2- Cells Flashcards
What’s the structure of the nucleus
Nuclear envelope- double membrane
Nucleoplasm- jelly like
Chromosomes- protein bound linear DNA
Nucleolus- site of rRNA and ribosome production
What’s the function of the nucleus
Site of DNA replication and transcription
Contains genetic code
What’s the structure of endoplasmic reticulum
Rough and smooth both have folded membrane (cisternae)
Rough ER have ribosomes on cisternae
What’s the function of the smooth and rough endoplasmic reticulum
SER- synthesises and stores lipids and carbohydrates
RER- protein synthesis
What’s the structure of Golgi apparatus/vesicles
Folded membrane forming cisternae
Secretary vesicles pinch off from cisternae
What’s the function of Golgi apparatus/vesicles
Adds carbs to proteins forming glycoproteins
Produces secretory enzymes
Transports, modifies, stores lipids
Form lysosomes
Labels molecules with a destination
Finished products transported to cell surface in the vesicles, fuse with membrane, contents released
Structure of lysosomes
Bag of digestive enzymes
Function of lysosomes
Hydrolyse phagocytic cells
Autolysis, completely break down dead cells
Exocytosis, release enzymes outside of membrane to destroy material
Digests worn organelle for reuse of material
Structure of mitochondria
Double membrane
Inner membrane called cristae
Fluid centre called mitochondrial matrix
Loop of mitochondrial DNA
Function of mitochondria
Site of aerobic respiration and ATP production
DNA to code for enzymes needed for respiration
Structure of ribosomes
Small, two subunits of protein and rRNA
80s, larger found in eukaryotes
70s, smaller found in prokaryotes, mitochondria and chloroplasts
Function of ribosomes
Site of protein synthesis
Structure of vacuoles (plant cell)
Fluid surrounded by a single membrane called tonoplast
Function of vacuole (plants)
Turgid,support
Temporary store of sugars and amino acids
Pigments colour petals attracting pollinators
Structure of chloroplasts (plants)
Double membrane
Contains thylakoids (folded membranes with pigments)
Fluid filled stroma contains enzymes for photosynthesis
Function of chloroplasts (plants)
Site of photosynthesis
Structure of a cell wall (plants and fungi)
Plants- microfibrils of a polymer of cellulose
Fungi- chitin, a polysaccharide containing nitrogen
Function of a cell wall
Structural strength to the cell
Structure of the cell surface/plasma membrane
Phospholipid bilayer, molecules like proteins carbs and cholesterol are embedded within and attached on the outside
Function of the cell surface/plasma membrane
Controls the entrance/exit of molecules
Structure of a cell wall (prokaryotes)
Complex, made of tough protein murein
Structure of mesosomes (prokaryotes)
Folds in the cell membrane
Function of mesosomes (prokaryotes)
Large surface area for the attachment of enzymes involved in respiration
Structure of genetic material (prokaryotes)
Single circular loop of DNA
No nuclear membrane
Structure of plasmids (prokaryotes)
Tiny circles of DNA carrying a few genes through cytoplasm
Structure of flagellum (prokaryotes)
Whip like structure
Function of flagellum (prokaryotes)
Allows bacteria to move
Structure of a slime capsule (prokaryotes)
Outside the cell wall
Function of slime capsule (prokaryotes)
A protein stopping cells from drying out
Sticks cells together
Protects cell against the action of a hosts digestive enzymes
What are viruses
Acellular, no cell membrane
Non living, can’t reproduce without a host cell
How do viruses reproduce
In a host cell
Structure of genetic material (virus)
DNA or RNA
Structure of a capsid (virus)
Protein structure
Structure of attachment proteins (viruses)
Allows attachment to a host cell
What are the principals of a light microscope
Focused a beam of light through a convex lens to enlarge image
What are the limitations of a light microscope
Low resolution, lack of focus
Lower magnification, small organelles not visible
Living specimens can be viewed
What are the principals of a transmission electron microscope (TEM)
Thin sample in a vacuum
Beam of electrons passed through
Some are absorbed creating darker spots
Shows internal cell structure
Limitations of of transmission electron microscopes (TEM)
Thin sample is needed
Dead specimen as contained in vacuum
2D image
Black and white image
Principals of a scanning electron microscope (SEM)
Electrons beamed onto a specimen
They scatter depending on contours
Formed 3D image
Limitations of a scanning electron microscope (SEM)
Vacuum so dead specimens only
Black and white image
What’s magnification
How many times larger an image is compared to the object
What’s resolution
The minimum distance between two objects, which still allows them to be distinguished
Equation for magnification
Magnification= size of image/ size of real object
(Size needs to be measure in the same units)
What are artefacts
Something viewed in an experiment but is due to the preparation, eg smudge on a slide
What’s cell fractionation
Cells are broken up to separate the different organelles within
What happens to tissue before fractionation
Cells placed in a solution which is
Cold, reduce enzyme activity which could break down organelles
Isotonic (same water potential), prevent shrinkage or bursting of organelles due to osmosis
Buffered, pH doesn’t fluctuate, could effect enzymes function or structure of organelles
What happens during homogenation
Cells are broken by a blender releasing organelles, large debris is removed through filtration
What’s ultracentrifugation
The homogenate is spun in a centrifuge, initially at a slow speed, heaviest organelles like nuclei are found at the bottom in an sediment, the fluid is removed to be spun again, process repeats
What is the order of organelles according to their densities
Nuclei (heaviest)
Chloroplasts
Mitochondria
Lysosomes
Endoplasmic reticulum
Ribosomes
What are the products of mitosis
Two identical daughter cells, same number of chromosomes as parent cell, except in a rare situation where a mutation occurs, controlled process
What are the products of meiosis
Four daughter cells, cells have half the number of chromosomes of parent cell
What happens in interphase
Cellular activity where DNA is replicated
DNA remains joined at the centromere
What happens during prophase
Chromosomes condense becoming visible
Nucleolus disappears, nuclear envelope breaks down, chromosomes free
Spindle fibres develop from centrioles in animal cells, still develop in plant cells, move to poles of cell
What happens during metaphase
Chromosomes are made up of sister chromatids
Microtubules are attached to centromere causing chromosomes to align across equator
What happens during anaphase
Centromere splits, chromosomes become apart
Sister chromatids move to opposite poles of the cell
Energy is released by mitochondria gathered around spindle fibres
If chemicals which destroy spindle fibres are used, chromosomes remain at equator
What happens during telophase
Chromosomes disappear
Nuclear envelope and nucleolus reforms
Spindle disintegrates
What happens in cytokinesis
Cytoplasm divides
Produces two new cells
What type of cell division occurs in prokaryotic cells
Binary fission
What does binary fission involve
Replication of circular DNA and of plasmids
Division of daughter cells cytoplasm to produce two daughter cells, each have a copy of circular DNA and a number of plasmid copies
How do viruses replicate
Non living, no cell division
Inject nucleic acid, infect host cell, replicates the virus particles
What happens when cell division is uncontrolled
Formation of tumours and cancers
What are cancer treatments focused on
Controlling the rate of cell division
Equation for calculating mitotic index
Mitotic index= number of cells in mitosis/ total number of cells
What’s the difference in structure between the plasma membranes around the cell and membranes surrounding organelles
There is none
Why is the name of the cell surface membrane different to plasma membranes
Cell surface refers to the membrane outside of a cell only
What do phospholipids form in plasma membranes
Phospholipid bilayer
What do the hydrophilic heads in the phospholipid bilayers do
Towards edges of the bilayer, attract water on both sides
What do the hydrophobic tails of the phospholipid bilayers do
Centre of plasma membrane, repel water on both sides
Functions of the phospholipid bilayer
Lipid soluble substances can enter/exit the cell
Prevent water soluble substances entering/exiting cell (maintains water potential)
Membrane is flexible and self sealing
Where are proteins positioned in the plasma membrane
Interspersed
What do proteins on the surface of the bilayer do
Mechanical support to membrane
Act as cell receptors for hormones along with glycolipids
What proteins span the phospholipid bilayer
Protein channels
Carrier proteins
What do protein channels do
Water filled tubes, water soluble ions diffuse across
What do carrier proteins do
Bind to ions or molecules like glucose and amino acids, change their shape to move molecules across membrane
Functions of proteins in plasma membranes
Structural support
Channels to transport water soluble substances across membrane
Carrier proteins allow active transport
Form cell surface receptors to identify cells
Help cells adhere together
Act as receptors for hormones
Where is cholesterol found
Within the phospholipid bilayer
Functions of cholesterol
Add strength to membranes
Reduce lateral movement of molecules, pulls together fatty acids
Membrane less fluid at high temps
Prevent leakage of water and ions , hydrophobic
What’s a glycolipid made of
Carbohydrate covalently bonded to lipid
Carbohydrate portion extends into watery environment outside cell
Functions of glycolipids
Recognition site, extended carb acts as receptor for specific chemicals
Maintain stability of membrane
Helps cells to attach, formation of tissues
What are glycoproteins made of
Carbohydrate chains attached to extrinsic proteins on surface of plasma membrane
Function of glycoproteins
Recognition sites, for hormones and neurotransmitters
Helps cells attach, form tissues
Allows cells to recognise each other eg lymphocytes can recognise an organisms own cells
Why can substances not freely diffuse across the plasma membrane
Not soluble in lipids, can’t pass phospholipid bilayer
Molecules too large to pass through channels
Same charge as protein channels, repelled
Polar molecules have difficulty passing through non polar hydrophobic tails in phospholipid bilayer
Why is the arrangement of molecules in the plasma membrane known as the fluid mosaic model
Fluid, phospholipid molecules move relative to each other, flexible
Mosaic, proteins embedded in phospholipid bilayer are different shapes and sizes
Explain simple diffusion
Passive transport, energy transferred from motion of particles
The net movement of molecules from an area of high concentration to an area of low concentration until evenly distributed
Facilitated diffusion
Allows movement of charged ions and polar molecules through transmembrane channels and transmembrane carriers
Passive process, no external input of ATP, ions move down a conc gradient
Does occur at specific points on plasma membrane where protein channels and carrier proteins are present
How do protein channels work
Water filled hydrophilic channels, allow specific water soluble ions through
Ions bind with protein causing it to change shape allowing ions to pass through to other side
Only open if a specific ion is present
How do carrier proteins work
If molecule is specific to protein present it binds to protein, change of shape, molecule released to inside of membrane
What is osmosis
The movement of water from a high water potential to and area of low water potential through a selectively permeable membrane (plasma membrane)
What’s water potential
Pressure created by water molecules under standard conditions of temp and pressure
What happens to water potential when a solute is added and why
Lowers water potential, more concentrated
Negative value
Explain the process of osmosis
Solute molecules and water molecules move due to their kinetic energy
The selectively permeable membrane only allows water molecules to pass
Water molecules diffuse through the membrane from a high water potential to a low water potential, going down a water potential gradient
When water potential on either side of the membrane is equal, dynamic equilibrium is established, no net movement of water
What’s active transport
The movement of molecules from an area of low concentration to an area of high concentration using ATP and carrier proteins
Why is active transport different from passive transport
ATP is required
Substances go from a low to highs concentration gradient
Carrier protein molecules are involved
Selective process, only specific substances transported
Explain the process of active transport
In plasma membrane carrier proteins bind to a molecule at its receptor site
Inside the cell, ATP binds to protein, hydrolysed into ADP and a phosphate molecule, protein molecule changes shape releasing molecules to other side of membrane
Phosphate molecule is released, protein reverts to original shape
Phosphate molecule recombined with ADP during respiration forming ATP
How does increasing surface area affect the rate of movement across cell membranes
Increases rate
More surface area for the insertion of carrier proteins
What does increasing the number of protein channels and carrier proteins do the rate of movement across cell membranes
Increases rate
Explain cotransport of glucose and sodium ions in the ileum
Sodium ions are actively transported from the epithelial cell into the blood, reduces conc of sodium in epithelial cell
Conc gradient between lumen of ileum and epithelial cell is created, sodium ions move through facilitated diffusion down a conc gradient into the epithelial cell
Sodium ions diffuse through a co transporter protein, so glucose or amino acids also attached, transported to epithelial cell against their conc gradient
Glucose moves down its conc gradient through facilitated diffusion from epithelial cell to blood
What’s co transport
A type of active transport
What allows a cell to be identified
Specific molecules on its surface, includes proteins due to their unique tertiary structure
Protein molecules allow for the identification of what
Pathogens
Cells from other organisms of the same species
Abnormal body cells
Toxins
What’s a non specific defence mechanism
Response is immediate and the same for all pathogens
What are examples of non specific defences
Phagocytosis
Physical barrier eg skin
What’s a specific defence mechanism
Response is slower and specific to each pathogen
Examples of specific defence mechanisms
Cell mediated response, T lymphocytes
Humoral response, B lymphocytes
Why are there lots of different lymphocytes in the body
Different lymphocytes recognise different shapes antigens
What’s an antigen
Proteins located on the surface of cells
Generate immune response by lymphocytes
What’s antigen variability
DNA mutates frequently, shape of antigen can change, previous immunity is no longer effective, memory cells only remembers the shape of old antigen
What happens to lymphocytes that respond to the antigen of self cells
Destroyed before they can mature and differentiate
What is the process of phagocytosis
Pathogens or dead/damaged/abnormal cells release chemicals acting as attractants
Receptors on a phagocytes cell surface membrane allows them to recognise and attach to chemicals on the surface of the pathogen
Pathogen is engulfed forming a vesicle called phagosome
Lysosomes move towards vesicle and fuse
Lysozymes (enzymes in the lysosome) destroy pathogen by hydrolosis
Soluble products are absorbed into the cytoplasm of phagocyte
What’s the cellular response
Response of T-lymphocytes to a foreign antigen on body cells
Is phagocytosis specific or non specific
Non specific
What are T-lymphocytes
Made in bone marrow, nature in thymus gland
Associated with cell mediated immunity, involves body cells
What are B-lymphocytes
Made and matured in bone marrow
Associated with humoral immunity, immunity involving antibodies
What’s the role of antigen presenting cells in cellular response
Phagocytes can distinguish invader cells such as phagocytes which have engulfed and hydrolysed pathogens, body cells invaded by viruses, transplanted cells and cancer cells as they display foreign antigens on their cell surface membrane
Response of T-lymphocytes against infection
Phagocytes engulf pathogen, phagocyte places antigen from pathogen on it’s cell surface membrane
Receptors on a specific helper T cell rapidly divide by mitosis forming clones
These differentiate into memory cells giving rapid response to future infections, stimulate phagocytosis, stimulate B cells to divide into plasma cells and secrete their antibody, activate cytotoxic T cells release protein perforin creating holes allowing substances in and out killing the cell, most effective against viruses
Response of B-lymphocytes to a foreign antigen
B-cells have antibodies on their surface, antigens collide with a complimentary antibody, B-cell take in antigen by endocytosis presenting it on its cell surface
B-cell collides with helper T-cell allowing B-cell to undergo clonal selection
B-cells undergo mitosis, differentiates into plasma cells (makes antibodies) or memory B-cells (divide rapidly to fight reinfection)
Definition of antibody
Proteins with specific binding sites
Describe antibodies structure
Heavy chains- 2 long polypeptide chains
Light chains- 2 short polypeptide chains
Antigen antibody complex- when the antigen bind to the antibody
Variable region- depends on amino acid sequence
Constant region- rest of antibody
How do antibodies lead to destruction of antigens
Agglutination- clump cells together, easy for phagocytes to locate them
Markers- stimulate phagocytes to engulf cells attached to it
How do plasma cells provide a primary immune response
Secrete antibodies, destruction of antigen
How are memory cells a secondary immune response
Rapidly divide producing more plasma/memory cells when encountering a complimentary antigen, long term immunity, increased quantity at a faster rate is secreted
What’s passive immunity
Immunity through antibodies introduced into an individual
No contact with pathogen, immunity is immediate, no memory cells are formed so immunity doesn’t last
Eg antivenom
What is active immunity
Stimulates the bodies antibody production
Contact with pathogen, takes time to develop, long lasting
Natural active immunity, individual infected with pathogen under normal circumstances, antibodies continue to be produced
Artificial active immunity, induces an immune response without having to suffer symptoms of disease eg vaccination
How do vaccines provide protection for individuals
Introduce antigens into the body, stimulates an immune response, memory cells are produced, remain in blood and can divide rapidly if infected in the future
What’s herd immunity
Large proportion of population are vaccinated, difficult for pathogen to spread, unlikely for an at risk individual to come into contact with someone who is infected
What’s the structure of HIV
Lipid envelope with attachment proteins inside
Inside cell is a capsid which includes RNA and enzymes (reverse transcriptase)
How does HIV replicate
HIV enters bloodstream
Protein on HIV binds to CD4 protein found mainly on helper T-cells
The capsid fuses with the cell surface membrane allowing RNA and enzymes from HIV to enter helper T-cell
HIV reverse transcriptase converts RNA to DNA, inserted into helper T-cells DNA
HIV DNA creates mRNA instructing for viral proteins to be made
mRNA exits through nuclear pore, uses helper T-cells protein synthesis mechanisms to make HIV particles
HIV particles break away, it’s cell surface membrane surrounds helper T-cell forming lipid envelope
How does HIV cause symptoms of AIDS
HIV attacks helper T-cells by interfering with its function, without them the immune system can’t stimulate enough B-cells or cytotoxic T-cells, inadequate immune response, a person can be at an increased risk of infection
Why are antibiotics ineffective for viral diseases
Antibiotics prevent bacteria from making cell walls
Viruses rely on host cells to carry out metabolic activity, lack their own metabolic pathways or structures, nothing for antibiotic to disrupt
Viruses have a protein coat not a murein coat so site wont allow antibiotics to work
Viruses embed in a host cells DNA
What’s a monoclonal antibody
A single antibody which has been isolated and cloned
How are monoclonal antibodies target cells by attaching therapeutic drugs to them (direct)
Monoclonal antibodies have specific tertiary structure, they are complimentary to the antigens on a cancer cell for example
Antibodies are given to patient which attach onto receptors on cancer cell
This blocks the chemical signals which stimulate uncontrolled growth
How are monoclonal antibodies target cells by attaching therapeutic drugs to them (indirect)
Radioactive/cytotoxic drugs attached to monoclonal antibody
When the monoclonal antibody binds to the cancer cell it kills it
Ethical issues associated with vaccines
Testing often uses animals
Side effects, benefits should outweigh risk
Everyone needs to be vaccinated for optimal protection, herd immunity
Expense, money could be spent on other research
Trial in a country where disease is common, unknown if successful
Ethical issues witth monoclonal antibodies
Involves mice to produce tumor cells and monoclonal antibodies, induce disease in them, guidelines minimise suffering
Valuable treatment, patients need to be presented with risks and benefits
Testing raises concerns, volunteers need to be aware of risks and the current situation
How do ELISA tests work
Apply a sample to a slide, wash the surface to remove any unattached antigens
Add monoclonal antibodies specific to the antigen, allow them to bind forming antigen antibody complexes, wash to remove any excess antibodies
Add a second antibody (had an enzyme attached to it) which is specific to the first antibody
Add the colourless complimentary substrate to slide, when enzyme acts on substrate a coloured product forms
The intensity of colour depends on the amount of antigen present
