pathogens and viruses

Question 1

what are pathogens

Answer 1

disease causing microorganisms , including bacteria virus , fungi

Question 2

describe a virus

Answer 2

• non living
  -accelular
  -no nucleus , no surface membrane , no cytoplsm
  -always contains dna or ran
  -always contain a capsid
  -attatment proteins

Question 3

describe the replication of virus

Answer 3

-1) virus attach to SPECIFIC host cells using attachment proteins which are comp to receptors

2) virus injects nucleic acid into host cells

3)the genetic material codes for more virus particles which are produced using the organelle of the host cells
4)
this involved producing copies of viral nucleic acids and proteins to form complementary viruses which are related by lysis of cell.

Question 4

where do virus only replicate

Answer 4

in host cells

Question 5

what is a non specific defence mechanism

Answer 5

-immediate and same for all pathogens
-physical -skin
-phagosytosis

Question 6

what’s a specific defence mechanism

Answer 6

slower and specific to each pathogens

.cell mediated- t lymphocytes
.humoral- b lymphocytes

Question 7

describe phagocytosis

Answer 7

• engulfment and destruction of micro-organisms by pahocytic white blood cells

Question 8

describe the steps of phagocytosis

Answer 8

-phagocyte engulfs the pathogen forming a phagosome

• a lysosome fuses with the phagosome and the lysosomes hydrolyse (break down) the pathogen

insoluble material removed
soluble digested and absorbed

Question 9

what does it mean for a phagocyte to be called a ‘antigen presenting cell’

Answer 9

-phagocyte removes antigen from pathogen they’ve destroyed
- they present the antigen on their cell surface membrane

Question 10

what are the type of specific defence mechanisms

Answer 10

-humoral response - b lymphocytes
-cellular - t lymphocytes

Question 11

what is an antigen

Answer 11

• proteins or glycoproteins that appear foreign to individual organisms
• antigens stimulate production of antibodies by b lymphocytes

Question 12

where may antigens be present

Answer 12

-surface of a pathogen

-cell surface membrane of other organisms

-abnormal body cells

• as a token produced by a pathogen

Question 13

describe the steps of b cells

Answer 13

-each b lymphocyte is capable of producing a different specific antibody

• 1) Secrete small amounts of their specific antibody onto their cell membrane

2) specific antigen attaches as they’re complementary

3) causes b cells to divide by mitosis known as CLONAL SELECTION

4) mitosis results in large quantities of IDENTICAL plasma cells

5) plasma cells produce same specific antibody and secrete into blood

6) some of the b cells are stimulated to divide and develop into memory b cells

Question 14

describe the primary response of an antibody

Answer 14

• slow to produce large conc of antibody

Question 15

describe the secondary response

Answer 15

-if the same antigen is encountered again ,memory b cells divide and create plasma cells

• faster than the primary response and more

-providing immunity as pathogens are destroyed before symptoms develop

Question 16

what is antigenic variation

Answer 16

due to some virus having high mutation rates , leads to some b cells not recognising pathogens so b cells and antigen arnt complementary

Question 17

what do antibodies do and made from

Answer 17

• they’re proteins produced by b lymphocytes

-found in blood plasma, tissue fluid and breast milk

Question 18

describe structure og antibodies

Answer 18

• 4 polypeptide chains
  -2 heavy and 2 light
  -joined by disulphide bonds

each polypeptide chain consist of a constant region and variable region

Question 19

what is the constant region of an antibody

Answer 19

polypeptide chain consist of a constant region

• sequence of amino acids is the same in all molecules of an antibody

Question 20

what is the variable region of an amino acid

Answer 20

the amino acid sequence varies between antibody molecules which are specific to different antigens

Question 21

what do the variable regions of the heavy and light chains form

Answer 21

two antigen binding sites
- they have specific tertiary structures complementary to structure of antigen they attach to to from an antibody antigen complex

Question 22

what to not use when describing antigen binding site

Answer 22

ACTIVE SITE

Question 23

what do antibodies not do

Answer 23

dont directly destroy antigen
- they form antibody antigen complexes that stimulate
phagocytosis
agglutination of antigens

Question 24

what agglutination

Answer 24

-clumping of cells containing the antigen against the specific antibody.

-an antibody can use 2 binding sites to attach to same antigen on 2 diff cells

-this joins cells together . and more antibody attach which destroy easily during phagocytosis

Question 25

what stimulates phagocytosis

Answer 25

phagocytes have receptors in their cell surface membrane that recognise the antibody and enables them to bind and destroy pathogen.

Question 26

describe the t lymphocyte response .

Answer 26

-they DO NOT produce antibodies -they have receptors on their cell surface membrane , binding to specific antigens -1) phagocyte engulfs the pathogen and phagocytoses it 2) phagocyte removes the antigen and paces them on membrane becoming an antigen presenting cell 3)helper T cells with comp receptor protein bind to this antigen 4)this stimulates th cells to divide by mitosis and form genetically identical T cells .

Question 27

what can cloned th cells do

Answer 27

-activate cytoxic T cells which destroy specific foreign cells -develop more helper T cells which stimulate b lymphocytes to divide into plasma cells -develop into memory T cells , which remain in the blood after the infection has cleared to produce a quicker response in the future.