Topic 2 - Cells Flashcards
1
Q
What is the function of a nucleus?
A
Contains all of the genetic material in the cell.
2
Q
The nucleus is the site of what?
A
Protein synthesis.
3
Q
What does the nucleolus do?
A
Manufactures ribosomal RNA and ensembles the ribosomes.
4
Q
Role of the nuclear pores.
A
Allow large molecules in & out of the nucleus e.g messenger RNA.
5
Q
What is the nuclear envelope?
A
A double membrane which surrounds the nucleus.
Its outer membrane is continuous with the endoplasmic reticulum of the cell and often has ribosomes on its surface.
Contains the reactions taking place within it.
6
Q
What is the nucleoplasm found in the nucleus?
A
Granular, jelly-like material that makes up the bulk of the nucleus.
7
Q
What does mitochondria do?
A
The site of aerobic respiration.
Responsible for the production of the energy-carrier molecule, ATP, from respiratory substrates such as glucose. – because of this, the number and size of the mitochondria, and the number of their cristae, are high in cells that have a high level of metabolic activity, and therefore require lots of ATP.
8
Q
What does the Cristae (in mitochondria) do?
A
Provide a large surface area for the attachment of enzymes and other proteins involved in respiration.
(extensions of the inner membrane)
9
Q
What does the matrix (in mitochondria) do?
A
It contains proteins, lipids, ribosomes and DNA that allows the mitochondria to control the production of some of their own proteins. Many enzymes involved in respiration are found in the matrix.
10
Q
What does the rough endoplasmic reticulum (RER) do?
A
Synthesises and transports proteins, has ribosomes.
11
Q
What does the smooth endoplasmic reticulum (SER) do?
A
Synthesises, stores and transports lipids and carbohydrates, no ribosomes.
12
Q
What does the golgi apparatus do?
A
It is the sorting office & it is constantly moving and changing – directs molecules to where they are needed in the cell.
13
Q
What are lysosomes?
A
A membrane-bound organelle that releases hydrolytic enzymes.
14
Q
When are lysosomes formed?
A
When the vesicles produced by the golgi apparatus contain enzymes such as proteases and lipases.
15
Q
What are ribosomes the site of?
A
Site of protein synthesis.
16
Q
What type of cells are 80s Ribosomes found in?
A
Found in eukaryotic cells, around 25nm in diameter.
17
Q
What type of cells are 70s Ribosomes found in?
A
Found in prokaryotic cells, mitochondria and chloroplasts, is slightly smaller than 80s ribosomes
18
Q
Do eukaryotic cells have a membrane-bound nucleus?
A
Yes.
19
Q
Do prokaryotic cells have a membrane-bound nucleus?
A
No.
20
Q
When are centriples needed?
A
When the cell divides.
21
Q
What is the function of of Cytoskeleton?
A
Holds the cell organelles in specific positions.
22
Q
How do you distinguish between chloroplasts and mitochondria on a diagram?
A
Chloroplasts are bigger than mitochondria.
23
Q
What is the function of chloroplasts?
A
Absorb sunlight for photosynthesis
24
Q
What is the chloroplast envelope?
A
A double plasma membrane that surrounds the organelle. Highly selective in what it allows to enter and leave the chloroplast.
25
What is the grana in a chloroplast?
Stacks of up to 100 disc-like structures called thylakoids. These create a large surface area to absorb light. Thylakoids contain chlorophyll. The thylakoids in the grana is where the first stage of photosynthesis (light absorption) takes place.
26
What is the stroma in a chloroplast?
A fluid-filled cavity where the light independent stage of photosynthesis takes place.
27
What are cell walls in plants made from?
Cellulose middle lamellae - a thin boundary between cell walls (cement).
28
What are cell walls in fungi made from?
Chitin.
29
In Algae what is the cell wall made from?
Cellulose or glycoproteins or a mixture of both
30
What is the cell vacuole and what is the single membrane is is bounded by called?
A fluid-filled sac bounded by a single membrane called the tonoplast
31
What does a cell vacuole contain?
Cell sap which is a solution of mineral salts, sugars, amino acids, wastes and sometimes pigments such as anythocyanins.
32
In what form is the genetic material in a bacterial cells in?
A circular strand of DNA.
33
What are the separate smaller circular pieces of DNA in a bacteria cell called?
Plasmids.
34
What are plasmids extensively used for?
Vectors (carriers of genetic information) in genetic engineering.
35
Is a cell wall in a bacterial cell a physical barrier which excludes certain substances and protects against mechanical damage and osmotic lysis?
Yes.
36
What is the role of a capsule is a bacterial cell?
Protects bacterium from other cells and helps groups of bacteria to stick together for further protection
37
What is the role of the cell-surface membrane in bacterial cells?
Acts as a differentially permeable layer, which controls the entry and exit of chemicals
38
Role of plasmids in bacterial cells.
Possesses the genetic information for the replication of bacterial cells.
39
What do bacterial cells use the flagellum for?
Locomotion (only certain species).
(PROKARYOTIC CELLS CAN HAVE ONE OR MORE FLAGELLA'S)
40
True or False : Prokaryotic cells are much SMALLER than Eukaryotic cells
True.
41
Prokaryotic cells are much different form Eukaryotic cells in having :
- Cytoplasm that lacks membrane-bound organelles
- Smaller ribosomes (70s)
- No nucleus : instead they have a single circular DNA molecule that is free in the cytoplasm and is not associated with proteins
- A cell wall that contains murein, a glycoprotein.
42
What two things are viruses?
Acellular and non-living.
43
Are viruses smaller that bacteria?
Yes.
44
What do viruses contain? _ _ _
They contain nucleic acids such as DNA or RNA as a genetic material.
45
What is the protein coat in which nucleic acids are enclosed within?
A capsid.
46
Where do viruses multiply?
Inside living host cells.
47
What do lipid envelopes (if not present, Capsid) have?
Attachment proteins which are essential to allow the virus to identify and attach to a host cell.
48
What are microscopes and what do they produce?
Instruments that produce a magnified image of an object.
49
Magnification definition.
How many times bigger the image is when compared to the object.
50
What calculation do you use to work out the magnification?
Size of image / Actual size
51
How do you covert mm to um?
Times mm by 1000.
52
How do you convert um to nm?
Times um by 1000.
53
Resolution definition.
The minimum distance apart that two objects can be in order for them to appear as separate items.
54
What does the resolving power of a microscope depend on?
The wavelength or form of radiation used.
55
What is the resolution of a light (optical) microscope?
0.2um.
56
What does greater resolution mean?
Greater clarity (clearer & more precise).
57
Advantages of Light (optical) microscopes :
- Easy to use
- Portable
- Cheaper
- Can use live specimens
- Images are in colour
58
Disadvantages of Light (optical) microscopes :
- Low magnification
- Low resolution
59
What is CELL FRACTIONATION?
The process where cells are broken up an the different organelles they contain are separated out.
60
What are the 3 things you have to do to make sure organelles are healthy before separation?
Make sure the tissue is placed in an ice cold, buffered solution of the same water potential as the tissue.
61
Why does the tissue have to be ice cold?
To reduce enzyme activity that might break down the organelles.
62
Why does the tissue have to be in a buffered solution?
pH does not fluctuate - this could lead to the acids & alkalis damaging the organelles. This could be by damaging the structure or affect the functioning of enzymes.
63
What are the two stages of cell fractionation?
Homogenation & Ultracentrifugation.
64
What is homogenation?
Cells are broken up by a homogeniser (blender).
This releases the organelles from the cell.
The resultant fluid, known as homogenate, is then filtered to remove any complete cells and large pieces of debris.
65
What is Ultracentrifugation?
The process by which the fragments in the filtered homogenate are separated in a machine called a centrifuge. This spins tubes of homogenate at a very high speed in order to create a centrifugal force.
66
What is the process of Ultracentrifugation? (For animal cells)
- The tube of filtrate is placed in the centrifuge and spun at a low speed.
- The heaviest organelles, the nuclei, are forced to the bottom of the tube, where they form a thin sediment or PELLET.
- The fluid at the top of the tube (SUPERNATANT) is removed, leaving just the sediment of nuclei.
- The SUPERNATANT is transferred to another tube and spun in the centrifuge at a faster speed than before.
- The next heaviest organelles, the mitochondria, are forced to the bottom of the tube.
- This process is continued in this way so that, at each increase in speed, the next heaviest organelles is sedimented and separated out.
67
Name the four organelles from heaviest to lightest : mitochondria, nuclei, lysosomes and ribosomes.
Heaviest -
- Nuclei
- Mitochondria
- Lysosomes
- Ribosomes
Lightest -
68
What does Cell Fractionation and Ultracentrifugation enable?
A detailed study of the structure and function of organelles, by showing what isolated components do.
69
What are the two types of an Electron Microscope?
Transmission Electron Microscopes (TEM)
&
Scanning Electron Microscope (SEM)
70
How do TEMs work?
They work using a beam of electrons that is focused by electromagnets as electrons are negatively charged.
Electron beam has short wavelength, which results in high resolving power.
71
What is the resolution of a TEM microscope?
0.1nm.
72
Advantages of TEM microscopes :
- Used to view very small objects
- Allows us to see very detailed images
73
Disdvantages of TEM microscopes :
- Very expensive
- Electrons are absorbed by molecules in the air so specimens have to be viewed using a vacuum to prevent distortion
- Specimens are dead (no air) and take a long time to prepare
- Only black and white images are generated
- A complex 'staining' process is required and even rhen the image is not in colour.
74
Why do specimens need to be extremely thin? [TEM]
To allow the electron beam to pass through (PENETRATE).
75
Are the images that are produced 2D or 3D? [TEM]
2D -- Specimens must be extremely thin to allow electrons to penetrate.
76
What do photomicrographs often contain? [negative point]
Artefacts from tissue preparation.
77
Areas of the specimen that absorb electrons show up ...
... Black.
78
Areas of the specimen that allow electrons to pass through show up ...
... White.
79
How do TEMs work?
The TEM consists of an electron gun that produces a beam of electrons that is focused onto the specimen by a condenser electromagnet. In a TEM, the beam passes through a thin section or the specimen. Parts of this specimen absorb electrons and therefore appear dark. Other pans of the specimen allow the electrons to pass through and so appear bright. An image is produced on a screen and this can be photographed to give a photomicrograph.
80
The resolving power of the TEM is
0.1 nm although this cannot always be achieved in practice. WHY?
* difficulties preparing the specimen limit the resolution that can be achieved
* a higher energy electron beam is required and this may destroy the specimen.
81
Do TEMs and SEMs have practically the same limitations? except that specimens need not be extremely thin as electrons do not penetrate
Yes.
82
How do SEMs work?
Similar to a TEM, the SEM directs a beam of electrons on to the surface of the specimen from above, rather than penetrating it from below.
The beam is then passed back and forth across a portion of the specimen in a regular pattern.
The electrons are scattered by the specimen and the pattern of this scattering depends on the contours of the specimen surface.
We can build up a 3-D image by computer analysis of the pattern of scattered electrons and secondary electrons
produced.
The basic SEM has a lower resolving power than a TEM, around 20 nm, but is still ten times better than a light microscope.
83
What is the resolving power of an SEM? is it lower or higher than TEMs?
20nm , lower that TEMs.
84
When using a light microscope, what can you use when measuring the size of objects?
An eyepiece graticule.
85
What is the graticule?
A glass disc that is placed in the eyepiece of a microscope. A scale is atched on the glass disc. This scale is typically 10mm long and is divided into 100 sub-divisions. The scale is visible when looking down the eyepiece of the microscope.
86
Why does the graticule need to be calibrated for a particular objective lens?
The scale on the eyepiece graticule cannot be used directly to measure the size of objects under a microscope’s objective lens because each objective lens will magnify to a different degree.
87
What do you need to use to calibrate an eyepiece graticule?
You need to use a special microscope slide called a stage micrometer.
88
Within all multicellular organisms, can they all divide?
No.
89
Is mitosis part of the cell cycle?
Yes.
90
Is mitosis a controlled process?
Yes.
91
What does mitosis produce?
Two daughter cells that have the same number of chromosomes as the parent cell and each other.
92
What are the 5 stages of mitosis?
Interphase
Prophase
Metaphase
Anaphase
Telophase (+ Cytokinesis)
93
HOW DO YOU REMEMBER THE ORDER OF THE 5 STAGES OF MITOSIS?
IPMAT.
94
What happens during the INTERPHASE of mitosis?
The replication of DNA. The two copies of DNA after replication remain joined at a place called the centromere.
& The cell builds up energy for cell and nuclear division.
NO CHROMOSOMES ARE VISIBLE
95
What happens during the PROPHASE of mitosis?
CHROMOSOMES CONDENSE AND BECOME VISIBLE
Centrioles move to opposite poles of the cell.
Microtubules (spindle fibres) then protrude from the centrioles forming a spindle. (From each of the centrioles, spindle fibres develop, which span the cell from pole to pole. Collectively, these spindle fibres are called the spindle apparatus).
The nuclear membrane breaks down and the nucleolus disappears.
96
What happens during the METAPHASE of mitosis?
CHROMOSOMES ARE SEEN TO BE MADE UP OF TWO CHROMATIDS
Chromatids migrates towards the equator of the spindle and line up along it.
The chromatids are attached to the spindle by the centromere.
The spindle contracts slightly separating the individual chromatids.
97
What happens during the ANAPHASE of mitosis?
The centromeres break and the chromatids separate. The microtubules pull the separated chromatids towards the poles.
These are now the daughter chromosomes which will eventually be enclosed in two separate nuclei.
98
What happens during the TELOPHASE (+ CYTOKINESIS) of mitosis?
The newly formed daughter chromosomes lengthen and uncoil.
The spindle breaks and the centrioles replicate.
The nucleoli reappear and the nuclear membrane re-forms.
The cytoplasm divides in a process called cytokinesis.
99
What cell division occurs in prokaryotic cells?
Binary fission.
100
What is the process of binary fission?
* The circular DNA molecule replicates and both copies attach to the cell membrane.
* The plasmids also replicate.
* The cell membrane begins to grow between the two DNA molecules and begins to pinch inward, dividing the cytoplasm into two.
* A new cell wall forms between the two molecules of DNA, dividing the original cell into two identical daughter cells, each with a single copy of the circular DNA and a variable number of copies of the plasmids.
101
Do viruses undergo cell division? Why?
No, because they are non-living.
102
If viruses do not undergo cell division then what happens?
they replicate by attaching to their host cell with the attachment proteins on their surface. They then inject their nucleic acid into the host cell. The genetic information on the injected viral nucleic acid then provides the 'instructions' for the host cell 's metabolic processes to start producing the viral components, nucleic acid, enzymes and structural proteins, which are then assembled into new viruses.
103
How many stages does the cell cycle have?
3
I) interphase. which occupies most of the cell cycle. and is sometimes known as the resting phase because no division takes place.
2) nuclear division. when the nucleus divides either into two (mitosis) or four (meiosis).
3) division of the cytoplasm (cytokinesis), which follows nuclear division and is the process by which the cytoplasm divides to produce two new cells (mitosis) or four new cells (meiosis).
104
What is interphase also known as? (CELL CYCLE)
Resting phase as no division takes place.
105
What is the cell-surface membrane?
It is the name specifically given to the plasma membrane that surrounds cells and forms the boundary between the cell cytoplasm and the environment. It allows different conditions to be established inside and outside a cell. It controls the movement of substances in and out of the cell.
106
What do phospholipids form?
A phospholipid bilayer.
107
What are the two components to a phospholipid bilayer?
* The hydrophilic heads of both phospholipid layers point to the outside of the cell-surface membrane anracted by water on both sides.
* The hydrophobic tails of both phospholipid layers point into the centre of the cell membrane, repelled by the water on both sides.
108
What are the functions of phospholipids?
- Allow lipid-soluble substances to enter and leave the cell.
- Prevent water soluble substances entering and leaving the cell.
- Make the membrane flexible and self-sealing.
109
Why are proteins in the phospholipid bilayer?
They act to give mechanical support to the membrane or with glycolipids, act as cell receptors for molecules such as hormones.
110
What are protein channels in the cell membrane do?
Form water-filled tubes to allow water-soluble ions to diffuse across the membrane.
111
What do carrier proteins in the cell membrane do?
Bind to ions or molecules like glucose and amino acids, then change shape in order to move these molecules across the membrane.
112
What are the functions of having proteins in the membrane?
* provide structural support.
* act as channels transporting water-soluble substances across
the membrane.
* allow active transport across the membrane through carrier proteins.
* form cell-surface receptors for identifying cells.
* help cells adhere together.
* act as receptors, for example for hormones.
113
Why are cholesterol molecules in the phospholipid bilayer? Functions?
- Add strength to the membrane.
- Cholesterol molecules are very hydrophobic = prevent loss of water and dissolved ions from the cell.
- Pull together the fatty acid tails = limiting movement (reducing lateral movement).
- Make the membrane less fluid at high temperatures.
114
What are glycolipids made from?
Carbohydrate covalently bonded with a lipid. The carbohydrate portion extends from the phospholipid bilayer into
the watery environment outside.
115
What is the function of glycolipids in the phospholipid bilayer?
- Acts as recognition sites.
- Helps maintain the stability of the membrane.
- Helps cells to attach to one another and so form tissues.
116
What are glycoproteins made from?
Carbohydrate chains attached to many extrinsic proteins on the outer surface of the cell membrane.
117
What is the function of glycoproteins in the phospholipid bilayer?
- Act as recognition sites.
- Helps cells to attach to one another to form tissues.
118
What are the functions of membranes within cells?
- Controls what enters and exits in discrete organelles e.g mitochondria and chloroplasts.
- Separate organelles from cytoplasm that specific metabolic reactions can take place within them.
- Provide surfaces from which reactions can occur e.g protein synthesis using ribosomes on RER.
- Isolate enzymes that might damage the cell e.g lysosomes.
- Provide an internal transport system e.g endoplasmic reticulum.
119
Why do most molecules not freely diffuse across the cell membrane?
* not soluble in lipids and therefore cannot pass through the phospholipid layer.
* too large to pass through the channels in the membrane.
* of the same charge as the charge on the protein channels and so even if they are small enough to pass through, they are repelled.
* electrically charged (in other words are polar) and therefore have difficulty passing through the non-polar hydrophobic tails in the phospholipid bilayer.
120
What is the Fluid Mosaic Model?
A model that refers to how the lipid bilayer tends to act more like a liquid than a solid and contains a number of different components.
121
Why is the Fluid Mosaic Model called FLUID?
The individual phospholipid molecules can move relative to one another. This gives the membrane a flexible structure, that is always changing shape.
122
Why is the fluid Mosaic Model called MOSAIC?
The proteins that are embedded in the phospholipid bilayer, vary in shape, size and pattern in the same way as stones of tiles of a mosaic.
123
Diffusion definition :
The net movement of molecules or ions from a region where they are more highly concentrated to one where their concentration is lower until evenly distributed.
NO ENERGY IS NEEDED FOR DIFFUSION TO HAPPEN
124
What type of transport is diffusion an example of and what does it mean?
PASSIVE Transport, it means that energy comes from the natural inbuilt motion of particle.
125
When can diffusion only occur?
It can only occur between different concentrations of the same substance.
126
During diffusion do particle move up or down a concentration gradient?
Down.
127
When does SIMPLE diffusion occur?
When molecules diffuse directly through a cell membrane.
128
When does FACILITATED diffusion occur?
At specific points on the plasma membrane where there are specific protein molecules.
129
What is the difference between SIMPLE diffusion and FACILITATED diffusion?
In simple diffusion, molecules move without the assistance of membrane proteins, whereas in facilitated diffusion, membrane proteins assist molecules in their movement downward.
130
What does the rate of SIMPLE diffusion depend on?
= surface area
= concentration gradient
= thickness of the membrane
131
What does the rate of FACILITATED diffusion depend on?
= concentration gradient
= number of channel/carrier proteins
132
What are CHANNEL PROTEINS?
These proteins form water-filled hydrophilic channels across the membrane. They allow specific water-soluble ions to pass through.
Channels are selective - each opening in the presence of a specific ion. -- if specific ion not present = channel remains closed = control over the entry and exit.
The ions bind with the protein causing it to change shape in a way that closes it on one side of the membrane and opens it on the other side.
133
What are CARRIER PROTEINS?
Carrier proteins span the plasma membrane.
When a molecule such as glucose that is specific to the protein is present, it binds with the protein. This causes it to change shape so that the molecule is released to the inside of the membrane.
NO EXTERNAL ENERGY IS NEEDED.
The molecules move from a region where they are highly concentrated to one of lower concentration, using only the kinetic energy of the molecules themselves.
134
What do you need to remember about protein channels and carrier proteins? [BS]
Both have binding sites, but these are different to active sites.
135
What is OSMOSIS?
The passage of water from a region where it has a higher water potential to a region where it has a lower water potential through a semi-permeable membrane.
136
What does water potential mean?
Water potential is the potential of water molecules to diffuse out of or into a solution.
137
What does having a higher water potential mean?
If the water potential is low, is the value more negative?
Highest concentration of water molecules.
The value is more negative if the water potential is low.
138
What liquid has the highest water potential?
Pure water.
139
What does the RATE of osmosis depend on?
= The water potential gradient (higher water potential gradient = the faster rate of osmosis)
= Thickness of the exchange surface (thinner=faster)
= Surface area of the exchange surface (larger = faster)
140
How do you find the water potential of cells or tissues?
Place them in a series of solutions of different water potentials. Where there is no net gain or loss of water from the cells or tissues, the water potential inside the cells or tissues must be the same as that of the external solution.
141
Does osmosis require metabolic energy?
No.
142
What is osmosis in plants?
- cytoplasm is fluid (cytosol).
- surrounded by the plasma membrane.
- high pressure from cell vacuole supports the plant so it does not wilt (turgor pressure).
143
What are 3 important parts of plant cells which are involved in osmosis?
- cell wall are fully permeable to all membranes .
- the wall is strong and pushes against the cytoplasm of the cell pushing against the cell wall.
- plant develops high internal pressures in the right conditions.
144
What is TURGOR PRESSURE?
= water moves into and out of the vacuole by osmosis.
= the vacuole when normally full, presses against the cytoplasm which presses against the cell wall creating normal internal cellular pressure (TURGOR PRESSURE).
= turgor pressure in young and soft parts of plants provide support !
145
What happens if no/reduced turgor pressure?
Plant wilts.
146
What does Turgor Pressure do to help a plant cell?
Keep planet cell rigid and firm (strong).
147
Osmosis in animal cells :
Animal cells have no cell walls ...
... So never any internal pressure.
Animal cells rely more on having the same water potential in their cytoplasm as that of the surrounding fluid.
148
Do animal cells shrink when they are placed in a concentrated salt solution?
Yes.
149
Do animal cells swell and burst when they are placed in distilled water?
Yes.
150
What is ACTIVE TRANSPORT?
The movement of molecules or ions into or out of a cell from a region of lower concentration to a region of higher concentration using ATP and carrier proteins.
151
What do carrier proteins in active transport act as?
Pumps.
152
Does active transport occur against the concentration gradient?
Yes.
153
Where molecule does active transport get its metabolic energy from?
ATP.
154
Why is ATP needed in active transport?
+ co-transport
* directly move molecules
* individually move molecules using a concentration gradient which has already been set up by (direct) active transport. This is known as co-transport (A TYPE OF CARRIER PROTEINS - BIND TWO MOLECULES AT A TIME)
ATP IS NEEDED OTHERWISE IT WILL NOT WORK.
155
Why do carrier proteins use ATP during active transport?
To change their shape and allow the substance to be released on the other side.
156
What does the RATE of osmosis depend on?
= speed of individual carrier proteins (faster = faster rate of active transport)
= number of carrier proteins present (more present = faster rate of active transport)
= rate of respiration in the cell and availability of ATP -- If inherited it can not take place.
157
Where do we need active transport?
+ sodium potassium pumps
- Absorption of mineral ions into plant roots from the soil.
- Movement of sodium and potassium ions across cell membranes in nucleus and nerves.
- Reabsorption of ions in the kidney.
- Absorption of glucose and amino acids from the small intestine into the blood.
158
What is an example of a 'pump' in regards to active transport?
Sometimes more than one molecule or ion may be moved in the same direction at the same time by active transport. Occasionally, the molecule or ion is moved into a cell/organelle at the same time as a different one is being removed from it. An example of this is the sodium-potassium pump.
