2. Cells Flashcards
What is a Eukaryotic cell ?
A cell that has a distinct nucleus and possesses membrane-bound organelles
What is the function of the nucleus?
- Control centre of the cell, through the production of mRNA and tRNA
- Contains the genetic material of the cell in the form of DNA and chromosomes
- Manufacture RNA
What is the nuclear envelope?
-A double membrane surrounding the nucleus
-Outer membrane is continuous with the Endoplasmic Reticulum of the cell and will often have ribosomes on its surface
What is the function of the nuclear envelope?
-Controls the entry and exit of materials
- Contains reactions taking place within it
What are the function of the Nuclear Pores?
Allows passage of large molecules such as messenger RNA, out of the nucleus.
What is Nucleoplasm
Granular, jelly-like material that makes up the bulk of the nucleus
What is the nucleolus?
Small spherical region within the nucleoplasm
There may be multiple in the nucleus
What is the function of the nucleolus?
Manufactures ribosomal RNA and assembles ribosomes
Describe the structure of a chromosome
Consists of protein-bound, linear DNA
Chromatin is the material that makes up chromosomes
What is the function of the mitochondria
Site of Aerobic Respiration
Responsible for the production of the energy-carrier molecule ATP
What is the function of the double membrane of a mitochondrion?
Controls entry and exit of material
The inner membrane is folded to form extensions called Cristae
What is the function of the Cristae?
Provide large surface area for attachment of enzymes and other proteins required in respiration
What is the function of the matrix within the mitochondrion?
It contains proteins, lipids, ribosomes and DNA and controls the production of some of the mitochondrion proteins.
It is also the location of many enzymes involved in respiration
Describe the structure of the Endoplasmic Reticulum
3D system of sheet-like membranes spread throughout the cytoplasm
Continuous with outer membrane of nucleus
Membranes enclose a network of tubules and flattened sacs called cisternae
What is the function of the Rough Endoplasmic Reticulum?
Provide a large surface area for the synthesis of proteins and glycoproteins
Provide a pathway for transport of proteins throughout the cell
Describe the difference in structure between the rough Endoplasmic Reticulum and the smooth Endoplasmic reticulum
RER has ribosomes on the outer surface of membranes and SER lacks ribosomes on its surface and is often more tubular in appearance.
What is the function of the Smooth Endoplasmic Reticulum?
Synthesis, store and transport of lipids and carbohydrates
Describe the structure of a ribosome
Small cytoplasmic granules found in all cells, either in cytoplasm or in RER
What are the 2 types of ribosomes and what are the differences between the 2?
80s- found in eukaryotic cells
70s- found in prokaryotic cells & mitochondria. Also slightly smaller
Describe the structure of the Golgi Apparatus
Similar to SER but more compact
Stacks of membranes that make up flattened sacs called cisternae, with small rounded hollow structures called vesicles
What happens in the Golgi Apparatus
Proteins and lipids produced in ER are modified in the Golgi and then transported to the vesicles where they are regularly pinched off the ends of the cisternae.
These vesicles move to the cell surface, fuse with the membrane and release their content outside the cell
(PACKAGING AND PROCESSING)
What are the functions of the Golgi Apparatus
Add carbohydrates to proteins to form glycoproteins
Form lysosomes
Produce secretory enzymes
Secrete carbohydrates
Transport, modify and store lipids
What are lysosomes
Formed when vesicles produced by Golgi Apparatus contain enzymes
They isolate enzymes from the rest of the cell before releasing them outside the cell or into phagocytise vesicles within the cell
What are the functions of the lysosomes
Hydrolyse material ingested by phagocytic cells
Exocytosis
Digest worn out organelles
Completely break down cells after they die (autolysis)
What is the function of the chloroplast
Site of photosynthesis
Describe the structure and function of the chloroplast envelope
Double plasma membrane
Highly selective in what leaves and enters
Describe the structure and function of the Grana
Structure: stacks of 100 disc-like structures called thylakoids
Function: location of first stage of photosynthesis - absorbs light
What are thylakoids?
Contain photosynthetic pigment - chlorophyll
Some have tubular extensions (lamella) which join ajecent grana.
Describe the structure and function of the Stroma
Structure: fluid filled matrix, within it are other structures such as Starch grains
Function: location of the seconds stage of photosynthesis (synthesis of sugars)
How is the chloroplast adapted?
Granal membranes provide large surface area for attachment of chlorophyll, electron carriers and enzymes required in the first stage of photosynthesis
Fluid in the stroma possesses all the enzymes need to make sugars in the 2nd stage
Chloroplasts contain both DNA and ribosomes to manufacture proteins for photosynthesis
What is the function of the cell wall
Provided mechanical strength to prevent cell from bursting due to pressure created by osmosis
Allows water to move throughout the cell
What is the function of the vacuole
Temporary food store
Support for plants by making them turgid
Describe the structure and function of circular DNA
Structure: DNA is free in the cytoplasm
Function: Possess the genetic information for the replication of bacterial cells
Describe the structure and function of plasmids
Structure: smaller pieces of DNA that can reproduce independently
Function: possess genes that may aid in the survival of bacteria in adverse conditions, can be used as vectors between bacteria
Which ribosomes are present in prokaryotic cells?
70s (slightly smaller)
What is the function of the flagella
Rotates to move the cell
Describe the structure and function of the cell wall of a prokaryotic cell
Made up of MUREIN
Functions to give strength and structure, protects against mechanical damage and osmotic lysis
Describe the structure & function of the capsule
Structure: A layer of slime around the cell wall
Function: Protects the bacterium from other cells and helps groups of bacteria stick together for further protection
What are the features of an optical (light) microscope
Optical uses beam of light to produce an image
Magnifies up to x2000
Lower resolution
Cheap & easy to use
Creates only 2D images
What are the features of an electron microscope
Uses beam of electrons focused by electromagnets to produce an image
Magnifies up to x2,000,000
Higher resolution
Extremely expensive and more difficult to keep
Creates both 2D and 3D images
Why does an optical (light) microscope have a lower resolution than an electron microscope
Wavelength of light is a lot longer
Can only distinguish between 2 objects if they are 0.2 μm or further apart
Why does an electron microscope have a higher resolution than an optical microscope
Electron beam has a very short wavelength
Can distinguish between two objects only 0.1 nm apart
Why must a near vacuum be created within the chamber of an electron microscope
Electrons are absorbed and deflected by the molecules in the air
What are the 2 types of electron microscope
Transmission and scanning
How does a transmission electron microscope work?
Consists of an electron gun - produces beam of electrons - focused onto specimen by a condenser electromagnet
Beam passes through thin sections of specimen
Denser parts absorb more electrons and appear darker
Image is produced on a screen and can be photographed to give a photomicrograph
What are the limitations of both a scanning and transmission electron microscope ?
Resolution of 0.1 nm cannot always be achieved due difficulties in preparing specimen
High energy electron became stronger required - may destroy specimen
Complex staining process
No colour images
Whole system must be in vacuum- living organisms can’t be observed
Images can contain artefacts
What is one difference in limitations between a scanning and transmission microscope
Specimen don’t have to be extremely thin in a scanning microscope as electrons don’t penetrate as beam of electrons are directed from above not below
Scanning can also produce 3D images unlike transmission
What are the disadvantages of a scanning microscope
Lower resolution
No view of internal structures
What two things do you use to measure specimens under a microscope?
Eye piece graticule & stage micrometer graticule
What is the equation for calculating length of internal organelles using scale bar
Image length of organelle
———————————— x actual length of scale bar
Image length of scale bar
What is cell fractionation
Process where cells are broken up and the different organelles are separated out
What is the order of pellets produced by the centrifuge in cell fractionation
Pellet 1: nucleus
Pellet 2: chloroplasts
Pellet 3: mitochondria
Pellet 4: Endoplasmic reticulum and lysosomes
Last pellet: ribosomes
Step by step of cell fractionation
Tissue we are extracting is placed into ice cold, isotonic and buffered solution
The cells are broken up by a homogeniser which releases the organelles - resulting fluid is the homogenate
Homogenate is then filtered to remove any complete cells or debris
Homogenate is then placed in test tube and spun in centrifuge. (ultracentrifugation)
It starts off being spun at low speeds to compress the heaviest organelles into a pellet at the bottom
The remaining fluid (supernatant) is then transferred to another test tube and spun in the centrifuge at a faster speed to compress the next heaviest organelles into a pellet at the bottom
What are the three stages of the cell cycle?
Interphase
Nuclear division (meiosis or mitosis)
Cytokinesis
What is the order of the phases in mitosis
Interphase
Prophase
Metaphase
Anaphase
Telophase
(Cytokinesis)
What is the importance of mitosis ?
Growth, Repair and Reproduction
Describe the interphase
Period before mitosis where the cell is not dividing and chromosomes are not visible.
The cellular activity that does take place, is…
DNA replication & the replication of organelles
Describe the structure of a chromosome after replication
2 chromatids held together by a centromere.
One short arm and one long arm
Describe the prophase
Chromosomes condense (shorten and thicken) to become visible
Nuclear envelope disintegrates and the nucleolus disappears.
Centrioles move to the poles and from them spindle fibres develop
What are spindle fibres collectively known as?
Spindle apparatus
Describe the metaphase
Spindle fibres form
Spindle fibres attaches the centromeres of chromosomes
Chromosomes line up at the equator by being pulled along the spindle apparatus
Describe the anaphase
Centromeres split
Chromatids are pulled by spindle fibres to opposite poles
Energy for this process is provided by mitochondria that gather around spindle fibres
Describe the telophase
Nuclear envelope reforms around the chromosomes at the poles
Nucleolus reforms
Spindle fibres disintegrate
Chromosomes are no longer visible
Describe cytokinesis
The cytoplasm divides to form two cells with genetically identical nuclei (mitosis)
What is binary fission
Asexual reproduction of a single celled organism such as bacteria
(Prokaryotes divide this way)
Describe the stages of binary fission
Circular dna replicates - both copies attach to cell membrane at opposite ends of the cell
Plasmids replicate
Cell membrane grows between dna and pinches inwards dividing the cytoplasm
New cell wall forms, dividing the original cell into 2 identical daughter cells
Each has a single copy of circular DNA and a variable number of plasmid copies
What is cancer
A group of diseases caused by the growth disorder of cells
What are the 2 types of tumour? How does a tumour become cancerous?
Benign and Malignant
A tumour becomes cancerous if it changes from benign to malignant
How can the rate of mitosis be affected
The environment of the cell and growth factors
What causes uncontrolled mitosis
A mutation to one of the genes
Mutant cells formed are usually structurally and functionally different from normal cells.
They are capable of dividing to form tumours
How can treatment of cancer affect cancerous cells?
Preventing dna from replicating
Inhibiting metaphase in mitosis by interfering with spindle formation
What are the effects of chemotherapy on normal cells
Normal cells that also divide rapidly can be vulnerable to same damage such as hair producing cells
How can you identify cancerous cells
Large variably shaped nuclei
Many dividing cells, disorganised arrangement
Variation in shape and size
Loss of normal features
How do you calculate mitotic index
(Number of cells with condensed chromosomes ÷ total number of cells) x 100
What can the mitotic index measure or help us predict
An elevated mitotic index indicates that more cells are dividing. This knowledge can be important in predicting survival and response to chemotherapy and cancer types
What’s the name of a membrane that’s around all types of cells
Plasma membranes
Why are phospholipids an important structure to cell membranes
form a phospholipid bilayer
-allows lipid-soluble substances to enter and leave the cell
-prevent water soluble substances entering and leaving
-make membrane flexible and self-sealing
What forms do proteins come in in the cell membrane
Protein channels - form water filled tubes to allow water-soluble ions to diffuse across
Carrier proteins - bind to molecules or ions (eg: glucose and amino acids) and change shape to move these across the membrane