ALL of Cells 3.2 Aqa

Describe the structure of the nucleus

Nuclear membrane- that is a double membrane

Nuclear pores

Nucleoplasm -jelly like

Chromosomes- associated with histones

Nucleolus - smaller sphere inside, site of rRNA production and ribosomes.

Describe the function of the Nucleus

Site of DNA replication and transcription

Making mRNA

Contains the genetic code for each cell.

Describe the structure of the Endoplasmic reticulum (both smooth and rough)

Both have folded membranes called cisternae

Rough has membrane bound ribosomes on the cisternae

What is the function of RER?

Protein synthesis

What is the function of SER?

Synthesis and storage of lipids and carbohydrates

Describe the structure of the Golgi Apparatus

Folded membranes called cisternae

Secretory vesicles that are pinched off from the cisternae

What are the many functions of the Golgi Apparatus?

Add carbohydrates to a proteins to form a glycoproteins

Produce secretory enzymes

Secrete carbohydrates

Transport, modify and store lipids

Form lysosomes

Create vesicles which transport productsM where the vesicles fuse with the cell membrane and the products are released outside.

Describe the structure of lysosomes

Sacks of lysozymes, digestive and hydrolytic enzymes

What is the function of lysosomes?

Digest worn out organelles so the materials are reused.

Exocytosis-destroy outside material

Autolysis- destroy dead cells

Fuse-with a phagosome to form a phagolysosome And

Hydrolyse pathogens

Describe the structure of the mitochondria

Double membrane

Inner membrane has a large surface area and called CRISTAE (do not confuse with cisternae)

Matrix - fluid in the inner membrane

Have their own Circular DNA

Have their own 70s ribosomes

What is the function of the mitochondria

Site of aerobic respiration

Site of ATP production

Has their own mitochondrial DNA to code for enzymes needed in respiration

Describe the structure of the ribosome

Made up of 2 sub units Of protein and rRNA

What is the function of the ribosome?

Protein synthesis

What are the two types of ribosomes in eukaryotic cells and where do you find them?

80s- large ribosomes- found in eukaryotic cells

70s- small ribosomes- found in prokaryotic cells, mitochondria and chloroplasts

Describe the structure of the vacuole

Fluid filled and surrounded by single membrane called the tonoplast

What is the function of the Vacuole?

Provide the plant cell turgidity, which provides support

Temporarily store sugars and amino acids

Contain pigments which colour petals, which attract pollinators

Describe the structure of a chloroplast

Surrounded by a double membrane

thylakoids-fluid filled sacs, contain photosynthetic pigments which stack up to form granum

Grana- Granum (plural)

Lamella/Lamellae (plural)- membrane channels that connect the grana

Fluid filled stroma - contains enzymes, sugars, 70s ribosomes and its own chloroplast DNA

Starch grains - glucose store

What is the function of chloroplasts? (2 marks)

The site of photosynthesis

Light dependant reaction in the thylakoid membrane

Light independent reaction in the stroma

What is the structure of the cell wall in plants and fungi?

Plants- cellulose

Fungi-chitin

What is the function of the cell wall?

Provide structural strength to the cell

What is the structure of the cell membrane?

Phospholipid bilayer that’s embedded with proteins, cholesterol, carbohydrates

What is the function of the cell membrane?

Controls what enters and exits the cell

Describe the structure of prokaryotic cells

Plasma membrane,

cell wall of murein,

slime capsule,

flagellum/flagella (plural)- for movement

Plasmids- carry extra genes for survival

Circular DNA

70s ribosomes

Cytoplasm

Much smaller

What are the differences between prokaryotic cells and eukaryotic cells?

Prokaryotic cells are…

Much smaller

Have no membrane bound organelle

Smaller 70s ribosomes

Circular DNA that is not associated with histones, no nucleus

Cell wall is made of murein

They also contain plasmids, a slime capsule and one or more flagella

What are viruses described as?

Non-living- no metabolic reactions or movement

Acellular- not made of cells and no cell membrane

Describe the structure of viruses

RNA or DNA

Capsid- contains the genetic material and any enzymes

Attachment proteins- to attach to the cell receptors on a host cell

May have a lipid envelope- which they take from the host cell

Smaller than bacteria

What are the the three types of microscopes?

Optical

Scanning electron

Transmission electron

Define magnification

How many times larger the image is compared to the object

Define resolution

The minimum distance between two objects, which can still be viewed as separate. And is determined by the wavelength

• What are the differences between the Optical microscope and Electron microscopes?

1. Light- A beam of light is condensed to crate an image

   Electron- a beam of electron is condensed to create an image. Electromagnets are used to condense the beam

2. Light- poor resolution

   Electron- high resolution, because electrons have a shorter wavelength

3. Light- low magnification

   Electron-high magnification

4. Light- Coloured images

   Electron- black and white images

5. Light- Can view living samples

   Electron- Samples must be dead

6. Light- Easy to use

   Electron-need to be used in a vacuum and very expensive

describe the TEM (Transmission Electron Microscopes)

Need very thin specimens

2D image

An electron gun produces a beam of electrons that pass through the specimen

Denser parts absorb more electrons and appear darker

Describe the SEM (Scanning Electron Microscope)

Thick specimens can be used

Electrons are beamed on the surface and reflected

3D image

What is the formula for magnification?

Magnification= Image size/Actual size

How do you calibrate an Eye piece graticule?

Use a stage micrometer

1. Line up the stage micrometer and eye piece graticule when looking down the lens

2. Count how many divisions on the eyepiece graticule fit ONE division of the micrometer

3. Each division on the micrometer is 10 micrometers, calculate what One division is on the eye piece graticule at the current magnification.

A student used an eyepiece graticule, and observed that 20 micrometers measure 2.35 divisions on the graticule

Calculate the diameter of the nucleus if the nucleus measures 1.4 graticule divisions (2 marks)

(20/2.35)x 1.4= 11.91 micrometers

What solution do cells need to be out in before cell fractionation? And explain why (2 marks)

Cold- reduce enzyme activity

Isotonic- to maintain the water potential of the cells, so cells do not shrivel or burst

Buffered- maintain pH levels, otherwise the organelles can be damaged

Describe the process of cell fractionation

Homogenisation

1. Organelles are released as the Cells are broken open by a homogeniser

2. Creating a homogenate

Filtration

1. Remove debris

Ultra centrifugation

1. The filtrate is spun in a centrifuge causing the heaviest organelles to form a pellet at the bottom

2. Which can be removed

3. This is repeated at increasingly higher speeds until the desired organelles form a pellet

What is the order of organelles from heaviest to lightest?

1. Nuclei

2. Chloroplasts

3. Mitochondria

4. Lysosomes

5. Endoplasmic reticulum

6. Ribosomes

How many times do you need to centrifuge to isolate the mitochondria?

The third spin

How do Eukaryotic, Prokaryotic and Viruses replicate?

Eukaryotic- mitosis and meiosis

Prokaryotic- binary fission

Viruses- replicate in host cells and using the cell’s machinery

Describe the process of Binary fission (3 marks)

The circular DNA and plasmids are replicated

The cytoplasm splits to creat 2 daughter cells

Each daughter cell has one copy of the circular DNA but a varying number plasmids

What are the 4 stages in the cell cycle?

G1- Interphase- growth

S-phase - Interphase- DNA replication, Organelles double and cell grows bigger

G2- Interphase-preparation for mitosis

M-phase- mitosis and cytokinesis

Which is the longest stage in the cell cycle?

Interphase- when the organelles double, DNA replicates and the cell grows bigger

Explain what happens in Prophase

The chromosome condense, becoming visible when stained

Centrioles move to opposite poles

What happens in Metaphase

Chromosomes line up along the equator,

Spindle fibres attach to the centromeres of the chromosomes

What happens in Anaphase?

Spindle fibres retract and the Centromere splits

pulling the chromatids to opposite poles

What happens in Telophase and Cytokinesis?

Spindle fibres disintegrate and the chromosomes start to condense again

Nucleus starts to reform, cytoplasm splits forming 2 identical daughter cells

What is the formula for the mitosis index?

Mitosis index= number of cells IN mitosis/total number of cells IN view

How does disruption in mitosis cause cancer?

Disruption in the control of mitosis can result in uncontrolled cell division

Which can result in tumour cells (malignant or benign)

Why is the cell meme range described as the fluid mosaic model?

Due to the unsaturated fatty acid chains in the phospholipids allowing the phospholipid bilayer being able to move

And the arrangement of proteins, carbohydrates, glycoproteins and glycolipids that are embedded in it.

Why is the cell membrane described as partially permeable?

Small lipid soluble non-polar substances can pass through the phospholipid bilayer through simple diffusion

Large, water soluble, polar molecules cannot

What is the role of cholesterol in the cell membrane?

Restricts the lateral movement of phospholipids, making it less fluid at high temperature

This it’s important as it stop substance from leaking out.

Describe Simple diffusion

The movement of molecules from an area of high concentration to an area of low concentration

Until equilibrium is reaches

No ATP

Must be small, lipid soluble and non-polar molecules

Describe facilitated diffusion

Passive process

Large, water soluble, polar molecules

Channel proteins and Carrier proteins

What are channel proteins

Tubes that are filled with water allowing water soluble ions to pass through

What are carrier proteins?

Can change its shape and its affinity to bind to a molecule

What is Osmosis?

• The net movement of water molecules from an area of high water potential to an area of low water potential

• across a partially permeable membrane

What is water potential?

It is the pressure created by water molecules and is measured in kPa

What value of water potential does pure water have?

0 kPa

What does isotonic solution mean?

The water potential of the solution is the same as the water potential of the cell

Animal cells are normal

Plant cells are flaccid

What does a hypotonic solution mean?

The water potential is higher in the solution than the water potential in the cell

Therefore can cause the animal cells to burst (cytolysis)

Plant cells to become turgid

What does a hypertonic solution mean?

The water potential of the solution is lower than the water potential in the cell

Animal cells become shrivelled

Plant cells become Plasmolysed

What is active transport?

• The movement of substances from low to high concentrations

• Requires ATP and carrier proteins

Describe the process of active transport by the sodium potassium pump (6 marks)

3 Na+ ions bind the the carrier proteins binding site. ATP attaches to the carrier protein

As ATP is hydrolysed it release energy

Causing the carrier protein to invert and lower its affinity for sodium

So the Sodium ions to be released on the other side

2 K+ ions bind to the carrier protein

Causing the carrier protein to revert back and increase its affinity for sodium

Releasing the potassium ions and the inorganic phosphate

Describe the process of co-transport of sodium ions and glucose in the ileum

1. Sodium ions Na+ are actively transported out of the epithelial cell into the blood by the sodium potassium pump.

2. The movement of Na+ provides energy for glucose to move against its conc. gradient

3. Reducing the conc. of Na+ in the epithelial cell and establishing a conc. gradient.

4. So Sodium and glucose bind to the co-transporter

5. The binding of both and the energy from the diffusion causes the co-transporter to invert which moves both of them across the cell membrane

6. Releasing both Sodium and glucose in the cell.

How do lymphocytes identify pathogens and self-cells?

Cells have proteins on the cell membrane which are complementary to the cell receptors on the lymphocyte.

What are the three cells which can trigger an immune response?

Pathogens-(bacteria, viruses and fungi)

Foreign cells

Cancer cells

Toxins

Definition of an Antigen (2 marks)

Antigens are foreign proteins that trigger an immune response by the lymphocytes

They are located on the surface of cells

What is Antigen variability?

When the pathogen’s DNA mutates frequently, and the gene which codes for the antigen mutates.

Causing the shape of the antigen to change

This causes any previous immunity to no longer be effective as the memory cells have the memory of the OLD antigen shape

What are the 2 types of macrophages?

Phagocytes- non-specific

Lymphocytes- specific

Describe the process of phagocytosis and what kind of response is it?

Non-specific

Any foreign cell will trigger phagocytosis

Receptors attach to the chemicals or antigens on the pathogen

The phagocyte changes shape and moves around and engulfs the pathogen

Once engulfed the pathogen is contained in a phagosome vesicles

The Phagosome fuses with a lysosome forming a phagolysosome. Releasing the lysozymes which hydrolyse and breakdown the pathogen. And any useful substances are re used by the phagocyte

How can a phagocyte become a Antigen presenting cell after phagocytosis?

The antigens from the hydrolysed pathogen are the presented on the cell surface to signal the presence of the pathogen to the lymphocytes

What are T lymphocytes?

T Lymphocytes which are white blood cells

Involved in the specific immune response and the cell mediated response

Where are lymphocyte made in? What about T cells?

All lymphocytes are made in the bone marrow

But T lymphocytes mature in the thymus

Describe the cell mediated response

1. Helper T cells have receptors on their cell surface which attach to the antigens on an APC

2. Once attached it activates the helper T cells to divide by mitosis

3. To replicate and make a large number of T helper cell clones

4. Which can differentiate into T helper cells (ones that activate B lymphocytes and ones that stimulate macrophages to perform phagocytosis)

5. cytotoxic T cells

How do cytotoxic T cells destroy abnormal or infected cells?

They release a protein called perforin

Which embeds in the cell surface membrane which makes a hole

So that any substances can enter and leave the cell

Causing cell death

What type of infection is cell death the most common immune response?

Viral infections, because viruses infect body cells

What are B Lymphocytes? And how are they activated?

B cells are white blood cells involved in the specific immune response.

Antigens in the blood collide with the complimentary antibody on a B cell, the B cell takes an antigen by endocytosis, and the presents it on a cell surface membrane.

A t helper cell will cause the B-cell to mature and differentiate into plasma cells and memory B cells

What do plasma cells do?

Secrete antibodies

What can B memory cells do? And how do they provide active immunity?

They can quickly divide by mitosis and differentiate into lots of plasma cells

This results in a large number of antibodies being produced rapidly, destroying the pathogen before symptoms can occur.

Explain the curves in the graph

1. The first exposure to the pathogen

Takes a longer period of time for the b cells to collide with the antigen, clonal expansion and differentiation.Takes longer to make antibodies, lower rate of antibody production

2. The second exposure

   Memory b cells can divide rapidly and differentiate into plasma cells. Large quantity of antibodies and high rate of antibody production.

Draw and describe the structure of an antibody

Explain how the structure of an antibody relates to its function (2 marks)

Antibodies have strong disulphide bridges and hinge regions which give it flexibility.

Allowing the binding sites to bind to multiple antigens and agglutinate.

Describe differences and similarities of passive immunity and active immunity

1. Passive immunity

• Where someone receives antibodies

• Short term immunity

  2. Active immunity

• antibodies are created by your immune system due to exposure to a pathogen or antigen.

• Long term immunity

Give an example of passive and active immunity

Passive- antibodies in the mothers breast milk being past down to the baby

Active- vaccines provide artificial active immunity, where a small amount of dead or inert version of the pathogen is given. The antigens activate the B cells to undergo clonal expansion and differentiation.

So when there is an exposure to the real pathogen the memory b cells can rapidly divide and differentiate into plasma cells and make large quantities of antibodies

Describe herd immunity and which people are vulnerable?

When a large numbers of the population are vaccinated, and the pathogen cannot spread among the population

protecting those who are vulnerable.

Such as elderly people, people with immunodeficiencies, cancer patients, immunocomprimised patients,

What type of virus is HIV and describe its structure

It’s a retrovirus

Lipid envelope- taken from host cell

Capsid- which contains reverse transcriptase enzymes and RNA for viral replication

Attachment proteins- to enable the virus to attach to the helper T cells

Describe the process in which HIV replicates in helper T cells (6 marks)

1. HIV is transported in the blood until it attaches to a CD4 protein on a T helper cell

2. HIV fuses with the membrane releasing the capsid inside which releases the RNA and reverse transcriptase

3. Reverse transciptase copies the RNA into a DNA copy

4. Which combines with the host DNA in the nucleus

5. Here mRNA is transcribed by ribosomes and undergoes protein synthesis using th whist cells machinery ti the create new viral proteins

6. Which are assembled to form new viral particles

7. Which then bud off from the cell membrane or are released when the cell bursts

State 3 symptoms of AIDS

Weight loss

Fever

chronic infections

How does AIDS occur?

When HIV has destroyed many T helper cells and the immune system is weaker, making the body more susceptible to infection and disease.

How does HIV viruses weaken the immune system?

They decrease the number of T-helper cells

Therefore less b cells are stimulated to differentiate into plasma cells to produce antibodies against infections

Increased chance of infections

Less cytotoxic t cells are stimulated to kill and destroy infected cells, cancer cells or foreign cells through apoptosis, increased risk of cancer.

How do monoclonal antibodies differ from regularly antibodies?

They are single type of antibody that has been isolated and cloned.

Describe the process of direct monoclonal antibody therapy in cancer treatments

Where the monoclonal antibodies binding site is complementary to the antigens on cancer cells and not normal cells

This prevents chemicals from binding to cancer cells which enable uncontrolled cell division

Therefore preventing the cancer cells from growing

Describe Indirect monoclonal antibody therapy in targeted cancer medication

When a cancer drug is attached to the monoclonal antibodies, and the drugs are delivered directly to cancer cells and kill them.

Less harmful side effects

Give 4 examples that monoclonal antibodies can be used in

Direct monoclonal antibody therapy

Indirect monoclonal antibody therapy

Testing for pregnancy

Testing for Covid 19

What does ELISA stand for?

Enzyme linked immunosorbent assay

What does the indirect and direct ELISA test detect for?

Indirect- detects for antibodies

Direct- detects for antigens

Describe the process of the indirect ELISA (used to measure antibodies)

Add the patients sample in to an antigen coated well

Then Wash it to remove any unbound antibodies

Then add a secondary antibody which has enzymes attached to it

Then wash to remove any unbound antibodies

Add the complementary substrate, which will form an enzyme substrate complex and cause a colour change

measure the colour

Describe the process of a direct ELISA test (used to measure antigens)

Add the patients sample in to an antibody coated well

Then Wash it to remove any unbound antigens

Then add a secondary antibody which has enzymes attached to it

Then wash to remove any unbound antibodies

Add the complementary substrate, which will form an enzyme substrate complex and cause a colour change

measure the colour

What is another name of a direct ELISA test.

Sandwhich ELISA