C1 - Cells and Microscopy Flashcards
What’s a multicellular organism made up of?
Hundreds - Billions of cells
Each type of cell has a specific internal structure which makes it efficient for its role.
What is compartmentalisation?
When the internal structure of a cell is/can be divided up into areas specialised for specific functions.
What is a leucocyte?
A white blood cell - they are eukaryotic cells, meaning they possess a distinct nucleus and membrane-bound organelles.
How can the structure of organelles be studied?
By using an electron microscope.
What is an eukaryotic cell?
A cell that has a true nucleus (contained by a nuclear envelope) which contains membrane-bound organelles in the cytosol such as the Golgi apparatus.
How are eukaryotic cells membrane-bound?
All organelles within an animal cell are contained by the cell surface membrane.
What is the nucleus of a cell and what does it contain?
The most important structure of a eukaryotic cell.
It’s a large, spherical organelle 10-20 um in diameter surrounded by a double membrane, the nuclear envelope.
It contains genetic, hereditary material DNA and controls the cell’s activities.
What is the nuclear envelope and what does it do?
A (porous) membrane surrounding the nucleus.
It controls the entry and exit of materials to and from the nucleus.
There are typically 3000 pores which allow the passage of large molecules out of the nucleus e.g. messenger RNA (mRNA).
Why does the nuclear envelope have pores?
To allow the passage of large molecules out of the nucleus.
What is the liquid within the nucleus?
What does it contain?
Nucleoplasm - it contains the chromatin (DNA) and the nucleolus (a small spherical structure that produces ribosomal RNA (rRNA) and assembles the ribosomes)
What is nucleoplasm?
The liquid in the nucleus which contains chromatin (DNA) and the nucleolus.
What’s the nucleolus?
A small spherical structure that produces ribosomal RNA (rRNA) and assembles the ribosomes.
Its main function is to rewrite ribosomal RNA (rRNA) and combine it with proteins. This results in the formation of incomplete ribosomes.
What is the function of the nucleus?
To control the activities of the cell via the production of mRNA
To contain the genetic material in the form of DNA coiled around proteins to form linear chromosomes
To manufacture rRNA and ribosomes
What are cristae?
Folds in the inner membrane of mitochondria
They increase the surface area
What are mitochondria?
Rod-shaped organelles (between 1-10um in length).
They are surrounded by the mitochondrial envelope - (the outer membrane controls materials entering and exiting the mitochondrion and the inner membrane is folded to form the cristae)
What is the purpose of cristae?
To provide a larger surface area for enzymes involved in the synthesis of ATP to be attached to.
What is the matrix?
The liquid inside the cristae (the matrix) which contains proteins (including enzymes for the breakdown of carbohydrates), lipids and small amounts of circular DNA.
The substance between cells or in which structures are embedded
What’s the function of the mitochondria?
To carry out the later stages of aerobic respiration.
To produce ATP, an energy transfer molecule.
What is the endoplasmic reticulum?
The ER is a series of flattened membrane-bound tubules that spread through the cytoplasm.
The membrane bound sacs are called cisternae.
It comes in two types: SER and RER
“A network of membranous tubules within the cytoplasm of a eukaryotic cell, continuous with the nuclear membrane. It usually has ribosomes attached and is involved in protein and lipid synthesis.”
What are cisternae?
A fluid-containing sac or cavity in the body of an organism. / One of the saclike vesicles that comprise the endoplasmic reticulum.
The ER consists of a network of membrane lamellae and tubules called cisternae; the internal space of the ER is called the cisternal space or the lumen.
What is smooth endoplasmic reticulum?
What’s its function?
SER is cisternae that are often tubular in appearance.
It’s function is to synthesis, store and transport lipids and carbohydrates.
What is rough endoplasmic reticulum?
What’s its function?
RER is cisternae which has ribosomes attached to its outer surfaces.
It is continuous with the outer nuclear membrane.
It’s function is to provide a large surface area for protein and glycoprotein synthesis and to provide a pathway for transporting proteins and other materials through the cell.
It makes proteins for the membrane or for outside the cell transported by blood (meanwhile ordinary/free ribosomes make protein for the inside of the cell)
Are ribosomes organelles?
Ribosomes are not organelles.
They are not membrane-enclosed, instead they are macromolecules made of both RNA and proteins.
If you ever have trouble remembering, just recall that there are ribosomes found in bacteria even though bacteria do not contain organelles.
What are ribosomes?
They are NOT membrane bound organelles - they are cytoplasmic granules made from rRNA and protein.
They’re found free in the cytoplasm or with the rough ER.
What is the role of ribosomes?
To join amino acids in a specific order, the order of which is dictated by messenger RNA (mRNA) molecules.
The small ribosomal subunit reads the RNA and the large subunit joins amino acids together to form polypeptide chains.
How are proteins made?
Messenger RNA (mRNA)
Ribosomes are the site of protein synthesis.
They are found in the cytoplasm but DNA is found in the nucleus.
The genetic code needed to make a particular protein is carried from the DNA to the ribosomes by a molecule called mRNA.
Making:
mRNA from DNA is called transcription
Proteins from mRNA is called translation
What are Svedberg units of measure?
How does it relate to ribosomes?
A measure of the sedimentation rate of particles e.g. Rate for the substance to reach the bottom of a tube in centrifuge. (Unit S)
Ribosomes in eukaryotic cells are 80S 20-30nm in diameter with a ratio of 1:1 (rRNA:proteins)
Each consists of a small 40S subunit and a large 60S subunit
What’s the Golgi apparatus?
Similar to the smooth ER in appearance, it is made from a stack of membrane bound sacs (cisternae) and small, hollow, spherical vesicles.
(Typically 40-100 stacks (3-6 cisternae per pack)).
What takes place within the Golgi apparatus?
Proteins and lipids made in the ER are passed to the Golgi apparatus by the addition of non-protein portions
(e.g. Oligosaccharides or glycans to form a glycoprotein or by the addition of phosphates)
The Golgi apparatus labels the proteins to enable them to be accurately sorted and transported to their correct destinations.
After modification, the proteins and lipids are packed into vesicles which bud off from the ends of the Golgi apparatus for transport around the cell.
What happens to the proteins and lipids produced in the endoplasmic reticulum?
They’re transported to the Golgi apparatus via vesicles which then receives the proteins and lipids.
It then sends them to where they’re needed via more vesicles and go to the cell membrane where the proteins make a channel so large molecules can lass through and enter the blood.
What are the functions of the Golgi apparatus?
To assemble polypeptides into proteins
To pack proteins and carbohydrates into vesicles for secretion by exocytosis
What’s exocytosis?
Exocytosis describes the process of vesicles fusing with the plasma membrane and releasing their contents to the outside of the cell.
(E.g. Secretion)
What’s endocytosis?
Endocytosis is the process of capturing a substance or particle from outside the cell by engulfing it with the cell membrane, and bringing it into the cell.
(E.g. Uptake)
What are vesicles?
What do they do?
Small, fluid containing, membrane-bound organelles.
They’re used in processes like secretion (exocytosis), uptake (endocytosis) and transport of minerals in the cytoplasm.
They’re also involved in transport within the cell, cell metabolism and enzyme storage.
What’s phagocytosis?
A type of endocytosis
The ingestion of bacteria or other material by phagocytes and amoeboid protozoans.
What are lysosomes?
Spherical membrane-bound vesicles (sacs) that are produced by the Golgi apparatus.
They contain up to 50 different types of enzymes (usually proteases and lipases)
They’re typically 1um diameter and pH of 5
What is the function of lysosomes?
To digest unwanted materials in the cytoplasm.
They have an important role in phagocytosis where they fuse with phagocytic vesicles so the enzymes can digest engulfed pathogens.
What’s a centriole?
Each of a pair of minute cylindrical organelles near the nucleus in animal cells, involved in the development of spindle fibres in cell division.
A centriole is a small set of microtubules arranged in a specific way.
There are nine groups of microtubules.
When two centrioles are found next to each other, they are usually at right angles.
The centrioles are found in pairs and move towards the poles (opposite ends) of the nucleus when it is time for cell division.
What’s the plasma membrane?
A microscopic membrane of lipids and proteins which forms the external boundary of the cytoplasm of a cell or encloses a vacuole, and regulates the passage of molecules in and out of the cytoplasm.
The plasma membrane is the boundary between the cell and its environment.
It regulates what enters and exits the cell. Cells must maintain an appropriate amount of molecules to function inside them.
What are peroxisomes?
A small organelle present in the cytoplasm of many cells, which contains the reducing enzyme catalase and usually some oxidases.
What’s the cytoskeleton?
A microscopic network of protein filaments and tubules in the cytoplasm of many living cells, giving them shape and coherence.
The cytoskeleton is a structure that helps cells maintain their shape and internal organization, and it also provides mechanical support that enables cells to carry out essential functions like division and movement.
There is no single cytoskeletal component. Rather, several different components work together to form the cytoskeleton.
What are micro villi?
Folded plasma membranes
What’s the cytosol?
The aqueous component of the cytoplasm of a cell, within which various organelles and particles are suspended.
Cytoplasm is the cytosol and the organelles.
What are microtubules?
Hollow filaments of protein tubules which give structural support and are part of the cytoskeleton and form organelles e.g. Centrioles and cilia.
What’s the chromatin?
Granular material in the nucleoplasm.
During cell division it condenses into more tightly coiled threads called chromosomes.
What are erythrocytes?
Red blood cells (the most common type of cell)
They develop in the bone marrow and circulate within the blood for 100-120 days.
In humans, mature red blood cells are flexible and oval biconcave discs.
What is the function of erythrocytes?
To deliver oxygen from the lungs to the body.
They contain haemoglobin, an iron containing protein that can bind reversibly with oxygen to form oxyhemoglobin.
Erythrocytes (red blood cells) lack a cell nucleus and most organelles.
What does this enable them to do?
Have a large surface area to volume ratio
Become biconcave, enabling them to be flexible and squeeze through capillaries
How are erythrocytes produced?
They’re produced in bone marrow from erythropoietic stem cells in a process called erythropoiesis.
Erythropoiesis is stimulated by the hormone ‘erythropoietin’ (EPO) which is produced by the kidney
What’s erythropoiesis?
The process of the production of erythrocytes in bone marrow from erythropoietic stem cells.
What are reticulocytes?
Immature red blood cells.
They have no nucleus and can be identified in a blood smear when stained with methylene blue.
What are thrombocytes?
Platelets
They are biconvex discs of cytoplasm fragments / cell fragments surrounded by a cell surface membrane.
They’re produced in bone marrow (by megakaryocytes) and have no nucleus
On a stained blood smear, platelets appear as dark purple spots.
What is the function of thrombocytes?
To assist the clotting and clot formation of the blood to prevent bleeding.
A blood clot is also known as a thrombus.
This is done by the thrombocytes binding to the injured tissue (adhesion), changing shape, connecting together and forming a bridge.
What is thrombogenesis?
(Coagulation) is when the blood changes into a gel.