Topic 2 - Cells Flashcards
What is the function of the nucleus?
- site of DNA replication and transcription.
- Contains the genetic material of the cell.
What is the structure of the nucleus?
- nuclear envelope: double membrane
- Nuclear pores
- nucleoplasm: granular jelly like material
- Chromosomes: protein bound linear DNA.
- nucleolus: smallest fear inside which is the site of RNA production and makes ribosomes.
What is the function smooth endoplasmic reticulum?
Synthesis and store lipids and carbohydrates.
What is the structure of the smooth endoplasmic reticulum?
Folded membranes called cisternae
What is the function of the rough endoplasmic reticulum?
Protein synthesis
What is the structure of the rough endoplasmic reticulum?
Folded membranes called cisternae and has ribosomes on the surface.
What is the structure of the Golgi apparatus?
Folded membranes making cisternae and secretary vehicles pinched off from the cisternae.
What is the function of the Golgi apparatus?
- add carbohydrates to proteins to form glycoproteins.
- Form lysosomes
- produce enzymes.
What is the structure of lysosomes?
Bags of digestive enzymes
What is the function of a lysosome?
- hydrolyse phagocitic cells
- exocytosis: release enzymes to outside
What is this function of the mitochondria?
- sight of aerobic respiration
- Site of ATP production.
What is the structure of the mitochondria?
- double membrane
- Inner membrane called the cristae.
- Fluid centre called the mitochondrial matrix
- Loop of mitochondria DNA
What is the function of the ribosome?
The site of protein synthesis
What is the structure of a ribosome?
- small made up of two sub units of protein and RNA
- 80s large ribosomes found in eukaryotic cells.
- 70s small ribosomes found in prokaryotic cells, mitochondria and chloroplasts.
What is the function of the vacuole?
- makes cells turgid and therefore provide support.
- Temporary store of sugars and amino acids.
- The pigment may colour petal to attract pollinators.
What is the structure of the vacuole?
Filled with fluids surrounded by a single membrane called a tonoplast.
What is the structure of the chloroplast?
- surrounded by a double membrane
- Contains thyakoids (folded membranes embedded with pigment)
- Fluid filled stroma contains enzymes for photosynthesis.
- Found in plants
What is the function of the chloroplast?
- Sight of photosynthesis
What is the structure of the cell wall?
Plants – made of cellulose
Fungi – made of chitin
What are the key differences between prokaryotic and eukaryotic cells?
- The cells are much smaller in prokaryotic cells
- No membrane bound organelles
- Smaller ribosomes
- No nucleus
- A cell wall made of murein
What are the features of a virus?
- viruses are a cellular and nonliving
- The structure of virus particles consist of genetic material, capsid and attachment proteins
- Viruses replicate inside of cells making it difficult to destroy them without harming the host cell
Define magnification
How many times larger the image is compared to the object.
Define resolution.
The minimum distance between two objects in which they can still be seen as separate.
What is the optical microscope?
- A beam of light is condensed to create an image
- poor resolution due to light having a longer wavelength.
- Lower magnification
- Colour images
- Can view living samples
What is an electron microscope?
- A beam of electrons is condensed to create the image. Electromagnets are used to condense the beam.
- Higher resolving power as electrons have a short wavelength.
- Black and white images
- Sample must be in a vacuum and therefore nonliving.
What is a disadvantage of an optical microscope?
Light microscopes have a poor resolution due to the long wavelength of light. Small organelles in a cell are not visible using an optical microscope.
What is a positive of the optical microscope?
Can view living samples and can be examined and a colour image as obtained.
What are the negatives of an electron microscope?
- samples must be in a vacuum so they cannot be living
- The image is black-and-white
- The sample must be complexly stained.
- creates a 2-D image
What is the transmission electron microscope?
Extremely thin specimens are stained and placed in a vacuum. An electron gun produces a beam of electrons that passes through the specimen. some parts absorb the electrons and appear dark. The image produced is 2-D and shows detailed images on the internal structure of the cell.
What is a scanning electron microscope?
The specimens do not need to be thin as the electrons are not transmitting through. Instead electrons are beamed onto the surface and the electrons are scattered in different ways depending on the contours. This produces a 3-D image.
What is the calculation for magnification?
Image size = actual size x magnification
What is cell fractionation used for?
- to isolate different organelles so they can be studied
- This enables individual organelle structures and functions to be studied.
What are the steps to cell fractionation?
- homogenisation: cells are broken to release the contents and organelles are then separated. The sales must be prepared in a cold, isotonic and buffered solution.
-ultracentrifugation: put a sample in the centrifuge and spin at different speeds, separating the organelles according to their densities.
Why does the cell have to be prepared in a cold, isotonic and buffered solution?
– Cold: to reduce enzyme activity. When the cell breaks open enzymes are released, which could damage the organelles.
– Buffered: the solution has a pH buffer to prevent damage to organelles.
– Isotonic: must be the same water potential to prevent osmosis as this could cause the organelles to shrivel or burst.
Differential centrifugation
– The centrifuge spins and the centrifugal forces causes pellets of the most dense organelles to form at the bottom.
- The centrifuge is first spun at a low speed and the process is repeated at increasing fast speeds
– Each time the supernatant is removed, leaving behind a pellet of organelles
– The supernatural is spun again to remove the next pellet organelles.
What is the order of densities in ultracentrifugation?
Nuclei, chloroplasts, mitochondria, lysosomes, endoplasmic reticulum and ribosomes
How did the different cells divide?
– Eukaryotic: cells enter the cell cycle and divide by mitosis or meiosis.
– Prokaryotic: binary fission
– Viruses: replicate inside of the wholesale they invade by injecting the nucleic acid into the cell to replicate the virus particles.
What are the cell cycle stages?
Interphase, nuclear division and cytokinesis.
In terms of the cell cycle, what is interphase?
The longest stage in the cell cycle. Interphase is when the organelles double, the cells grow and then DNA replicates.
What is the nuclear division in terms of the cell cycle?
Can be either mitosis creating two identical diploid cells; or meiosis creating genetically different haploid cells. Mitosis creates cells with identical DNA for growth and repair, whereas meiosis create gametes.
What is cytokinesis in terms of cell cycle?
The final stage it is the division of the cytoplasm to create two cells.
What happens during prophase of mitosis?
Chromosomes condensed and become visible.
What happens during metaphase?
Chromosomes align along the equator of the cell. The spindle fibres released from the polls now attached to the centromeres and chromatid.
What happens during anaphase?
Spinal fibres retract and pull the centromeres and chromatids to opposite poles. Causing the Centromere to divide into pulling apart the chromatids.
What happens in telophase ?
Chromosomes become long and thinner spindle fibres, disintegrate, and nucleus starts to reform.
Cytoplasm splits into to create the two genetically identical cells.
How can you calculate the mitotic index?
Mitotic index = the number of cells in mitosis/the number of cells x 100.
Explain the process of binary fission.
- Replication of circular DNA and of plasmids.
- Division of the cytoplasm to produce two cells each with a single copy of the circular DNA and a variable number of plasmids.
What is the plasma membrane?
- Fluid-mosaic model: due to the mixture and movement of the phospholipids proteins, glycoproteins and glycolipids.
- All of these molecules arranged within the phospholipid bilayer create the partially permeable membrane that is the cell surface membrane.
What are protein channels?
Form tubes that will fill with water to enable water soluble ions to diffuse.
What is the role of the carrier proteins?
They bind with others and larger molecules such as glucose and amino acid and change shape to transport them to the other side of the membrane.
What is the definition of simple diffusion?
The net movement of molecules from a high area of concentration to an area of lower concentration until equilibrium is reached and it does not require ATP.
What is facilitated diffusion?
Passive process, but proteins are used to transport molecules. The movement of ions and polar molecules which cannot simply diffuse can be transported across membranes by facilitated diffusion using protein channels and carrier proteins.
What is osmosis?
Osmosis is the movement of water from an area of higher water potentials to an area of lower water potential across a partially permeable membrane.
What is meant by an isotonic hypotonic and hypotonic solution?
Isotonic – the water potential is the same in the solution and the cell within the solution.
Hypotonic – the water potential of a solution is more positive than the cell.
Hypertonic – when the water potential of a solution is more negative than the cell.
What is the process of active transport?
- Transport is to carry a proteins spanning the cell membrane.
- Molecule binds to a receptor complimentary in shape on the protein.
- ATP vines to the carrier protein from the inside of the cell and is hydrolysed into ADP + Pi.
- This causes the carrier protein to change shape and release the molecule to the other side.
- The phosphate ion is then released and the protein returns to its original shape.
What is active transport?
The movement of molecules or ions into or out of a cell from a region of lower concentration to a region of higher concentration using ATP and carrier proteins.
What happens with co transport and sodium ions in the gut?
– Sodium ions are actively transported out of the epithelial cell into the blood.
– Sodium ions can then diffuse from the lumen down their concentration gradient into the epithelial cell.
– The protein sodium ions diffuse through is a co-transporter protein so either glucose or amino acids also attacked and are transported into the epithelial cell cell against the concentration gradient.
What adaptions do cells have for rapid transport?
– An increase in surface area to volume ratio
– An increase in the number of protein channels and carry a molecules in their membranes.
What do lymphocytes do?
Identify the presence of pathogens and potentially harmful non-self substances in the body to destroy them.
How do lymphocytes distinguish between pathogens and self-cells?
Each type of cell has specific antigens on its surface that identify it. These molecules are usually proteins as their tertiary structure enables lots of unique identifiable shapes to be made.
What is four things can lymph sites identify as non-self?
– toxins
– Pathogens
– Cells from other organisms
– Abnormal body cells.
What is an antigen?
A molecule usually a protein that triggers an immune response by production of antibodies when detected by the body.
What is the definition of cotransport?
The transport of two different molecules or ions across a membrane through the same protein carrier.
Any previous immunity to the pathogen through infection is no longer effective as the memory cells in the blood will have a memory of the old antigen shape.
This is known as antigens variability.
What is antigen variability?
- Pathogens DNA can mutate frequently. If a mutation occurs in the gene which codes for the antigen then the shape of the antigen will change.
- Any previous immunity is lost as the memory cells in the blood will have a memory of the old antigen shape.
What is an example of antigen variability?
The influenza virus mutate and changes its antigens very quickly and this is why a new flu vaccine has to be created each year.
What is the first line of defence in the immune response?
Chemical and physical barriers such as the skin and stomach acid.
What are the two white blood cells and what are the difference?
Phagocytes - form a non-specific response.
Lymphocytes - a specific response.
What is a phagocyte?
A macrophage that carries out phagocytosis. They are found in the blood and in tissue.
What is phagocytois used for?
Any non-self cell that is detected will trigger the same response to destroy it.
What are the stages of phagocytosis?
- Phagocytes are in the blood and tissue and any chemicals or debris released by pathogens or abnormal cells attract the phagocytes and they will move towards these cells.
- There are many receptor binding points on the surface of the phagocytes. They were attached to chemicals or antigens on the pathogen via these receptors.
- The phagocytes changes shape to move around and engulf the pathogen.
- Once the pathogen is contained within a phagosome vesicle.
- A lysosome within the phagocyte will refuse with the phagosome and release its contents.
- The lysosome enzyme is released into the phagosome. This is a lytic enzyme which hydrolyses the pathogen.
- This destroys the pathogen.
- The soluble products are absorbed and used by the phagocyte.
What is a T lymphocyte?
– Lymphocytes are white blood cells involved in the specific immune response.
– All lymphocytes are made in the bone marrow but t cells mature in the thymus.
– The cell mediated response is the response involving t cells and body cells.
Why is the cell mediated response specific?
Because T cells respond to the antigens on the surface of cells.
What are antigen presenting cells?
Any cell that presents a non-self antigen on their surface: infected body cells will present the viral antigens on their surface.
A macrophage which has engulfed and destroyed a pathogen will present the antigens on their surface.
Cells of a transplanted organ will have different shaped antigens on their surface compared to your self-cell antigens.
Cancer cells will have an abnormal shape compared to self -cell antigens.
What is the cell mediated response?
- Once a pathogen has been engulfed and destroyed by a phagocyte, the antigens are positioned on the cell surface. This is now called an antigen presenting cell.
- Helper T cells have receptors on their surface which can attach the antigens on antigen presenting cells.
- Once attached this activates the helper T cells to divide by mitosis to replicate and make large numbers of clones.
- Cloned helper T cells differentiate into different cells.
What do cloned help T cells differentiate into at the end of the cell mediated response?
– Some remain as helper T cells and activate B lymphocytes.
– Some simulate macrophages to perform more phagocytosis.
– Become memory cells for that shaped antigen.
– Some become cytotoxic T cells.
What does cytotoxic T cells do?
They destroy abnormal or infected cells.
They release a protein called perforin which embeds in the cell surface membrane and makes a pore so that any substances can enter or leave for cell.
What is a B lymphocyte?
– Lymphocytes are white blood cells involved in the specific immune response.
– All lymphocytes are made in the bone marrow and B cells mature there too.
– The humoral response is the response involving B cells and antibodies. Antibodies are soluble and transport in bodily fluids. (Humour) is an old term for bodily fluids hence the name humoral response.
How do B cells become activated?
– There are approximately 10 million different B cells which have antibodies on their surface complementary to 10,000,000 different antigens.
– Antigens in the blood collide with their complementary antibody on a B cell. The B cell takes in the antigen by endocytosis and then presents it on its cell surface membrane.
– When the B cell collides with a helper T cell receptor this activates the cell to go through clonal expansion and differentiation.
– B cells undergo mitosis to make large numbers of cells these differentiate into plasma cells or memory B cells.
– Plasma cells make antibodies.
– B. Memory cells can divide rapidly into plasma cells, when reinfected with the same pathogen to make large numbers of antibodies rapidly.
What are memory B cells?
Memory B cells can live for decades in your body, whereas plasma cells are short-lived.
Do not make antibodies rather they will divide by mitosis and make plasma cells rapidly if they collide with an antigen they have previously encountered.
This results in large numbers of antibodies being produced so rapidly that the pathogen is destroyed before any symptoms can occur.
What are antibodies?
– They have a quaternary structure (4 polypeptide chains).
– They have a variable region which is the part of the antibody that binds to the antigen.
– They have a constant region
What is antibodies agglutination?
Antibodies are flexible and combined to multiple antigens to clump them together.
This makes it easier for phagocytes to locate and destroy the pathogens.
What is passive immunity?
– Antibodies are introduced into the body.
– The pathogen doesn’t enter the body so plasma cells and memory cells are not made.
– No long-term immunity.
What is active immunity?
– Immunity created by your own immune system following exposure to the pathogen or its antigen.
– natural, active immunity: following infection and the creation of the bodies, own antibodies and memory cells.
– artificial active immunity: following the introduction of a weak version of the pathogen or antigens via a vaccine.
How do vaccines work?
– Small amounts of weekend or dead pathogen or antigens are introduced in the mouth or by injection.
– Exposure to the antigens activates the cell to go through clonal expansion and differentiation.
– B cells undergo mitosis to make large numbers of cells these differentiate into plasma cells or memory B cells.
– Plasma cells make antibodies.
– B Memory cells can divide rapidly into plasma cells when reinfected with the same pathogen to make large numbers of antibodies rapidly.
What is herd immunity?
If enough of the population of vaccinated, the pathogen cannot spread easily amongst the population. This provides protection for those who are not vaccinated.
What is the structure of HIV?
Core = genetic material (RNA) and the enzyme reverse transcriptase, which are needed for viral replication.
Capsid = outer protein coat.
Envelope = extra outer layer made out of membrane taken from the host cell membrane.
Protein attachments = on the exterior of the envelope to enable the virus to attach to the host helper T cell.
How does HIV replicate in helper T cells?
– HIV is transported around in the blood until it attaches to a CD4 for protein on the helper T cell.
– The HIV protein capsule then fuses with the helper t cell membrane, enabling that RNA and enzyme from HIV to enter.
– The HIV enzyme reverse transcript copies the viral RNA into a DNA copy moves to the cell nucleus. This is why it is called a retrovirus.
– Here mRNA is transcribed and the helper T cell starts to create viral proteins to make new viral particles.
Why is HIV eventually fatal?
With the help of T cells being destroyed by the virus the host cell is unable to produce an adequate immune response to other pathogens and its left vulnerable to infections and cancer.
What are monoclonal antibodies?
– A monoclonal antibody is a single type of antibody that can be isolated and cloned.
– Antibodies are proteins which have binding sites complementary in shape to certain antigens.
What can monoclonal antibodies be used for?
– Medical treatment.
– Medical diagnosis.
– Pregnancy test.
What is direct monoclonal antibody therapy?
Some cancer can be treated using monoclonal antibodies which are assigned with a binding site complimentary in shape to the antigens on the outside of of cancer cells.
The antibodies are given to the cancer patient and attached the cancer cells. Well, the antibodies are bound to the cancer antigens this prevents chemicals binding to the cancer cells which enable uncontrolled cell division.
Therefore, the monoclonal antibodies prevent the cancer cells growing, and as they are designed to only attach the cancer cells they do not cause harm to other normal cells.
What is indirect monoclonal antibody therapy?
Cancer can also be treated with monoclonal antibodies complementary in shape to the antigens on the outside of the cancer cells which have drugs attached to them.
This cancer drug is therefore delivered directly to the cancer cells and kill them. This reduces the harmful side effects that traditional chemotherapy and radiotherapy can produce.
This is often referred to as ‘bullet drugs’.
What is the ELISA test?
There is use of two antibodies:
– first mobile antibody complimentary to the antigen being tested for and has a coloured dye attached.
– A second antibody complimentary in shape to the antigen is immobilised in the test.
– a third antibody is immobilised and is complimentary in shape the first antibody.
What is the ethical issues with monoclonal antibodies?
Creating monoclonal antibodies requires mice to produce the antibodies and tumour cells which lead to ethical debate as to whether this use of animals is justified to enable the better treatment of cancers in humans and detect disease.
