Cell membrane and viruses

Why is the cell membrane is a fluid mosaic model

Fluid= individual phospholipids can move independently

Mosaic= embedded with proteins and many molecules

Draw cell surface membrane

Intrinsic proteins

Act as transport IN and OUT of the cell e.g.

Channel proteins and carrier proteins

They act as receptors to identify cells and allow them to attach to each other

Extrinsic proteins

Mostly found on the outside of phospholipid bilayer e.g. glycoproteins

These allow cells to communicate with other cells and to be recognised by the immune system and to act as receptors for hormones to enable cells to attach to each other to form tissues

Glycolipids

Made of carbohydrate covalent bonded to a lipid.

The carbohydrate section extends into the tissue fluid and acts as a receptors for chemicals, recognition sites, maintains the stability of the membrane and can attach to other cells forming tissues

Aquaporin

Instrinsic protein which allows the transport of water in and out the cell by osmosis

Cholesterol

Maintains integrity of the phospholipid bilayer

Reduces lateral movement of molecules in cell membrane and makes membrane less fluid and more rigid at warm temperatures.

Prevents the leakage of water and dissolved ions from the cell

Why do phospholipids form a bilayer

Fatty acid tails are hydrophobic and non polar so orientate themselves as far away from polar environment of tissue fluid and cytoplasm. Phosphate heads are polar so interact with polar environment of tissue fluid and cytoplasm

Why do phospholipids form a bilayer but not triglycerides

Trilglyerciees are entirely hydrophobic / non polar

What are all the 5 structures of a virus

1. RNA strand

2. Capsid

3. Lipid envelope

4. Attachment protein

5. Reverse transcriptase

Function of RNA strand

Template for DNA formation

Function of the capsid

Protects the RNA

Function of the lipid envelope

Fuses with host cell membrane

Function of attachment protein

Identify host cell so enables virus to attach to the host cell

Function of reverse transcriptase

Makes DNA from RNA template

Viral replication

1. Attachment proteins attach to receptors on host cell

2. Viruses inject (DNA/ RNA) nucleic acid into host cell

3. Host cell replicates viral nucleic acid (DNA/ RNA)

4. Host cell produces viral protein/capsid/ enzymes

5. Viruses are assembled and released from the cell

What does HIV and AIDs stand for

HIV = human immunodeficiency virus

AIDs = acquired immune deficiency syndrome

What is HIV host cell

T helper cell

Labelled diagram of HIV

Process of HIV replication

1. Attachment proteins of HIV bind to a protein receptor on a helper T cell surface membrane

2. Lipid envelope and protein capsid fuses with the cell surface membrane.

3. This enables RNA and enzymes of HIV to enter T helper cell

4. The HIV reverse transcriptase concerts the viruses RNA into DNA

5. The HIV DNA is moved into the helper T cells nucleus and is inserted into the cells DNA

6. HIV DNA in nucleus is transcribed into mRNA ( contains instructions for making new viral proteins and RNA go into a new HIV)

7. The mRNA passes out the nucleus through a nuclear pore and uses the cells ribosomes to be translated into HIV proteins

8. New HIV viruses are assembled into new viruses and released from the t helper cell

How is HIV transmitted and what are the symptoms of HIV

• Transmitted by bodily fluids like semen, blood and vaginal secretions through unprotected sex and direct blood to blood contact

• Symptoms are flu like but virus can remain dormant in DNA for years so can go undetected

When does a person have aids

• when the immune system deteriorates and fails so critically low number of T helper cells

• Less then 200 cells/mm3

• Individuals become more susceptible to infection which leads to death

How to diagnose HiV

Blood sample then elisa test to detect HIV antibodies

How to diagnose aids

Blood sample taken then number of T helper cells is counted and have aids when count below 200cells/mm3

How does HIV/ AIDs impact the immune system

• HIV host cell are T helper cell and replication of HIV virus kills the T helper cell

• Reduction in number of T helper cells means it cannot release cytokines and cannot activate B plasma cells

• Therefore cannot make antibodies

• T killer cells cannot kill cells infected with pathogens

AIDs and secondary infections

AIDs weakens the immune system so sufferers can develop secondary diseases due to opportunistic infections and the opportunistic infections kill individual

Why can we use antibiotics to treat bacterial infections

Antibiotics inhibit enzymes that make murein in the cell wall so bacteria cannot make cell wall or cell wall is weakened so more water can enter by osmosis causing the cell to burst killing bacteria

Why are antibiotics Ineffective against viral disease

• Virus has a capsid not a murein cell wall so no sites where antibiotics work

• virus is inside host cell so antibiotics cannot reach them

• No metabolism so cannot disrupt metabolic mechanisms

Give the three structural features found in all virus

RNA

Capsid

Attatchment protein

Explain why viruses are described as acellular and non living

• Acellular as no cell surface membrane and not made up of cells

• Non living as have no metabolism/metabolic reactions so cannot independently respire