cell structure topic 2 Flashcards
describe the structure of nucleus
- Nucleus is a double membrane called the envelope containing ~3000 nuclear pores
that enables molecules to enter and leave. It also contains chromatin and a nucleolus
which is the site of ribosome production.
A granular jelly like material called
nucleoplasm makes up the bulk of the nucleus.
function of nucleus
-site of Mrna transcription
-semi conservative replication
-mitosis
-gene expression
describe the function of mitochondria
site of aerobic respiration which produces ATP
describe the structure of mitochondria
Mitochondria are oval shaped, bound by a double membrane called the envelope.
The inner membrane is folded to form projections called cristae with a matrix on the inside
containing all the enzymes needed for respiration.
describe the structure of chloroplast
surrounded by a double membrane
-had thylakoids ,folded membranes containing pigment)
-fluid filled stroma containing enzymes for photosynthesis
describe the structure of lysomes
-bags of digestive enzymes
describe the function of lysosome
hydrolyse phagocytic cells
break down dead cells (autolysis)
-exocytosis -release enzymes to outside the cell to defeat the material
-
describe the structure of ribosomes
made up of two sub units -protein and Rna
80S - found in eukaryotic cells (larger ribosomes )
70S found in prokaryotes
site of protein synthesis
describe the structure of endoplasmic reticulum
has folded membranes called cisternae
rough ER has ribosomes on the cisternae
describe the structure of the Golgi apparatus
folded membranes making cisternae
Golgi vesicles pinch of cisternae
describe the function of the golgi appararus
synthesises for glycoproteins
modifies proteins
produces lysosomes
describe the function of the rough and soft endoplasmic reticulum
SER- stores lipids and carbohydrates
RER- synthesis of proteins
describe the function of soft endoplasmic reticulum
SER- stores lipids and carbohydrates
describe the cell surface membrane
begins with a phospholipid bi layer which forms due to the hydrophillic and hydrophobic interactions
hydrophobic inwards
hydrophilic outwards
What is the function of the phospholipid bilayer
allow lipid-soluble substances to enter and leave the cell
• prevent water-soluble substances entering and leaving the cell
• make the membrane flexible and self-sealing
what is found in the bilayer
intrinsic and extrinsic protein
glycoproteins
cholesterol
glycolipids
what are intrinsic proteins
they bind to ions like glucose or amino acids ,change shape ,in order to move across membrane
what is co-transport
occurs when two substances are simultaneously transported across a membrane
This occurs particularly in epithelial cells of the ileum.
Describe cell specialisation
In multicellular organisms, cells become specialised to carry out specific functions
What are the features of prokaryotic cell
Cell wall:
Capsule:
Cell-surface
Circular DNA:
Plasmids:
Flagellum
What is a capsule
some bacteria have a capsule made of slime
Helps protect bacteria from attack and allows groups of bacteria to stick together
What is plasmid
small extra loops of DNA that carry genes that can help with survival eg antibiotic resistance
What is flagellum
a long hair-like structure found in some species (some prokaryotes can have more than one)
used to make the cell move
Describe the virus and its structure
Viruses are non-living and acellular (not cells)
Made up of nucleic acids (DNA or RNA) surrounded by a protein coat called a capsid
Attachment proteins are found on the surface of the virus to allow it to attach to and enter a host cell
What are the two types of cell division in eukaryotes
There are two types of cell division in eukaryotes: mitosis and meiosis
What is the main difference between mitosis and meiosis
Mitosis produces two identical ‘daughter’ cells for growth or repair of tissue
Meiosis produces four genetically different daughter cells for reproduction
What does the cell cycle consist of
The cell cycle consists of interphase and mitosis
What are the four stages of mitosis
Prophase
Metaphase
Anaphase
Telophase
Describe what happens during prophase
chromosomes condense and become visible
centrioles move to opposite ends of cell and start forming a network of fibres called the spindle
nuclear envelope breaks down and chromosomes are free in the cytoplasm
What happens during metaphase
The chromosomes line up along the equator (middle) of the cell and attach themselves to the spindle via their centromere
What happens during anaphase
The centromeres divide and the sister chromatids separate
Each sister chromatid is pulled to the opposite end of the cell
What happens during telophase
The chromosomes reach their respective poles and become longer and thinner
The nuclear envelope reforms
The cell become longer and thinner in the middle and eventually splits into two
How can cancer treatments become unaffective
however this also targets normal body cells that are rapidly dividing
Describe the process of binary fission
1.The circular DNA replicates once and plasmids replicate multiple times
2.The cell gets bigger and the loops of DNA move to opposite poles of the cells
3.The cytoplasm divides and a new cell membrane and cell wall begins to form
4.Two ‘daughter’ cells are formed, each with one loop of circular DNA and a variable number of plasmids
Describe how viruses replicate
Viruses are non-living so they cannot replicate by themselves
They use a host cell to replicate
1.The attachment proteins bind to complementary receptors on the cell-surface membrane of the host cell
2.They then inject their DNA or RNA into the host cell and it
3.reverse transcriptase converts RNA into DNA
4. begins producing new viral components which are assembled into new viruses
What is resolution
Resolution: a measure of how detailed the image is
Describe magnification
Difference in size between the image and the real object
What are two main types of microscopes
Light and electron
What is the difference between electron microscope and light microscope
Light microscopes
- uses light to form an image
-lower magnification (x1500)
-lower resolution (x 0.2)
Electron microscope
-uses electrons to form an image
-higher magnification (x1,500,000)
-higher resolution (x0.0002)
What are two types of electron microscopes
TEM and SEM
How does Transmission electron microscope work
Uses electromagnets to focus electrons into a beam
that passes through a thin section of the specimen and onto a screen behind
to form a photomicrograph
How is an image formed using TEM
Denser areas of the specimen absorb more electrons and so appear darker
What are the pros and cons of transmission electron microscopes
Pros: Extremely high-resolution images
Cons: Can’t use living specimens, specimen must be extremely thin, high-energy electron beam could damage specimen, image is not in colour, image is 2D, artefacts can form on image
How do scanning electron microscopes work
Uses electromagnets to scan the beam of electrons over the surface of the specimen
Electrons are scattered and with computer analysis, a 3D image can be produced that show the surface of the specimen
What are the pros and cons of scanning electron microscopes
Pros: Can use thicker specimens than TEM, resulting image is 3D
Cons: Can’t use living specimens, specimen must be extremely thin, a, high-energy electron beam could damage specimen, image is not in colour, lower resolution than TEM
What is cell fractionation
Cell fractionation is a method of breaking cells up and separating the components
What are the three steps of cell fractionation
1.Homogenisation
2.Filtration
3.ultracentrifugation
Describe the process of homogenisation
1.can be done by grinding the cells in a blender or vibrating them
2.The solution should be ice-cold
and isotonic (same pH as cell - use a buffer)
In the homogenisation process ,why must the solution be ice cold
(to reduce activity of enzymes that may break down organelles)
Describe why filtration takes place
To removing complete cells and debris)
Why does ultracentrifugation occur
To separate the organelles
Describe the process of ultracentrifugation
1.Pour cell fragments into a test tube and put the test tube into a centrifuge
2.Spin the centrifuge at low speed
- The heaviest organelles (nuclei) are forced to the bottom to form a thick sediment called the pellet
4.The liquid above is called the supernatant and is transferred to another test tube to be spun again
5.Spin the centrifuge faster to isolate the the mitochondria in the pellet then drain the
supernatant to spin again
6.Continue the process to isolate the next heaviest
What is the order organelles are separated
1nuclei,
2mitochondria,
3lysosomes,
4endoplasmic reticulum, and
5 then ribosomes
What is the cell surface membrane made up of
Cell surface membranes are made up of a phospholipid bilayer with other molecules embedded in it such as
proteins, glycolipids, glycoproteins, and cholesterol
What are the two functions of a protein in a phospholipid bilayer
1.for mechanical support or act as receptors for eg hormones
- can be channel or carrier proteins to transport substances in and out of cells
What are the 2 roles of glycolipids
They act as cell-surface receptors and also help to maintain the stability of the membrane
They can also allow cells to bind together to form tissues
What are the two roles of glycoproteins
They act as receptors/recognition sites and help cells bind together to form tissues
They also allow immune cells to recognise self cells so they don’t get attacked
What are the two roles of cholesterol in bilayer
they increase the strength of cell surface membrane by:
They pull the hydrophobic tails of the phospholipids together which limits their movement,
which makes the membrane more rigid especially at high temperatures
This helps to maintain the shape of animal cells
Describe simple diffusion
It is a passive process (does not require energy from ATP)
occurs when the molecule can move freely through the cell-surface membrane
This occurs for small, non-polar molecules such as oxygen and carbon dioxide
Describe facilitated diffusion
Facilitated diffusion involves the use of channel and carrier proteins
Large molecules and charged ions aren’t able to move via simple diffusion as they can’t pass through the lipid membrane
Instead, they move through channel or carrier proteins down a concentration gradient
How do Chanel proteins and protein carriers work
Channel proteins form pores that allow a specific molecule to pass throug
Carrier proteins change shape when a specific molecule binds to them and
Describe osmosis
It is the movement of water from an area of high water potential to an area of low water potential
It is a passive process (doesn’t require energy from ATP
How can you increases the rate of osmosis
To increase the rate of osmosis, increase the water potential gradient,
make the exchange surface thinner,
and increase the surface area of exchange surface
Is active transport an active process or passive
It is an active process (requires energy from ATP)
Describe how carrier proteins are used in active transport
1.The molecule or ion binds to a specific carrier protein
2.ATP breaks down into ADP and a Pi group which releases energy to change the shape of the carrier protein
3.The molecule/ion is deposited in the cell and the carrier protein reverts to its original shap
What is co transport
One of the molecules moves down its concentration gradient and this moves the other against its concentration gradient
What is an example of co transport
Sodium moves into the cells down its concentration gradient and this moves glucose in as well, against its concentration gradient.
Describe antigens and the two types of antigens
All cells have antigens on their surfaces that allows them to be recognised by other cell
The immune system can distinguish antigens on body cells (self) and antigens on foreign objects (non-self)
What are two types of abnormal cell
Cancerous
Infected cell
Describe phagocytosis
1.The phagocyte attaches to the receptors on the surface of the pathogen and recognises the foreign antigens
2.The cytoplasm of the pathogen engulfs the pathogen inside a membrane called a phagosome
3. Lysosomes fuse with the phagosome and break down the pathogen
4.The phagocyte displays the pathogen’s antigens on its cell-surface membrane and is referred to as an APC
What are the three main stages of immune response
phagocytosis,
cell-mediated response, and
humoral response
Describe T cells
T cells are a type of immune cell
There are two types of T cells: helper T cells and cytotoxic T cells
outline the process for cell mediated response
- complementary helper T cells bind to antigen on antigen presenting cell
2.release cytokines that stimulate clonal expansion of complementary helper t cells and become memory cells or trigger humoral response - clonal expansion of cytotoxic T cells : secrete enzyme perforin to destroy infected cells
what does cyto toxic cells do
When they find an infected cell, they inject it with perforin
which causes the cell membrane to disintegrate and the cell to die
outline the humoral response
1.Complementary helper t cell binds to foreign antigen on antigen presenting cell
2.Release cytokines that stimulate clonal expansion of complementary B cells
3.B cells differentiate into plasma cells
4. Plasma cells secrete antibodies with complementary variable region to antigen
Describe what an antibody is
Antibodies are proteins made by B-cells that have a binding site complementary to antigens on a specific pathogen
Describe the structure of an antibody
Antibodies are made of four polypeptide chains,
two called heavy chains and
two called light chains.
They each have two binding sites
What are the three roles of an antibody
cause agglutination (pathogens stick together so they can be engulfed easier)
act as markers to stimulate the phagocytes to engulf the pathogen
neutralise the pathogen so it can’t enter any body cells
What is the role of memory B cells
Memory B-cells activate the secondary immune response in case the pathogen attacks again
If it encounters the pathogen again, it will:
undergo clonal expansion,
differentiate into plasma cells
and release antibodies
How does antigenic variation prevent secondary response
The changing of their surface antigens this means that the secondary immune response won’t be triggered
What is active immunity
Active immunity is when the immune system produces its own antibodies and memory cells
Describe the difference between artificial active immunity and natural active immunity
Natural active immunity: after you catch a disease, you become immune
Artificial active immunity: after you get a vaccine containing dead or weakened pathogens
What is passive immunity
Passive immunity is when the body receives antibodies from a different organism
Describe artificial passive immunity and natural passive immunity
Artificial passive immunity: after you get a vaccine containing antibodies against a pathogen
Natural passive immunity: after a baby receives antibodies from its mother in breast milk or through the placenta
Outline the difference between passive immunity and active immunity
Active
-Involves exposure to the pathogen’s antigens
-Memory cells are produced
-Protection is not immediate
-Immunity is long term as memory cells are formed
Passive
-Does not involve exposure to antigens
-No memory cells are produced
-Protection is immediate
-Immunity is short term as after a while, the antibodies are broken down
Describe the structure of HIV
HIV (Human Immunodeficiency Virus) is made up of two single strands of RNA
enclosed in a capsid
surrounded by a lipid envelope
in which are embedded attachment proteins
How do aids develop in people with HIV
HIV infects and kills helper T cells and
eventually this leads to weakened immunity which is AIDS (Acquired Immune Deficiency Syndrome )
Why do individuals with HIV more susceptible to other secondary diseases
HIV kills helper T cells
Which are needed for the formation of B cells
So less B cells are made and
less antibodies made
explain the principle of vaccination
1.vaccine contains dead form of pathogen
2.triggers primary immune response
3.memory cells are produced and remain in the blood stream ,so secondary response is rapid and produces higher concentration of antibodies
4. pathogen is destroyed before it causes symptoms
contrast primary immune response and secondary immune response
- faster rate of antibody production
- shorter time lag between exposure and antibody production
- higher concentrations of antibody
- antibody level remains high after the secondary response
