Cells Flashcards
The nucleus, the mitrochondrion, endoplasmic reticulum, golgi, lysosomes, ribosomes, cell surface membrane, microvilli, centrioles, plant cells, chloroplasts, cellulose cell wall, vacuoles, bacterial cell, virus, light microscope, electron microscope, cell fractionation,
What can each cell be considered as?
Each cell can be considered as an individual metabolic compartment
What is the internal structure of a cell called?
Ultrastructure
What are the distinct features of a eukaryotic cell?
Eukaryotic cells have a distinct nucleus and have membrane bound organelles
What are the different types of eukaryotic cells?
Plants, algae, animal, protozoan, and fungi
What is the nuclear envelope?
It is a double membrane that surrounds the nucleus and is continuous with the rough endoplasmic reticulum.
What is the function of the nuclear envelope?
The nuclear envelope controls the entry and exit of substances in and out of the nucleus.
The membrane also compartmentalises the reactions that occur within it
What is the function of nuclear pores?
It allows the passage of large molecules, such as mRNA, out of the nucleus.
How many pores are there?
On average there are about 3000 pores in the nucleus, each is 40-100nm in diameter
What is the nucleoplasm?
It is the jelly like material that makes up the bulk of the nucleus
What is chromatin?
It is protein bound, linear DNA that condenses into chromosomes during nuclear division
What is the structure and function of the nucleolus?
It is a small, spherical, region of the nucleus within the nucleoplasm. It manufactures rRNA and makes ribosomes. There may be more than one nucleolus per nucleus
What are the three main roles of the nucleus?
- Acts as a control centre of the cell. The nucleus controls the production of mRNA and tRNA, therefore it controls protein synthesis of cells. It is proteins that carry out the cells functions and give the cell its characteristics
- Store the genetic material of the cell in the form of chromosomes
- Manufacture RNA and ribosomes
Describe the structure of a mitochondrion
Mitochondrion are usually rod shaped and 1-10 micrometres in length. A mitochondrion is made from: a double membrane, intermembrane space, cristae, matrix
What is the function of mitochondria?
Mitochondria is where ATP is synthesised by aerobic respiration.
What is the function of the double membrane?
The 2 membranes control the entry and exit of molecules in and out of the mitochondrion. The inner membrane is highly folded to form extensions called cristae
What is the intermembrane space -
Is the space between the inner and outer membrane
What is the structure and function of Cristae?
They are extensions of the inner membrane and could extend across the whole mitochondrion. They provide a large surface area for the attachment of enzymes like ATPsynthase and other proteins involved in aerobic respiration
What is the function of the matrix?
It contains proteins, lipids, mitochondrial DNA and ribosomes. The mitochondrial DNA and ribosomes allow the mitochondrion to make it’s own proteins, independently of the nucleus
What is the endoplasmic reticulum?
It is an elaborate 3D system of sheet like membranes that spread throughout the cytoplasm of cells. It is continuous with the outer nuclear membrane. The membranes form an enclosed network of tubes and sacks, called cristernae
What is the structure of the rough endoplasmic reticulum?
RER has ribosomes presenting on the outer surfaces of the membranes.
Which cells contains a lot of RER?
Cells which make a lot of protein (e.g. secreting extracellular enzymes or plasma B cells)
What is the function of the RER?
The RER provides: A large surface area for the synthesis of proteins and glycoproteins; and A transport pathway for molecules, especially proteins throughout the cell
The RER packages proteins into vesicles and transports them to the golgi apparatus to be modified
What is the structure of smooth endoplasmic reticulum
SER lacks ribosomes on it’s outer surface and is more tube-like in appearance
What are the two functions of SER?
- Make, store and transfer lipids (combine glycerol and fatty acids)
- Make, store and transport carbohydrates
The SER packages triglycerides and carbohydrates into vesicles and transports them to the golgi apparatus to be modified
Which cells contain the most SER?
Cells that make and store large quantities of carbohydrates (e.g. liver cells and secretory cells like in the small intestine)
What is the structure of the golgi apparatus?
Almost all eukaryotic cells have a golgi. It has a similar structure to SER, but is more compact. The golgi is made form membranes that are arranged onto flattened sacks called cisternae, these are associated with small hallow membrane bound structures called vesicles.
What are the 5 roles of he golgi apparatus?
- Modify proteins by adding carbohydrates to ake glycoproteins
- Produce enzymes to be secreted, such as those secreted by stomach and pancreas
- Secrete carbohydrates like cellulose so it can be used to make a cell wall in plant cells
- Transport, modify and sort lipids
- Form lysosomes
Which cells contain the most golgi bodies?
They package lots of molecules for export (i.e. enzyme secreting gland cells or antibody producing plasma cells)
What do lysosomes contain?
They contain hydrolytic enzymes such as protease nad lipase. They also contain lysozymes, enzymes that hydrolyse the walls of certain bacteria. Up to 50 different types of enzymes might be found in 1 lysosome
What is the structure of a lysosome?
Lysosomes are roughly 1 micrometre in diameter and are composed of a single membrane that forms a sphere
What is the functions of lysosomes?
Lysosomes isolate hydrolytic enzymes from the rest of the cell before relsing them, this is to prevent any unwanted breakdown of the cells ultrastructure.
- Hydrolyse foreign materials ingested by phagocytic cell
- Release enzymes to the outside of the cell (extracellular enzymes via exocytosis) in order to hydrolyse and breakdown molecules outside of the cell (e.g. bacterial and fungal cells breaking down dead material)
- They breakdown damaged and worn out organelles so the useful molecule they are made from can be re-used
- Completely breakdown cells after they have died (autolysis)
What is a ribosome?
Small cytoplasmic granules found in all cell. They may be found in the cytoplasm, or attached to the membrane of the RER
What are the three types of ribosomes?
- 80S/large - found in eukaryotic cells and measure 25-25nm in diameter
- 70S/smaller - found in prokaryotic cells and measure 18-20nm in diameter
- 55S ribosomes - found in mitochondria chlorooplasts
What is the endosymbiont theory
Mitochondria and chloroplasts evolved before bacteria and other prokaryotes and that at some point, they developed a symbiotic relationship with the ancestor of a eukaryotic cell
What is the cell surface membrane’s function?
It controls the passage of molecules in and out of cell
What is the structure of the cell surface membrane?
It is made up of phospholipids, specific transport proteins and carbohydrates arranged into what is described as a fluid mosaic model
What are microvilli?
They are finger like projections of the cell surface membrane, which greatly increases the surface area of the cell membrane. This increases the efficiency of which digested food is absorbed. They are found on epithelial cells in the ileum
What is the centrioles function?
In mitosis centrioles produce a network of spindle fibres across the cell onto which the chromosomes attach. These spindle fibres get shorter and pull the chromatids apart during mitosis. These organelles are not found in plant cells
What is the size of a chloroplast?
They vary in shape and size but generally, they are disc shaped and are 2-10 micrometres long and are about 1 micrometer in diameter
What are the main features of chloroplast?
. The chloroplast envelope
. The grana
. The stroma
Describe the chloroplast envelope (structure & function)
It is a double plasma membrane that surrounds the organelle. It is highly selective and controls what enters and exits the chloroplast
Describe the grana (Hint: thylakoid structure and function)
They are stacks of up to 100 disc like structures called thylakoids. These thylakoids are made from plasma membrane. Within the membrane is the photsynthetic pigment called chlorophyll. Some thylakoids have tubular extensions that link them to other grana. The thylakoid membrane is where the first stage of photosynthesis takes place
Describe the stroma (structure & function)
It is a fluid filled matrix which possess all the enzymes required for the second stage of photosynthesis to occur. Within the stroma there are other structures, such as starch grains (Amyloplasts)
Why can chloroplasts make their own proteins and enzymes fro photosynthesis?
Chloroplasts contain their own DNA and their own ribosomes so can make proteins independent of the nucleus
What are the structures of a cell wall
. The wall consists of microfibrils of cellulose, embedded in a matrix. The microfibrils contribute to the overall strength of the cell wall.
. They consist of a number of polysaccharides
. There is a thin layer, middle lamella, which marks the boundary between tewo plant cells, and cements two adjacent cells together
. There are gaps between the cell walls and the middle lamella, that allows the cytoplasm of the two cells to be linked and allow them to exchange substances
What is the function of the cell wall?
. Provides mechanical strength to prevent the cell from busting under pressure created by osmosis
. Provides mechanical strength to the plant as a whole
. Allows water to pass along it and so contribute to the movement of water through the plant as a whole
What is a vacuole?
A fluid filled sack bound by a single membrane called the tonolpast. In mature plants there is large, permanent vacuole that contains a solution of mineral salts, sugars, amino acids, waste and sometimes pigments
What purposes can vacuoles serve?
. Support herbaceous plants, making tells turgid
. Sugars and amino acids stored could act as a temporary food source
. The pigments may colour petals and attract pollinating insects
Why are cells specialised?
To carry out certain roles
What are similar cells group into?
Tissue
What are similar tissues grouped into?
Organs
What can organs be group into?
Organ systems
How is it that cells become specialised?
They turn on certain genes and turn off others
What do prokaryotes not contain?
They do not have a nuclei or other membrane bound organelles
Describe the DNA in prokaryotes
It is circular and not associated with histones, it is also free in the cytoplasm
Describe the DNA in eukaryotes
It is linear and associated with histones, it is found within a nuclear envelope (nucleus)
What ribosomes do prokaryotes contain?
70S
What ribosomes do prokaryotes contain?
80S
How do prokaryotes synthesise ATP?
Mesosomes
How do eukaryotes synthesise ATP?
Mitochondria
What is the cell walls in prokaryotes made of?
Murein/Peptidogyclan
What is the cells walls in eukaryotes (plant cells) made of?
Cellulose
Which domains have capsules?
Prokaryotic - some have capsule, one or more flagella, one or more plasmids
What do virus’ contain?
. DNA or RNA, which can be single or double stranded
. Enzymes to replicate it’s genetic information and insert it into the host cell DNA
What surrounds the DNA/RNA?
. A protein coat (capsid)
. Attachment proteins which enable it to bind to its’s host cell
How can you tell which microscope is being used?
SEM microscopes produce 3D images, TEM microscopes have higher resolution images than light microscopes at high magnifications
How are each microscopes illuminated?
Light microscopes - light
Electon microscopes - beam of electrons
How are each microscopes focused?
Light -lenses
Electron microscopes - electomagnets
What is the maximum magnification of each microscope?
Light - x1,500
Electron microscopes - x500,000
What is the resolution of each microscope?
Light - 200nm
Electron microscope - 1nm
How are the specimens used in each microscope?
Light - living/dead
Electron microscope - dead
How would you describe the staining process for each microscope?
Light - easy
Electron microscope - complex
What is the first step in fractionation?
. Homogenise the tissue in a blender in an ice-cold, isotonic, buffered solution
. Ice-cold - reduces the action of enzymes that would damage the organeels
. Isotonic - prevents osmosis so the organelles don’t burst or shrivel
. Buffered - stops pH changes which could denature proteins
What is the second step in fractionation?
The mixture is filtered to remove any large pieces of tissue/cell wall producing a supernatant (a solution of suspended organelles)
What is the third step in fractionation?
Differential centrifugation is carried out on the supernatant. The densest organelles are forced to the bottom of the tube into a pellet. The pellet is removed. (The nucleus is the densest so is found in the first pellet)
What is the fourth step in fractionation?
The supernatant is centrifuged at a higher speed for a longer time so less dense organelles are forced to the bottom of the tube into a pellet. (The mitochondria is the second densest so is found in the second pellet, the last pellet removed will contain the least dense organelles the ribosomes)
