semester one final Flashcards
1
Q
Cell theory
A
- all living things are composed of cells (or cell products)
- the cell is the smallest unit of life
- cells only arise from pre-existing cells
2
Q
What common features do cells share?
A
- every living cell is surrounded by a membrane, which separates the cell contents from everything else outside
- cells contain genetic material which stores all of the instructions needed for the cell’s activities
- many of these activities are chemical reactions, catalysed by enzymes produced inside the cell
- cells have their own energy release system that powers all of the cell’s activities
3
Q
What are the three levels of magnification on a typical high school microscope?
A
- x40 (low power)
- x100 (medium power)
- x400 (high power)
4
Q
What is the formula to calculate magnification?
A
size of image/actual size of specimen
5
Q
Explain striated muscle as an atypical example which questions the cell theory
A
- building blocks of striated muscle are muscle fibres (similar to cells)
- muscle fibres are surrounded by a membrane and are formed by division of pre-existing cells; they have their own genetic material and their own energy release system
- however, they have an average length of 30mm in humans, whereas other cells typically have a size of less than 0.03mm and have multiple nuclei
6
Q
Explain fungi as an atypical example of a cell which questions the cell theory
A
- in some types of fungi, the hyphae are divided up into small cell-like sections by cross walls called septa
- in other types of fungi, however, there are no septa and each hypha is an uninterrupted tube-like structure with many nuclei spread along it
7
Q
Explain algae as an atypical example of a cell which questions the cell theory
A
- algae are organisms that feed themselves by photosynthesis and store their genes inside nuclei
- many algae consist of one microscopic cell
- giant algae can grow to a length as much as 100mm despite only having one nucleus
8
Q
Outline the seven functions of life
A
- Nutrition: obtaining food, to provide energy and the materials needed for growth
- Metabolism: chemical reactions inside the cell, including cell respiration to release energy
- Growth: an irreversible increase in size
- Response: the ability to react to changes in the environment
- Excretion: getting rid of the waste products of metabolism
- Homeostasis: keeping conditions inside the organism within tolerable limits
- Reproduction: producing offspring either sexually or asexually
Note: Unicellular organisms must carry out all functions of life in the one cell
9
Q
Limitations on cell size
A
- surface area to volume ratio is important in the limitation of cell size
- large numbers of chemical reactions take place in the cytoplasm of the cells (metabolism)
- the rate of the reactions (metabolic rate) is proportional to the volume of the cell
- substances used for the reactions must be absorbed by the cell and the waste products must be removed; the rate at which substances cross this membrane depends on its surface area
- surface area:volume ratio is also important for heat production and loss
10
Q
Outline the ways in which Paramecium demonstrates the functions of life
A
- Paramecia are surrounded by small hairs called cilia which allow it to move (responsiveness)
- Paramecia engulf food via a specialised membranous feeding groove called a cytostome (nutrition)
- Food particles are enclosed within small vacuoles that contain enzymes for digestion (metabolism)
- Solid wastes are removed via an anal pore, while liquid wastes are pumped out via contractile vacoules (excretion)
- Essential gases enter (e.g. O2) and exit (e.g. CO2) the cell via diffusion (homeostasis)
- Paramecia divide asexually (fission) although horizontal gene transfer can occur via conjugation (reproduction)
11
Q
Cell differentiation
A
- specialized tissues can develop by cell differentiation in multicellular organisms
- different cells perform different functions
- often a group of cells specialize in the same way to perform the same function (tissue)
- the development of cells in different ways to carry out specific functions is called differentiation
- involves the expression of some genes and not others in a cell’s genome (cells have all genes needed to specialize in every possible way but only expresses certain ones)
12
Q
Electron microscopes
A
- much higher resolution than light microscopes
- reveal the ultrastructure of cells
- needed to see viruses with diameter of 0.1 micrometres
13
Q
Resolution
A
Making the separate parts of an object distinguishable by eye
14
Q
Prokaryotes
A
- simple cell structure without compartments
- no nucleus; has nucleoid instead which contains DNA
- DNA not associated with proteins
- cell wall
- do not have crytoplasmic organelles apart from ribosomes
- ribosomes are 70S (smaller than those in eukaryotoes)
15
Q
How do prokaryotes divide?
A
- binary fission
- used for asexual reproduction
- circular chromosome is replicated and the two copies of the chromosome move to opposite ends of the cell
- division of the cytoplasm
- each of the daughter cells contains one copy of the chromosome so they are genetically identical
16
Q
Eukaryotes
A
- compartmentalized cell structure, meaning that the cell is divided up by single or double membranes into compartments
- has nucleus
- DNA associated with histone proteins
- organelles in the cytoplasm (‘compartments’)
- ribosomes are 80S (bigger than those in prokaryotes)
17
Q
Advantages to being compartmentalized
A
- enzymes and substrates for a particular process can be much more concentrated than if they were spread throughout the cytoplasm
- substances that could cause damage to the cell can be kept inside the membrane of an organelle (ie. lysosome)
- conditions such as pH can be maintained at an ideal lvel for a particular process, which may be different to the levels needed for other processes in a cell
- organelles with their contents can be moved around within the cell
18
Q
What are palisade mesophyll cells of the leaf and what organelles does it contain?
A
- the cell type of the leaf that carries out the most photosynthesis
- shape is rougly cylindrical
- contains the following
1. cell wall
2. plasma membrane
3. chloroplast
4. mitochondrion
5. vacuole
6. nucleus
19
Q
Hydrophilic
A
- substances that are attracted to water
- all substances that dissolve in water are hydrophilic, including polar molecules such as glucose and chloride ions
- substances that water adheres to (ie. cellulose) are also hydrophilic
20
Q
Hydrophobic
A
- substances that are insoluble in water, but dissolve in other solvents
- molecules that are non-polar are hydrophobic
- all lipids are hydrophobic
21
Q
Amphipathic
A
Substances that are partially hydrophilic and partially hydrophobic (ie. phospholipid)
22
Q
What is a phospholipid bilayer?
A
- double layers formed by phospholipids
- stable structure
- form the basis of all cell membranes
23
Q
Why do phospholipids form bilayers in water?
A
- phospholipids form bilayers in water due to the amphipathic properties of phospholipid molecules
- phosphate group is hydrophilic
- hydrocarbon tails are hydrophobic
- when mixed with water, the phosphate heads are attacted to the water by the hydrocarbon tails are attracted to each other
- thus, the phospholipids form double layers called phospholipid bilayers
24
Q
What was the Davson-Danielli model?
A
- layers of protein adjacent to the phospholipid bilayer on both sides of the membrane
- appeared to be supported by electron micrographs of membranes which showed two dark lines with a lighter band between (railroad track appearance)
25
What were the problems with the Davson-Danielli model?
1. Freeze-etched electron micrographs
- rapid freezing of cells and then fracturing them
- fracture occurs along lines of weakness, including the centre of membranes
- globular structures scattered through free-etched images of the centre of membranes were interpreted as transmembrane proteins
2. Structure of membrane proteins
- proteins extracted from membranes were found to be varied in size and globular in shape (unlike the type of structural proteiin that would form continuous layers)
3. Fluorescent antibody tagging
- red/green fluorescent markers were attached to antibodies that bind to membrane proteins
- memrane proteins of some cells were tagged with red markers and others with green markers
- the cells were fused together and within 40 minutes, the red/green were mixed together showing that membrane proteins are free to move within the membrane rather than being fixed in a peripheral layer
26
What are some functions of membrane proteins?
- Hormone binding sites
- Enzymes
- Electron carriers
- Channels for passive transport
- Pumps for active transport
(Happy Elephants Eat Chocolate Pie)
27
Integral membrane proteins
- hydrophobic on at least part of their surface
- embedded in the hydrocarbon chains in the centre of the membrane
- many are transmembrane (they extend across the membrane, with hydrophilic parts projecting through hte regions of phosphate heads on either side)
28
Peripheral membrane proteins
- hydrophilic on their surface
- not embedded in the membrane
- most are attached to the surface of integral proteins
- attachment is often reversible
- some have a single hydrocarbon chain attached to them which is inserted into the membrane, anchoring the protein to the membrane surface
29
What are three components of animal cell membranes?
phospholipids, proteins, cholesterol
30
What is cholesterol?
- a component of animal cell membranes
- a type of liquid belonging to a group of substances called 'steroids'
- most of the molecule is hydrophobic so it is attracted to the hydrophobic hydrocarbon tails, but one end of the cholesterol has a hydroxyl group which is hydrophilic (so it is attracted to the phosphate heads)
- chloesterol molecules are therefore positioned between phospholipids in the membrane
31
What is the role of cholesterol in membranes?
- disrupts the regular packing of the hydrocarbon tails of phospholipids, so prevents them from crystallizing and behaving as a solid
- however, it also restricts molecular motion and therefore the fluidity of the memrane
- it also reduces the permeability to hydrophilic particles such as sodium ions and hydrogen ions
- due to its shape, cholesterol can help membranes to curve into a concave shape, which helps in the formation of vesicles during endocytosis
32
Endocytosis
- a process by which large substances (or bulk amounts of smaller substances) enter the cell without crossing the membrane
- results in the formation of a vesicle containing the materials that were outside of the cell
- this process is also used by some types of white blood cells in order to ingulf pathogens and kill them
- it is possible because of the fluidity of membranes
33
What are the two main types of endocytosis?
Phagocytosis – The process by which solid substances are ingested (usually to be transported to the lysosome)
Pinocytosis – The process by which liquids / dissolved substances are ingested (allows faster entry than via protein channels)
34
Exocytosis
- a process by which large substances (or bulk amounts of small substances) exit the cell without crossing the membrane
- a vesicle fuses with the membrane and the contents are released outside the cell
- this process can be used to release useful enzymes (referred to as 'secretion') or expel waste products
- it is possible because of the fluidity of membranes
35
Difussion
- the spreading out of particles in liquids and gases
- occurs because particles are in random motion
- more particles move from an area of higher concentration to an area of loewr cocnentration
- therefore, movement down the concentration gradient
- passive process (energy not consumed)
36
List 4 methods by which particles can move across membranes
simple diffusion, facilitated diffusion, osmosis, active transport
37
Simple difussion
- movement of particles across the membrane, down the concentration gradient
- involves particles passing between phospholipids in the membrane
- can only occur if the phospholipid bilayer is permeable to the particles
- non-polar particles (ie. oxygen) can diffuse into the cell esaily/passively if there is a higher concentration outside the cell than inside it
38
Facilitated diffusion
- some particles (ie. ions) cannot diffuse between phospholipids
- channels help these particles to pass through the membrane from a higher concentration to a lower concentration
39
Osmosis
- water is able to move in and out of most cells freely
- the net movement of water molecules is called osmosis
- osmosis is caused by differences in the concentrations of substances dissolved in water
- water moves from areas of low solute concentration to areas of high solute concentration
- passive process
40
Active transport
- moving against the concentration gradient (ie. moving from an area of low concentration to an area of high concentration)
- energy (ATP) and pump proteins are required
41
What is the purpose/function of sodium-potassium pumps and potassium channels?
- The axons of nerve cells transmit electrical impulses by translocating ions to create a voltage difference across the membrane
- At rest, the sodium-potassium pump expels sodium ions from the nerve cell, while potassium ions are accumulated within
- When the neuron fires, these ions swap locations via facilitated diffusion via sodium and potassium channels
42
Explain how sodium-potassium pumps work
- sodium-potassium pump is an integral protein that exchanges 3 sodium ions (moves out of cell) with two potassium ions (moves into cell) against the concentration gradient
- thus, the process of ion exchange is active transport and requires energy
- the following occurs:
1. Three sodium ions bind to intracellular sites on the sodium-potassium pump
2 .A phosphate group is transferred to the pump via the hydrolysis of ATP
3. The pump undergoes a conformational change, translocating sodium across the membrane
4. The conformational change exposes two potassium binding sites on the extracellular surface of the pump
5. The phosphate group is released which causes the pump to return to its original conformation
6. This translocates the potassium across the membrane, completing the ion exchange
43
Explain how potassium channels work
- each potassium channel conists of four protein subunits with a narrow pore between them that allows potassium ions to pass in either direction
- while potassium ions are small enough to fit through the pores, if they dissolve and bond with water, they become too large to fit
- thus, in order for the potassium ion to fit through the channel, energy is used to break the bond between the potassium ion and water
- the potassium ion temporarily bonds to the amino acid sequence in the narrowest part of the channel pore
- after the potassium ion passes through the channel, it bonds with water again
- since the potassium channels in the axon are voltage gated, they only open when there is a net positive charge inside the axon
- closes rapidly due to an extra globular protein subunit/ball, attached by a flexible chain of amino acids; the ball can fit inside the open pore milliseconds after it opens and then it remains there until the channel returns to its original state
44
Hypertonic
- has a higher osmolarity
| - water moves by osmosis to the hypertonic solution
45
Isotonic
- has the same osmolarity
| - therefore, water does not move by osmosis
46
Osmolarity
the total concentration of osmotically active solutes, measured in osmoles or milliosmoles
47
Preventing osmosis
- store tissues/organs in solutions that are isotonic to the cytoplasm
48
How are cells formed?
- division of pre-existing cells
49
Pasteur's experiments
- proof that spontaneous generation of cells and organisms does not now occur on Earth
- used swan-necked flasks and placed broth inside of them, melting the glass and bending it into a variety of shapes
- broth in some flasks were boiled (to kill any organisms), some were left unboiled for controls
- fungi/organisms appeared in the unboiled flasks but none appeared in the boiled flasks
- this proved that even with contact to air, spontaneous generation would not occur
- when the necks of the flasks were snapped, organisms/fungi began to grow in the boiled flasks
50
Endosymbiotic theory
- states that mitochondria and chloroplasts were once free-living prokaryotic organisms
- mitochondria had developed the process of aerobic cell respiration and chloroplasts had developed photosynthesis
- larger prokaryotes that could only respire anaerobically took them in by endocytosis
- instead of killing/digesting the smaller prokaryotes (ie. mitochondria/chloroplasts), they allowed them to continue to live in their cytoplasm
51
Evidence for the endosymbiotic theory
chloroplasts/mitochondria:
- have their own genes, on a circular DNA molecule like that of prokaryotes
- have their own 70S ribosomes the size and shape typical of some prokaryotes
- transcribe their DNA and use mRNA to synthesize some of their own proteins
- can only be produced by division of pre-existing mitochondria and chloroplasts
52
Mitosis
- the division of the nucleus into two genetically identical daughter nuclei
53
List the stages of mitosis in order
(interphase occurs before prophase but is not considered a stage of mitosis)
1. prophase
2. metaphase
3. anaphase
4. telophase
(cytokinesis occurs after telophase but is not considered a stage of mitosis)
54
Interphase
- a very active phase of the cell cycle with many processes occuring in the nucleus and cytoplasm
- number of mitochondria in the cytoplasm increase
- in plant/algae cells, the number of chloroplasts also increase; they also synthesize cellulose and use vesicles to add it to their walls
- consists of three phases, G1 phase, S phase and G2 phase.
- G1: cellular comtents apart from the chromosomes are duplicated
- S: each of the chromosomes is duplicated
55
Supercoiling
- repeated coiling of the DNA molecule to make the chromosome shorter and wider
- histones (protein) in eukaryote chromosomes help with supercoiling and enzymes are also involved
56
List the phases of mitosis in sequential order
prophase, metaphase, anaphase, telophase
57
Prophase
- the chromosomes become shorter and fatter by coiling
- to become short enough, they have to coil repeatedly (supercoiling)
- the nucleolus breaks down
- microtubules grow from structures called microtubule organizing centres (MTOC) to form a spindle-shaped array that links the poles of the cell
- at the end of this phase, the nuclear membrane breaks down
58
Metaphase
- microtubules continue to grow and attach to the centromeres on each chromosome
- the two attachment points on opposite sides of each centromere allow the chromatids of a chromosome to attach to microtubules from different poles
- the microtubules are all put under tension to test whether the attachment is correct
- this happens by shortening of the microtubules at the centromere
- if attachment is correct, the chromosomes remain on the equator of the cell
59
Anaphase
- each centromere divides, allowing the pairs of sister chromatids to separate
- the spindle microtubules pull them rapidly towards the poles of the cell
- mitosis produces two genetically identical nuclei because sister chromatids are pulled to opposite poles
- this is ensured by the way that the spindle microtubules were attached in metaphase
60
Telophase
- chromatids have reached poles and are now called chromosomes
- at each pole, the chromosomes are pulled into a tight group near the MTOC and a nuclear membrane reforms around them
- the chromosomes uncoil and a nucleolus is formed
- by this stage, the cell is usually already dividing and the two daughter cells enter interphase again
61
Mitotic index
- the ratio between the number of cells in mitosis in a tissue and the total number of observed cells
- can be calculated by dividing the number of cells in mitosis by the total number of cells
62
Cytokinesis
- refers to the process of cell division
- occurs after mitosis
- different in plant and animal cells
63
Cytokinesis in animal cells
- plasma membrane is pulled inwards around the equator of the cell to form a cleavage furrow
- this is accomplished using a ring of contractile proteins, actin and myosin
- when the cleavage furrow reaches the centre, the cell is pinched apart into two daughter cells
64
Cytokinesis in plant cells
- vesicles are moved to the equator where they fuse to form tubular structures across the equator
- with the fusion of more vesicles, these tubular structures merge to form two layers of membrane across the whole of the equator, which develop into the plasma membranes of the two daughter cells and are connected to the existing plasma membranes at the sides of the cell, completeing the divison of the cytoplasm
- next, pectins/other substances are brought in vesicles and deposited by exocytosis between the two new membranes
- this forms the middle lamella that will link the new cell walls
- both of the daughter cells bring cellulose to the equator and deposit it by exocytosis adjacent to the middle lamella
- thus, each cell builds its own cell wall adjacent to the equator
65
Singer-Nicolson
modern day cell membrane diagram
66
Pasteur
Investigated why beer vinegar and wine went sour. Designed experiments that challenged the theory of spontaneous generation. He discovered that if he boiled a substance in a swan neck vase there would be no microbial growth. However, if he broke the neck of shock the substance, microbial growth would begin
67
Crick and Watson
One of the first scientist to look into DNA. Used model building and trial and error to eventually get an accurate model of the double helix DNA. However they utilized other resources, like Franklin's x-ray to achieve this conclusion
68
Florey and Chain
They injected eight mice with the bacteria, and four of them were further injected with penicillin and the other four were not. Three out of four of the injected mice survived, however the other four died. They concluded that penicillin was able to fight viruses and thus tried on humans. However this did not work because they ran out of the drug. Later on this was called unethical
69
Franklin and Wilkins
```
Rosalind Franklin and Maurice Wilkins used a method of X-ray diffraction to investigate the structure of DNA (photo 51)
they discovered:
- twists every 34 angstrom
-dna forms a helix
-10 bases per twist
-dna is double stranded
-phosphates on the outside
```
70
Hershey and Chase
In 1952, Alfred Hershey and Martha Chase conducted a series of experiments to prove that DNA was the genetic material
Viruses (T2 bacteriophage) were grown in one of two isotopic mediums in order to radioactively label a specific viral component
Viruses grown in radioactive sulfur (35S) had radiolabelled proteins (sulfur is present in proteins but not DNA)
Viruses grown in radioactive phosphorus (32P) had radiolabeled DNA (phosphorus is present in DNA but not proteins)
The viruses were then allowed to infect a bacterium (E. coli) and then the virus and bacteria were separated via centrifugation
The larger bacteria formed a solid pellet while the smaller viruses remained in the supernatant
The bacterial pellet was found to be radioactive when infected by the 32P–viruses (DNA) but not the 35S–viruses (protein)
This demonstrated that DNA, not protein, was the genetic material because DNA was transferred to the bacteria
71
metabolism
two key functions:
- They provide a source of energy for cellular processes (growth, reproduction, etc.)
- They enable the synthesis and assimilation of new materials for use within the cell
72
anabolism
Anabolic reactions describe the set of metabolic reactions that build up complex molecules from simpler ones
73
catabolism
Catabolism is the breakdown of complex molecules into simpler molecules including the hydrolysis of macromolecules into monomers
74
hydrogen bonding
Hydrogen bonding and dipolarity explain the cohesive, adhesive, thermal and solvent properties of water
75
endosymbiotic theory
the theory that an early prokaryotic cell evolved into a Eukaryote cell
- oxygen bacteria = mitochondria
- photosynthesis bacteria = chloroplast
- still happening today
