bio topic 2

structure of eukaryotic cells

algae cell wall

cellulose

fungi cell wall

chitin

prokaryotic cell structure

always

• cell wall - murein

• cell surface membrane

• circular DNA

• cytoplasm

• 70s ribosomes

sometimes

• capsule - prevent drying eat and attack from host organism cells

• flagellum

how to use eyepiece graticule

TEM

• beam of e- shorter wavelength = > reso

🙂

• > reso

• can observe internal structures (organelles)

☹

• specimens must be very thin

• dead organisms

• lengthy preparation time → artefacts

• B&W

How to use microscope to observe x in cells using optical microscope

1. Add drop of water to glass side

2. Obtain thin section of plant tissue and place on slide

3. Stain with iodine in KI

4. Lower cover slip using mounted needle

SEM

🙂

• can produce 3D images

• can be used on thick/ 3D specimens

• allow external 3D structure of specimens to be observed

☹

• <reso

• cannot observe live specimen

• B&W

cell fractionation + ultracentrifugation

A) homogenisation using cold, isotonic, buffered solution

= breaking up cells

1. ice cold: prevent enzyme activity

2. isotonic: prevent lysis

3. buffer: prevent denaturing enzyme/ protein

B) filtration

C) ultracentrifugation

• centrifuge at low speed and remove supernatant

• centrifuge at higher speed

• pellet settles at bottom, supernatant = solution

measuring cells

epg and micrometre

interphase

1. G1:growth

   1. cells make RNA, enzymes and proteins for growth

2. S: DNA in nucleus replicates

   1. each chromosome = 2 sister chromatids

   2. DNA synthesis

3. G2: cell continues to grow, check and repair errors

mitosis

*after interphase, before prophase, human cell nucleus contains 92 DNA molecules

1. prophase

   1. chromosomes condense and now visible when stained

   2. nuclear envelope breaks down

2. metaphase

   1. chromosomes line up on equator

   2. spindle fibres reach to chromosomes and attach to centromeres

3. anaphase

   1. sister chromatids separate at centromere and pulled to opp poles by spindle fibres

   2. spindle fibres shorten

4. telophase

   1. chromosomes arrive at opp poles and begin to decondense

   2. nuclear envelope and nucleolus begin to reform

   3. spindle fibres break down

5. cytokinesis

   1. (cell plate)/ (cleavage furrow)

binary fission

1. single, circular DNA replicates

2. plasmids replicate

3. parent cell divides into 2 cells, with cytoplasm roughly halved between 2 daughter cells

4. 2 daughter cells each contain single copy of circular DNA and variable no. of plasmids

5. new cell walls formed

fluid mosaic model

fluid = phospholipids and proteins can move

• phospholipids mainly move sideways, within own layer

mosaic = various proteins embedded

purpose of phospholipid bilayer

1. compartmentalisation for metabolic reactions (diff conditions)

2. permeability

phospholipids

• hydrophilic/ polar phosphate heads

  • attracted to water

  • orientate outwards

• hydrophobic/ non-polar fatty acid tails

  • repelled from water

  • orientate towards interior

• Water present inside and outside cell

intrinsic/ integral proteins

• span entire membrane

• protein channels = water-filled tubes to allow water-soluble ions to diffuse across membrane

• carrier proteins

  • bind ions/ molecules and change shape to move molecules across membrane

extrinsic proteins

• mechanical support

• or in conjunction with glycolipids and act as cell receptors

• (proteins help cells adhere to each other)

cholesterol

• stabilise membrane

• rigidity

• restricts movement of fatty acid tails

  • < mov = < permeable = < leakage

glycoproteins and glycolipids

• cell surface receptors

• cell-to-cell recognition

• receptors in cell adhesion and stabilisation

RP4 factors affecting membrane fluidity

ethanol → dissolves phospholipid bilayer

acid → alter membrane proteins

high temp → denature membrane proteins

diffusion

• passive

• dynamic equilibrium

• no net mov

• small, non-polar substances

factors affecting diffusion rate

• conc grad

• temp

• SA

• diffusion distance

• properties of molecules/ ions

facilitated diffusion

• for charged, large, polar molecules

• passive

• channel proteins

• carrier proteins

• proteins limiting

osmosis

• no net mov

• dynamic equilibrium

• hypertonic, isotonic, hypotonic

  • animal: cell crenation, cell lysis

  • plant: cell plasmolysis, turgid

active transport

• molecules and ions using ATP and carrier proteins

• ATP + H2O → ADP + Pi + energy

  • reversible

  • condensation/ hydrolysis

  • ATP hydrolase or ATP synthase (phosphorylation)

co-transport

 

Types of cells that stimulate immune response (presence of antigens)

• cells from other organism of same species

• Abnormal body cells

• pathogens

• Toxins

antigen

• Foreign protein molecule on surface that stimulates an immune response

• Allows cell recognition

phagocytosis

1. Phagocyte (has specific surface cell receptor) attaches themselves to surface of pathogen

2. Phagocyte engulfs the pathogen to form phagosome

3. Lysosome moves towards and fuses with the phagosome

4. Lysosome releases lysosomes which digest/destroy the pathogen

5. Soluble products from breakdown of pathogen absorbed into cytoplasm of phagocyte

6. Antigens from bacteria presented/displayed on phagocyte cell surface membrane

antibody

Protein that is specific to the antigen and is secreted by plasma cells/ produced by B cells

mAB

• Same tertiary structure

• AB produced from identical plasma cells

antigen variability

• Mutation in viral DNA

• Altered tertiary structure of attachment protein

• Allows attachment protein to bind to different receptors

purpose of disulfide bridge

join 2 diff polypeptides

How can determining the genome of the viruses allow scientists to develop a vaccine

• Scientists could identify proteins that derive from the genetic code

• And so identify potential antigens to use in the vaccine

How vaccination leads to protection against disease

• Humoral response etc. or:

1. Vaccine contains antigen from pathogen

2. Phagocyte APC on surface

3. TH cell complementary receptor protein binds to antigen

4. TH cell stimulates B cell (with complementary AB on surface)

5. B cell divides to form clones all secreting same AB (large amounts)

active immunity

• Memory cells

• Produce AB by plasma cells

• Long term as AB produced in response to antigen

• Take time to develop

passive immunity

• No memory cells

• AB introduced form external source e.g. vaccine

• Short term as AB given is broken down

• Fast acting

Why percentage of population vaccinated doesn't need to be 100% to be effective in preventing spread of disease

• More People immune

• Unvaccinated less likely to contact infected

OTHERS

Why use > 1 antibiotic (using knowledge of evolution of antibiotic resistance in bacteria)

• Some bacteria resistant to new/ old bacteria

• Resistant bacteria will reproduce to produce > resistant bacteria

• Use of both = one antibiotic will kill bacteria resistant to other antibiotic

  • Unlikely that bacteria resistant to both new and old antibiotic

  • Use of both antibiotics likely to kill all/ most bacteria

secondary immune response

• When encounter same pathogen

• Faster and > production of ABs

• Memory cells divide quickly to form plasma cells

B cell humoral response

1. B cell ABs bind to viral complementary antigens

2. B cell presents antigens on cell surface membrane

3. TH cells stimulate B cells to divide by mitosis to produce clones

4. Differentiate into B plasma cells and B memory cells

5. Plasma cells secrete ABs which bind to antigen

6. Memory cells involved in secondary immune response

why T cells effective against viruses

• Destroy virus infected cells

• Viruses need living cells to reproduce

T cell mediated response

1. Phagocytosis

2. Phagocyte engulfs pathogen and presents antigens on cell surface membrane

3. TH cell with complementary receptors bind to antigens, activating TH cell to divide rapidly by mitosis and form clones (clonal expansion)

4. Cloned T cells either

   1. Stimulate B cells to divide and secrete their AB

   2. Stimulate phagocytes to carry out phagocytosis

   3. Develop into T memory cells

   4. Cytotoxic T cells (release perforins which punch holes into cell surface membranes, cell becomes freely permeable and dies

ELISA

1. Antigens bound to bottom of reaction vessel

2. Blood sample of patient added, AB present bind to antigen (primary AB)

3. Washed out (so that no excess AB's are left to cause false positive?)

4. Secondary ABs added + enzyme

5. Washed out to prevent false positives

6. Solution added with substrate

7. Substrate reacts with enzyme and colour changes = positive test

Role of AB in stimulating phagocytosis

• Agglutination (clumping) so more easily located and engulfed by phagocytes as less spread out in blood

• Act as markers for phagocytes

How HIV affects production of AB when AIDS develops

• HIV destroys TH cells

• So can't stimulate cell division of B cells to produce clones

• So less ABs produced

Why virus can be described as inactive

• No more cells infected

• Virus not replicating

replication of HIV

1. Attachment proteins on HIV binds to CD4 protein on TH cells

2. Capsid fuses to cell membrane, RNA inserted into cell

3. Reverse transcriptase converts RNA to DNA

4. DNA inserted into TH cell DNA

5. TH produces mRNA and viral protein (DNA transcribed into mRNA, mRNA translated into viral protein)

• Viral proteins assemble to form new virus particles

• Viral particles released from cell, producing lipid envelope from cell membrane

antibody structure

• variable region

• 4 polypeptide chains joined by disulfide bridge

• constant region

• 2 binding sites so can bind to >1 bacterium/ virus at same time

• heavy chain and light chain

function of golgi apparatus

• Modify/ package/ transport proteins

  • Make/ transport glycoproteins

• Modify/ package/ transport lipids

  • Make/ transport glycolipids

• Forms/ release vesicles

why antibiotics not effective against viruses

• No enzymes

• No metabolic processes

• No cell wall/ murein