image.
127
What is the magnification of light microscopes?
Up to x1000.
128
What is resolution?
Resolution is the ability to distinguish two objects as distinct.
129
What is the resolution limit of a LM?
The LM has a resolution limit of 0.2μm.
130
What can be seen with an LM?
Most cells can be seen, as well as some organelles (nucleus, chloroplasts, mitochondria and plant vacuole).
131
Other techniques with LM?
Staining techniques can enhance the contrast of the cell, such as phase-contrast which was developed to obtain better quality images using LM.
Various parts of the cell can also be tagged with fluorescent dyes that attach to specific molecules and emit light and aid visualisation.
132
What is an advantage of LM?
One of the main advantages of light microscopy is that it can be used to view living cells in colour.
133
What is fluorescence microscopy consist of?
Used to examine cells, cellular structures or any fluorescing material, such as stains, dyes, etc.
Fluorescent cells contain molecules that absorb light at a particular wavelength, and filters are used to block out this wavelength, allowing light emitted by the fluorescing molecules to be seen against a black background.
134
What is an advantage of fluorescence microscopy?
Fluorescence techniques allow scientists to visualise structures and materials inside cells that are usually too small to see; they can also detect particular proteins and diagnose disease.
135
What does confocal microscope consist of?
It involves passing laser light through a pinhole and lens, which provides highly focused light onto only a tiny part of the specimen.
This eliminates light reflecting from adjacent parts of the section, which would normally blur the image.
136
What is an advantage of confocal microscopy?
Allows scientists to obtain ‘optical sections’ of a cell or tissue, stained with fluorescent markers, without actually sectioning or slicing the cells.
137
What is electron microscopy?
The EM was developed in the 1930s, and focuses beams of electrons rather than light, on and through specimens.
138
What is the magnification of an EM?
Up to x300,000.
139
What is the resolution limit of an EM?
About 0.1nm (0.0001μm).
140
What are the two types of EM microscopy?
Scanning Electron Microscopy and Transmission Electron Microscopy.
141
What is Scanning Electron Microscopy? (SEM)
The SEM scans an electron beam across the surface of a specimen.
The specimen must be first coated with metal (often gold).
SEM images of surfaces are so detailed they usually appear to be three dimensional.
142
What is Transmission Electron Microscopy? (TEM)
The TEM fires an electric beam through an ultrathin slice of a specimen, creating a two-dimensional image of the ultrathin slice (less than 100nm thick).
Heavy metals are sometimes used to stain structures within a cell.
143
What environment must a specimen be in in a TEM?
The specimen must be in a vacuum in the TEM; therefore it is first chemically fixed to stop structures from collapsing, and then dehydrated with alcohol. It is then embedded in a plastic resin, sectioned with an ultramicrotome, and stained.
144
Nanometres --> micrometres:
1nm = 0.001μm
