2.1.1 Cell Structure (Foundations in Biology) Flashcards
1
Q
What are prokaryotic organisms?
A
- prokaryotic cells
- single-celled organisms
- no nucleus present
- e.g. bacteria
2
Q
What are eukaryotic organisms?
A
- eukaryotic cells
- all animal, plant, fungal and protoctist cells
They have:
- a nucleus surrounded by a nuclear envelope, containing DNA organised and wound into linear chromosomes
- contains nucleolus
- cytoplasm
- cytoskeleton
- plasma membrane
- membrane-bound organelles
- small vesicles
- ribosomes
3
Q
Draw and label a plant cell
A
4
Q
Draw and label an animal cell
A
5
Q
What are organelles?
A
- within every cell there are various organelles
- each with a specific function
6
Q
Describe the structure and function of plasma (cell surface membrane)
A
Structure:
- membrane found on the surface of animal cells and just inside the cell wall of plant cells and prokaryotic cells
- made of mainly lipids and protein
Function:
- regulates the movement of substances into and out of the cell
- also has receptor molecules, allowing it to respond to chemicals like hormones
7
Q
Describe the structure and function of the cell wall
A
Structure: - rigid structure that surrounds plant cells and fungi
- mainly made of bundles of cellulose fibres in plant cells
- made of chitin in fungi
Function:
- supports plant cells
- prevents cells from bursting when turgid
- permeabke and allow solutions to pass through
8
Q
Describe the structure and function of the nucleus, nuclear envelope and nucleolus
A
Structure:
- large organelle surrounded by a nuclear envelope, which contains many pores
- nucleus contains chromatin (made from DNA and histone proteins)
- there is the nucleolus containing RNA and does not have a membrane around it
- chromatin is genetic material, consisting of DNA wound around histone proteins
Function:
- nuclear envelope separates contents of nucleus from the rest of the cell
- some regions of the outer and inner nuclear mebranes fuse together to allow some dissolved substances and ribsomes to pass through
- pores enable larger substances, such as mRNA, to leave nucleus and some steroid hormones enter from cytoplasm
- nucleolus is where ribosomes are made
- nucleus controls the cell’s activities
- stores the organism’s genome in DNA
- transmits genetic information
- provides instruction for protein synthesis
9
Q
Describe the structure and function of lysosomes
A
Structure:
- a round organelle surrounded by a membrane, with no clear internal structure
- formed from the Golgi apparatus
- contains powerful hydrolytic (digestive) enzymes
- abundant in phagocytic cells such as, neutrophils and macrophages
Function:
- lysosomes keep the powerful hydrolytic enzymes separate from the rest of the cell
- engulf old cell organelles and foreign matter, digest them and return the digested components to the cell for reuse.
10
Q
Describe the structure and function of ribosomes
A
Structure:
- a very small organelle (20nm) that either floats free in the cytoplasm or is attached to the rough endoplasmic reticulum
- made up of proteins and RNA
- made in the nucleolus, as two separate subunits, which pass through nuclear envelope into the cytoplasm and then combine
- not surrounded by a membrane
- some remain free in cytiplasm and some attach to RER
Function:
- ribosomes bound to the exterior of the RER are mainly for synthesising proteins that will be exported outside the cell
- ribosomes free in the cytoplasm are primarily the site of assembly of proteins that will be used inside the cell
11
Q
Describe the structure and function of rough endoplasmic reticulum (RER)
A
Structure:
- a system of membranes enclosing a fluid-filled space that are continuous wuth the nuclear membrane
- surface is covered with ribosomes
Function:
- the intracellular transport system: the cisternae form channels for transporting substances from one area of a cell to another
- provides a large surface area for ribsomes, which assemble amino acids into proteins
- these proteins then actively pass through the membrane into the cisternae and are transported to the Golgi apparatus for modification and packaging
12
Q
Describe the structure and function of the smooth endoplasmic reticulum (SER)
A
Structure:
- system of membranes, containing fluid-filled cavities (cisternae) that are continuous with the nuclear membtane
- similar to rough endoplasmic reticulum, but with no ribosomes
Function:
- contains enzymes that catalyse reactions involved with lipid metabolism such as:
- synthesis of cholesterol
- synthesis of lipids/phospholipids needed by the cell
- synthesis of steroid hormones
- it is involved with absorption, synthesis and transport of lipids from the gut
13
Q
Describe the structure and function of the vesicle
A
Structure:
- a small fluid-filled sac in the cytoplasm, surrounded by a membrane
Function:
- transports substances in and out of the cell (via plasma membrane) and between organelles
14
Q
Describe the structure and function of the golgi apparatus
A
Structure:
- a group of fluid-filled, membrane-bound, flattened sacs
- vesicles are often seen at the edges of the sacs
Function:
- proteins are modified by:
- adding sugar moleculed to make glycoproteins
- adding lipids molecules to make lipoproteins
- being folded into their 3D shape
- processes and packages new lipids and proteins into vesicles that are pinched off then are:
- stored in the cell
- moved to the plasma membrane, to be incorporated or exported
- makes lysosomes
15
Q
Describe the structure and function of the mitochondrion
A
Structure:
- usually oval shaped 2-5µm long
- have a double membrane
- inner membrane is folded to form structures called cristae
- inside is the matrix, containing enzymes involved in respiration
Function:
- site of aerobic respiration where ATP is produced
- they are self-replicating, so more can be made if the cell’s energy needs to increase
- found in very large numbers in cells that are very active and require a lot of energy
16
Q
Describe the structure and function of chloroplasts
A
Structure:
- a small, flattened structure found in plant cells and in some protoctists, but a large organelle
- 4-10µm long
- surrounded by a double membrane and membranes inside called thylakoid membranes, which contain chlorophyll
- stacked up in some parts of the chloroplast to form grana
- grana are linked by lamellae
- choloroplasts contain loops of DNA and starch grains
- abundant in leaf cells, particularly palisade and mesophyll layer
Function:
- site of photosynthesis
- first stage of photosynthesis, where light energy is trappd by chlorophyll and used to make ATP, occurs in the grana
- second stage occurs in stroma
17
Q
Describe the structure and function of the centriole
A
Structure:
- small, hollow cylinders, made of microtubules , which are made of tubulin protein subunits
- consists of two bundles of microtubules are right angles to each other
- found in animal cells, but only some plant cells and maybe some unicellular green algae
Function:
- involved with the separation of chromosomes during cell division:
- before cell divides, the spindle, made of threads of tubulin, forms from the centrioles
- chromosomes attach to the middle part of the spindle and motor proteins walk along the tubulin threads, pulling the chromosomes to opposite ends of the cell
- involved in the formation of cilia and undulipodia (flagella):
- before the cilia form, the centrioles multiply and line up beneath the cell surface membrane
- microtubules then sprout outwards from each centriole, forming a cilium or flagella
18
Q
Describe the structure and function of cilia
A
Structure:
- small, hair-like structures found on the surface membrane of some animal cells
- formed from centrioles
- they have an outer membrane and a ring of nine pairs of protein microtubules inside, with two microtubules in the middle
Function:
- microtubules allow cilia to move
- moves substances along the cell surface
19
Q
Describe the structure and function of the flagellum
A
Structure:
- like cilia but longer
- stick out from the cell surface and are surrounded by plasma membrane
- same 9+2 formation as cilia
Function:
- microtubules contract to make flagellum move
- like outboard motors to propel cells forward
20
Q
Describe how organelles are involved in protein production
A
- gene has coded instructions for a protein is transcribed into mRNA
- Many mRNA are made and they pass out of the pores in the nuclear envelope to the ribosomes
- at the ribosomes, instructions are transplated and insulin molecules are assembled
- the molecules pass into the cisternae of the RER and along these hollow sacs
- vesicles with these protein molecules are pinched off from the RER and pass, via microtubules and motor proteins to the Golgi apparatus
- these vesicles fuse with the Golgi apparatus, where the molcules are modified for release
- inside vesicles pinched off from the Golgi apparatus, these molecules pass to plasma membrane
- the vesicles and plasma membrane fise and the insulin is released to the outside of the cell
21
Q
What is the cytoskeleton?
A
Structure:
- a network of protein structures within the cytoplasm consisting of:
- rod-like microfilaments made of subunits of the protein actin; they are polymers of actin and each microfilament is about 7nm in diameter
- intermediates filaments about 10nm in diameter
- straight, cyliner microtubules, made of protein subunits called tubulin, about 18-30 in diameter
- the cytoskeletal motor proteins, myosins, kinesins and dyneins, are molecular motors
- they are also enzymes and have a site that binds to and allows hydrolysis of ATP as their energy source
Function:
- the protein microfilaments within the cytoplasm give support and mechanical strength, keep the cell’s shape stable and allow cell movement
- microtubules also provide shape and support to cells and help substances and organelles to move through the cytoplasm within a cell
- they form the track along which motor proteins (dynein and kinesin) walk and drag organelles from one part of the cell to another
- they form the spindle before a cell divides. these spindle threads enable chromosomes to be moved within the cell
- microtubules also make up the cilia, flagella and centrioles
- intermediate filaments are made of a variety of proteins. they:
- anchor the nucleus within the cytoplasm
- extend between cella in some tissues, between special junctinos, enabling cell-cell signalling and allowing cells to adhere to a basement membrane, therefore stabilising tissues
22
Q
What are the four main functions of the cytoskeleton?
A
- Mechanical Strength: the microtubules and microfilaments support the cell’s organelles, keeping them in position
- Structure: They help to strengthen the cell and maintain its shape
- Aiding transport: they’re responsible for the movement of materials within the cell. they help the cell to divide (cytokinesis)
- Enabling movement: proteins of the cytoskeleton can also cause the cell to move. E.g. movement of cilia and flagella are caused by the cytoskeletal protein filaments that run through them
23
Q
Give the characteristics of prokaryotic cells
A
- extremely small cells (less than 2 um)
- DNA is circular
- no nucleus, DNA free in cytoplasm
- cell wall made of a peptidoglycan not cellulose
- few organelles and no membrane-bound organelles
- flagella made of protein flagellin
- smaller ribosomes
- have a much less well-developed cytoskeleton with no centrioles
- e.g. E.coli bacterium
some also have:
- protective waxy capsule surrounding cell wall
- small loops of DNA, called plasmids, as well as the main large loop of DNA
- flagella
- pili
24
Q
Give the characteristics of eukaryotic cells
A
- larger cells (10-100um)
- DNA is linear
- Nucleus present, DNA inside it
- no cell wall in animals, cellulose cell wall in plants and chitin cell wall in fungi
- many organelles
- flagella made of microtubule proteins in 9+2 formation
- larger ribosomes
25
Draw a bacterial cell
26
What is resolution?
- the ability of an optical instrument to see or produce an image that shows fine detail clearly
- how detailed the image is
- how well a microscope distinguishes between two points that are close together
27
How to calculate magnification
- magnification = image size / object size
28
What is magnification?
- how much bigger the image appears compared to the specimen
29
Describe the light (optical) microscope
- light microscopes use light (between 400-700nm)
- they have a lower resolution than electron microscopes - maximum resolution of about 0.2 um
- used to look at whole cells or tissues
- maximum useful magnification is around x 1500
- relatively cheap
- easy to use
- able to study whole organisms
30
Describer the laser scanning confocal microscope
- Laser scanning confocal microscope use laser beams to scan a specimen, which is usually tagged with a fluorescent dye
- causes the dye to fluoresce. light is then focused through a pinhole onto a detector. detector is hooked to a computer, generating an image, which can be 3D
- produces a much clearer image than light microscope because the pinhole means out of focus light is blocked
- can be used to look at objects at different depths in thick specimens
- high resolution and high contrast images
31
Describe electron microscopes
- they use electrons to form an image
- higher resolution than light microscopes
**Transmission electron microscope (TEM):**
- use electromagnets to focus a beam of electrons, then transmitted through specimen
- denser parts absorb more electrons, which make it darker in the image
- provides high resolution images, but can only be used on thin specimens
**- Scanning electron microscope (SEM):**
- scan a beam of electrons across the specimen
- this knocks off electrons from the specimen, which are gathered in a cathode ray tube to form an image
- show the surface of specimen and can be 3D
- lower resolution image than TEM
32
What are the maximum resolutions of the three microscopes?
Light: - 0.2 um
TEM: - 0.0002 um
SEM: -0.002 um
33
What are the maximum magnifications of the three microscopes?
Light: - x 1500
TEM: - more than 1,000,000
SEM: - less than 500,000
34
What is differential staining?
- stains are coloured chemicals which bind to molecules in or on the specimen
- some bind to specific cell structures, which stains each structure differently to allow easy identification with one preparation
35
Give examples of different types of differential staining
- acetic orcein binds to DNA and stains chromosomes dark red - eosin stains cytoplasm
- Sudan red stains lipids
- iodine in potassium iodide solution stains the cellulose in plant walls yellow and starch granules blue/black
36
Why are organelles within eukaryotic cells membrane bound?
- keeps each organelle separate from the rest of the cell, sot that it is a decrete compartment
- only eukaryotic cells have them
37
Describe the structure of function of the vacuole
_Structure:_
- surrounded by a membrane called the tonoplast and contains fluid
_Function:_
- only plant cells have a large permanent vacuole
- filled with water and solutes and maintains cell stability because it pushes against the cell wall, making the cell turgid
- this helps to support the plant if all cells are turgid
38
How do prokaryotes cells divide?
- binary fission
- do not have linear chromosomes, so cannot carry out mitosis
- however, before division, DNA is copied so that each new cells receives a large loop of DNA
