Cells Flashcards
1
Q
What is a cell?
A
A cell is the basic unit of all living organisms; it is surrounded by a cell surface membrane and contains genetic material ( DNA) and cytoplasm containing organelles.
2
Q
What is an organelle?
A
A structurally and functionally distinct part of a cell.
E.g ribosomes , mitochondria
3
Q
What is a eukaryote?
A
An organism whose cells contain a nucleus and other membrane-bound organelles
4
Q
What is a prokaryote?
A
An organism whose cells do not contain a nucleus or any other membrane-bound organelles.
5
Q
What is the cell surface membrane?
A
A very thin membrane (7.5-10nm) surrounding all cells.
Found in both eukaryotic and prokaryotic cells.
6
Q
Describe the structure of the cell surface membrane.
A
At very high magnifications, it is seen to have a trilaminar appearance; two dark layers surrounding a pale interior.
Formed from a BILAYER OF PROTEINS AND PHOSPHOLIPIDS.
7
Q
What are the functions of the cell surface membrane?
A
- It is SELECTIVELY PERMEABLE: controls the exchange of substances into and out of the cell.
•Forms a barrier across which all substances entering or exiting the cell must pass. - It retains the fluid cytosol.
8
Q
What is the nucleus?
A
The largest organelle found in all eukaryotic cells, but absent from prokaryotic cells.
9
Q
What is the nuclear envelope?
A
The two membranes , situated close together, that surround the nucleus. The envelope is perforated with NUCLEAR PORES.
The outer membrane of the nuclear envelope is continuous with the RER
10
Q
What are nuclear pores?
A
Pores found on the nuclear envelope which control the exchange of materials between the nucleus and the cytoplasm.
11
Q
What are example of substances entering the nucleus via nuclear pores?
A
- Proteins ( to make ribosomes)
- Nucleotides
- ATP
- Hormones (e.g thyroid hormone T3)
- Enzymes (e.g DNA polymerases)
- Signaling molecules.
12
Q
What are examples of substances exiting the nucleus?
A
- mRNA
- tRNA
- ribosomes for protein synthesis
13
Q
Describe the hierarchy of genetic material
A
Nucleus>chromosomes> DNA (genetic material)> organs used into functional units called genes> genes control cellular activities and inheritance
Hence, the nucleus controls cellular activities.
14
Q
Why is the DNA folded and how is this achieved?
A
DNA molecules are very long and are hence folded into a more compact shape to prevent strands from becoming tangled.
This is achieved by combining HISTONE PROTEINS.
15
Q
What is chromatin?
A
A complex of DNA and Histone proteins and some RNA; material from which chromosomes are made.
They are visible as patches or fibres within the nucleus when stained.
16
Q
What are chromosomes?
A
Present in the nucleus of eukaryotic cells.
A structure made of tightly coiled chromatins visible during cell division.
17
Q
What is circular DNA? Where is it present?
A
A circular strand of DNA.
Present in: prokaryotic cells, chloroplasts and mitochondria.
18
Q
What is the nucleolus?
A
A small structure, one or more like of which is found Inside the nucleus; usually visible as a densely stained body.
19
Q
What is the function of the nucleolus?
A
To manufacture ribosomes using the information in its OWN DNA.
20
Q
Describe the structure of the nucleolus.
A
• contains a core of DNA, from one or more chromosomes, which contains the genes That code for RIBOSOMAL RNA (the form of RNA Used in the manufacture of ribosomes)
• also contains the genes for Making tRNA.
• Around the core are less densely stained regions where RIBOSOMAL SUBUNITS ARE ASSEMBLED:
Combining the rRNA with ribosomal proteins imported from the cytoplasm.
Note:
- The more ribosomes a cell makes, the larger it’s nucleolus.
- The different parts of the nucleolus only come together during the manufacture of ribosomes ( the nucleolus as a structure that disappears)
21
Q
What are the functions of the nucleus?
A
- Controls the synthesis of enzymes and hence controls all metabolic activities.
- Contains the genetic material of the cell in the form of chromosomes.
- Controls cell division.
- Carries instructions on the nuclear DNA for the synthesis of proteins.
22
Q
What is the endoplasmic reticulum describe its structure?
A
A network of flattened sacs running through the cytoplasm.
• bounded by a single membrane
• Continuous with the outer membrane of the nuclear envelope.
• the membranes of the ER form flattened compartments or sacs called CISTERNAE.
• Molecules particularly proteins can be transported through the cell inside these sacs, separated from the rest of the cytoplasm.
23
Q
Describe the structure of the RER?
A
Surface covered with ribosomes which are the sites for protein synthesis.
Note: ribosomes are found free in the cytoplasm or on the surface of the RER
24
Q
What is the function of the RER?
A
Processes, packages and transports proteins made by ribosomes.
25
What are the functions of the smooth ER?
Lacks ribosomes
Functions:
1. Synthesis of lipids, phospholipids and steroids ( cholesterol, œstrogen and testosterone)
2. A major storage site for calcium ions. Hence, smooth ER are abundant in muscle cells as calcium ions are required for muscle contraction.
3. Participates in carb metabolism.
4. Involved in drug metabolism (in the liver)
26
What are ribosomes? And state the sizes of prokaryotic and eukaryotic ribosomes
A tiny organelle found in large numbers in all cells
* not bounded by any membranes.
* found freely in the cytoplasm of ALL CELLS and the RER of EUKARYOTIC CELLS.
* prokaryotic: 20 Nm
* eukaryotic: 25 Nm
27
Describe the structure of ribosomes.
* Made of two subunits: a large subunit and a small subunit.
| * composed of almost equal amounts of rRNA and protein.
28
What are the types of ribosomes and where are they found?
80s: eukaryotic ribosomes
70s: prokaryotes, mitochondria and chloroplasts
29
What are the functions of ribosomes?
Allow all interacting molecules involved in protein synthesis to gather up in one place
30
What are examples of molecules involved in protein synthesis?
mRNA, tRNA, aminos acids and regulatory proteins.
31
What are polyribosomes?
Clusters of ribosomes formed to synthesise multiple copies of the same protein.
32
What is the Golgi apparatus/ Golgi body?
A stack of flattened membrane-bound sacs called CISTERNAE AND associated small, hollow spheres of membrane called VESICLES.
33
Describe the protein pathway across the cell.
1. Vesicles containing protein bud off form the ER
2. Vesicles fuse together to form flattened membrane-bound CISTERNAE of the Golgi body at its CIS/forming face.
3. Inside the CISTERNAE, carbohydrates may be added to proteins to form GLYCOPROTEINS.
(Golgi body contains enzymes)
4. After processing, secretory vesicles called Golgi versicles in turn bud off from the Golgi CISTERNAE at its maturing/ TRANS face.
5. These vesicles move towards the the plasma membrane and fuse with it, releasing the contents out of the cell- the secretory pathway.
Note; the process of releasing a material by a secretory vesicle out of the cell is called EXOCYTOSIS.
34
What are the functions of the Golgi apparatus?
1. Formation of primary lysosomes
2. Involved in the modification and final processing of proteins, glycoproteins and phospholipids from the ER:
- sugars are added to proteins to form GLYCOPROTEIN molecules.
- sugars are added to lipids to from glycolipids.
3. During plant cell division, the Golgi enzymes are involved in the synthesis of new cell walls.
4. In the gut and the respiratory system, goblet cells release a substance called MUCIN from the Golgi apparatus.
Mucin- main component of mucus.
35
What are the importance of glycoproteins and glycolipids?
They are important components of membranes and are important molecules in cell signaling.
36
What is the mitochondria?
The organelle in eukaryotes in which aerobic respiration takes place.
Most numerous organelles seen with light microscope.
• can move about, divide and change shape.
37
Describe the structure of the mitochondria.
* 1 micrometer In diameter
* often sausage-shaped ( circular in cross-section)
* surrounded by a double membrane (an envelope)
1. The inner membrane is folded to form finger-like cristae, which project into the interior of the mitochondrion which is called the MATRIX.
2. The space between the two membranes Is called the intermembrane space
38
What is the matrix and state it’s function.
The matrix is formed by the cristae
Function: contains the enzymes needed for aerobic respiration, producing ATP.
• small circular DNA (mitochondrial DNA) + 70s ribosomes are present in the matrix; needed for replication.
39
What are cristae and state it’s function.
Cristae are folds of the inner membrane of the mitochondrial envelope.
•stalked proteins of ATP Synthase and electron transport chains associated with aerobic respiration are found on the cristae.
40
What is the function of the mitochondria?
Main: to carry out aerobic respiration (powerhouse of the cell)
Secondary: synthesis of lipids
41
What is ATP and describe the processes involved in its formation.
ATP is the molecule (a nucleotide) that is the universal energy currency in all living things; the purpose of respiration is to make ATP.
Steps:
1. During respiration, a series of reactions take place in which energy is released from energy-rich molecules such as sugars and fats.
Note: these reactions take place in the solution in the matrix and in the inner membrane (cristae):
• the matrix contains enzymes in solution, including those in the Kreb’s cycle.
• electron carriers are found in the crisatae
2. This energy is then transferred to molecules of ATP.
42
Describe the processes involved in the release of energy from ATP.
1. Once made, ATP leaves the mitochondrion.
• ATP being a small, soluble molecule spreads rapidly through all parts of the cell where energy is needed.
2. Energy is released by breaking down ATP to ADP; a HYDROLYSIS reaction.
3. The ADP can then be recycled back into the mitochondrion for conversion back to ATP during aerobic respiration.
43
What are the uses of energy?
1. Anabolic reactions- building of larger molecules from smaller ones.
2. Active transport.
3. Muscle contraction
4. Conduction of nerve impulses
5. Homeostasis
6. Protein synthesis
7. Cell division
8. Photosynthesis
9. Cell growth
44
What are lysosomes?
* A spherical, hollow (no internal structure) organelle (specialized vesicles) found in eukaryotic cells.
* 0.1-0.5 micrometer
* contains digestive enzymes (hydrolytic/hydrolases) and has a variety of destructive functions.
Note: in plants, the large central vacuole may act as a lysosome.
45
Why must enzymes be kept separate from the rest of the cell and how is the lysosome adapted for this?
To prevent damage.
| The enzymes are retained by the SINGLE MEMBRANE Of the lysosome.
46
What are the functions of lysosomes?
Responsible for the digestion of unwanted substances and structures such as old organelles or even wholes cells.
47
What are the optimum conditions for hydrolysis?
Acidic conditions (pH 4-5) compared to the 6.5-7.0 in the cytoplasm
48
What are examples of enzymes involved in hydrolysis and where are they synthesised?
Examples: proteases, lipases and nucleases
The enzymes are synthesised on the RER and are delivered to lysosomes via the Golgi vesicles
49
Describe the role of lysosomes in getting rids of unwanted cell conponents.
Lysosomes can engulf and destroy unwanted cell components, such as molecules or organelles, that are located inside the cell (autophagy)
50
Describe the role of lysosomes in endocytosis
* Materials are taken Into the cell by endocytosis (e.g WBC engulfing bacteria by phagocytosis)
* lysosomes may fuse with the endocytic vacuoles formed and release their enzymes to digest the contents
51
Describe the role of lysosomes in exocytosis
Lysosomal enzymes may be released form the cell for extracellular digestion.
Example:
1. The replacement of cartilage by bone during development.
2. The head of sperms contain a special lysosome, the acrosomes:
Digest a path through the layers of cells surrounding the egg just before fertilisation.
52
Describe the role of lysosomes in self-digestion (autolysis)
• contents of lysosomes are released into the cytoplasm- whole cell gets digested
• this may be Part of normal development;
Example:
1. Tadpole tail being reabsorbed during metamorphosis
2. When uterus is restored to it’s normal size after pregnancy
• also occurs after the death of an individual as membranes lose their partial permeability.
53
What are microtubules?
* Long, riding, hollow tubes made up of a protein called TUBULIN in the cytoplasm of most eukaryotic cells.
* 25 nm in diameter
54
What is the cytoskeleton and what is it made up of?
An essential structure component which helps determine cell shape.
Formed from microtubules together with actin filaments and intermediate filaments.
55
Describe the structure of microtubules.
1. Made from a- and B- tubulin molecules which combine to form DIMERS (double molecules)
2. DIMERS are joined end to end to form long PROTOFILAMENTS (by polymerisation)
3. 13 protofilaments line up alongside each other *in a ring to form a cylinder with a hollow centre*- a microtubule.
Has a helical pattern.
56
What are the functions of microtubules?
1. Forms part of the cytoskeleton (mechanical furniture of support)
2. Forms an intracellular transport system for the movement of structures (e.g Golgi vesicles during exocytosis, secretory vesicles and other organelles)
3. During cell division, a spindle made of microtubules is used for the separation of chromosomes or chromatins.
4. Form part of the structure of centrioles
5. Form an essential part of the mechanism involved in the beating movement of cilia and flagella.
57
What are MTOCs?
Special locations by which the assembly of microtubules fron tubulin molecules is controlled.
58
What are centrioles?
•One of two small, hollow cylindrical fibers made from microtubules, found just outside the nucleus in ANIMAL cells, in a region known as the CENTROSOME.
* 500 nm long (only visible with electron microscope)
* absent from most plant cells
59
What is the centrosome?
The main MTOC in animal cells
60
Describe the structure of centrioles
* It is a hollow cylinder formed from a ring of short microtubules.
* Eacg centrioles contains 9 triplets of microtubules.
61
What is the function of microtubules?
Give rise to basal bodies of cilia and flagella. The microtubules that extend from the cilia and flagella are essential for the beating movement.
62
What is the cilia/cilium
* Whip-like structures projecting from the surface of many animal cells And the cells of many unicellular organisms.
* they beat, causing locomotion or the motion of fluid across the cell surface.
* short and Often numerous
63
What are the flagella/ flagellum
* Whip-like structures projecting from the surface of some animal cells and the cells of many unicellular organisms.
* they beat, causing locomotion or the movement of fluid across the cell surface.
* Identical structure to cilia but longer.
* long and usually one or two found per cell.
Note: both cilia and flagella are surrounded by an EXTENSION OF THE CELL SURFACE MEMBRANE.
64
Describe the structure of cilia
•Composed of over 600 polypeptides. This complexity results in very fine control in how they beat
•Cilia have 2 central microtubules and a ring of 9 microtubule doublets ( MTDs) around the outside.
( 9 + 2 structure)
65
Describe the structure of MTDs
* Each MTD contains an A and B microtubule.
* the wall of the A microtubule is a complete ring of 13 protofilaments.
* the B microtubule attached is an incomplete ring with 10 protofilaments.
• A microtubules has inner and outer arms made of a protein called DYNEIN.
- Connect with B microtubules of neighboring MTDs during beating.
The whole cylindrical structure inside the cell surface membrane is called the AXONEME
66
What is the basal body of cilia and flagella and how are they formed?
Structure found at the base of cilia and flagella which is identical in structure to the centriole.
Centrioles replicate themselves to form these basal bodies, and cilia and flagella grow from these basal bodies
67
Describe the beating mechanism of cilia and flagella.
* Caused by the Dynein arms making contact with, and moving along neighboring microtubules.
* this produces the force needed for cilia to beat
* as neighbouring MTDs slide past each other, the sliding motion is converted to bending of other parts.
68
What are the functions of cilia and flagella?
1. If the cell is attached to something so that it cannot move>fluid will move past the cell
2. If the cell is not attached> cell swims through the fluid.
Unicellular organism use the beating action of cilia and flagella for locomotion.
69
State the functions of cilia in vertebrates.
1. Beating cilia are found in some epithelial cells, such as those lining the airways: maintain the flow of mucus which removes debris such as dust and bacteria from the respiratory tract.
2. Help to move egg cell and sperm in the Fallopian tubes.
70
What are microvilli? Give examples of where they can be found
Small, finger-like extensions of the cell surface membrane which increase the surface area of the cell for more efficient absorption and secretion as they can accommodate more CHANNEL PROTEINS.
Examples:
1. In epithelial cells (small intestine)
2. Réabsorption in the proximal convulated tubule of the kidney
71
What is the chloroplast?
An organelle bounded by an envelope in which photosynthesis takes place in eukaryotes.
* elongated shape (3-10 micrometer)
* found in the green parts of the plants, mainly the leaves.
* large organelle that can easily be seen with the light microscope. Grana are also visible
72
What are grana?
Stack of membranes in the chloroplast that contain the pigment chlorophyll (absorbs light during photosynthesis)
73
Describe the function of chloroplasts.
Main function: to carry out photosynthesis.
1. During the first stage ( the LIGHT-DEPENDENT STAGE), light energy is absorbed by chlorophyll ( found on the membranes of the chloroplast)
2. The membrane system consists of flattened fluid filled sacs called thylakoids- responsible for the LIGHT DEPENDENT REACTIONS of photosynthesis.
Thylakoids: a flattened, membrane-bound, fluid filled sac responsible for the light dependent reactions of photosynthesis in the chloroplast.
3. In places, thylakoids form flat, disc-like structures that stack up like piles of coins, forming GRANA.
Grana are joined together by LAMELLAE (thin, flat thylakoid membranes)
4. The second stage uses the energy and reducing power generated during the first stage to convert carbon dioxide into sugars.
This takes place in the STROMA.
Note: light-dependent stage: thylakoids
Light independent stage (Calvin cycle): stroma
The 1 micrometer thickness aids the fast diffusion of ATP.
74
What is the stroma and state it’s role.
A colorless, gelatinous matrix containing the enzymes required for the light independent stage of photosynthesis.
1. the sugars formed are stored in the form of STARCH GRAINS in the stroma
2. lipid droplets are also found in the stroma (appear as black spheres)
- Act as reserved for making membranes or are formed from the breakdown of internal membranes.
3. Small circular DNA molecules and 70s ribosomes (seen as black dots ) are present in the stroma.
- Allows for chloroplast proteins to be made.
75
What are cell walls and describe its structure.
Structure:
• it is a rigid wall: contains fibers of the polysaccharide cellulose.
• May be reinforced with extra cellulose or a hard material called lignin for extra strength.
• Freely permeable allowing free movement of molecules and ions through to the cell surface membrane
76
What are the functions of the Cell wall.
1. Provides mechanical strength and support to the cell.
2. Gives the plant cell a fixed shape.
3. Prevents the plant cell from bursting.
77
What are plasmodesmata.
* Pore-like structures found in plant cell walls.
* fine strands of cytoplasm lined with the cell surface membrane.
* contain smooth ER
78
What are the functions of plasmodesmata.
1. Facilitates communication and coordination between plant cells since molecules and ions do not have to cross the cell surface membrane.
2. Allow free passage of water from cytoplasm to cytoplasm without passing through the cell surface membrane. SYMPLAST PATHWAY.
3. Sieve plate pores of Phloem sieve tubes are formed from plasmodesmata which allows the movement of cell sap.
79
How do plasmodesmata bring about their effect?
Plasmodesmata if neighbouring plant cells line up to form tube-like pores through the cell walls, allowing the controlled passage of materials from one cell to the other.
80
What is a vacuole?
A fluid filled sac bounded by single membrane.
81
Give examples of vacuoles in plant and animal cells.
Animal vacuoles: phagocytic vacuoles, food vacuoles and autophagic vacuoles.
Plant: large central vacuole.
82
Describe the structure of the large central vacuole.
* A sac in plant cells surrounded by the Tonoplast – a selectively permeable single membrane.
* retains the fluid cell sap.
83
What is cell sap?
A concentrated solution of mineral salt, sugars, organic acids, oxygen, carbon dioxide, amino acids, wastes [example tannins] and sometimes pigments called anthocyanins.
84
Describe the function of the vacuole in the support of the plant cell.
The cell sap is concentrated:
1. Water enters by osmosis, inflating the vacuole and causing a buildup of pressure.
2. A fully inflated cell is said to be turgid. Turgidity helps to support stems of plants [prevents wilting)
85
State the lysosomal activity of the large central vacuole.
Plant vacuoles may contain Hydrolases and act as lysosomes
86
Describe the function of vacuoles as food reserves.
Example:
1. sucrose in sugar beets or mineral salts may be stored in the vacuoles.
2. Proteins-storing vacuoles are common in seeds.
87
Describe the function of vacuoles a storages for waste products and secondary metabolites.
Waste products: calcium oxalate, tannins.
Storage of secondary metabolites:
Examples
1. Anthocyanins are pigments for the color of fruits and flowers. They attract pollinators and seed dispersers
2. Certain alkaloids and tannins deter herbivores from eating the plant.
3. Latex-milky fluid- accumulate in the vacuole
88
Describe the function of the large central vacuole in the growth of the plant cell.
Osmotic uptake of water into the vacuole is responsible for most of the increase in volume of plant cells during growth. The vacuole occupies up to a third of the cells total volume.
89
Describe the characteristics of prokaryotes. (Check diagram)
1. Genetic material not package within a membrane-bound nucleus and is usually circular (Eukaryotic nuclei contain linear chromosomes)
2. Lack membrane-bound organelles.
3. Contain 70s ribosomes
90
What are bacteria?
A group of single celled prokaryotic microorganisms; they have a number of characteristics,such as the ability to form pores, which distinguishes them from the other group of prokaryotes called Archae
91
What are the main features of a bacteria?
1. Cell wall
2. Cell surface membrane
3. Cytoplasm (lacks any double membrane-bound organelle)
4. Ribosomes(70s)
4. Circular DNA
5. Plasmids
6. Flagellum
7. Infolding of the cell membrane
92
Describe the structure Of the cell wall in bacteria.
Made from strengthening material called peptidoglycan
93
What is peptidoglycan?
A polysaccharide combine with amino acids ;it makes the bacterial cell wall more rigid.
Aka murein
94
State features of the circular DNA in bacteria.
* found in a region called nucleoid, which contains proteins and small amounts of RNA
* Not surrounded by double membrane
* More than one copy may be present
95
What are plasmids?
* A small circular piece of DNA separate from the main DNA of the bacterium (not its main chromosomes]
* often contain genes that provide resistance to antibiotics.
96
What are features of plasmids?
1. Contains only a few genes.
2. Many may be present in a given cell.
3. Can replicate independently of the chromosomal DNA and can spread rapidly from one bacterium to another.
4. Plasmid DNA is not associated with proteins (Naked DNA)
97
Describe the features of the flagellum in bacteria
* How much simpler structure than eukaryotic flagella
* A simple hollow cylinder made of identical protein molecules
* Waved-shaped and works by rotating at its base like a propeller to push the bacterium through it’s liquid environment. Debacterian moves forward with a corkscrew-shaped motion
98
What is the importance of the infolding of the cell membrane in bacteria?
1. Provides an extra surface where biochemical reactions can take place.
Example: blue-green bacteria
Infolded cell membrane contains photosynthetic pigments.
2. In some bacteria, nitrogen fixation takes place on the infolded cell membrane.

99
What are pilli?
Fine protein rods that very in length and stiffness.
100
Check difference between prokaryotes and eukaryotes, an animal and plant cells
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