3.2 cells

The structure of eukaryotic cells

1. cell-surface membrane
2. Function of nucleus (containing chromosomes, consisting of protein-bound, linear DNA, and one or more nucleoli)
3. mitochondria
4. chloroplasts (in plants and algae)
5. Golgi apparatus and Golgi vesicles
6. lysosomes (a membrane-bound organelle that releases hydrolytic enzymes)
7. ribosomes
8. rough endoplasmic reticulum and smooth endoplasmic reticulum
9. cell wall with plasmosdesmata (in plants, algae and fungi)
10. cell vacuole (in plants).

Function of cell surface membrane

\~ Regulates the movement of substances in and out of cells

\~ Also Have receptor molecules on the surface so can respond to chemicals like hormones

function of nucleus

* controls cell activity
* controls transcription
* contains instructions to make proteins
* pores allow movement into cytoplasm
* nucleolus makes ribosomes

function of mitochondria

cellular respiration

function of chloroplasts

light dependent photosynthesis

function of golgi apparatus

* Modify, sorts and packages proteins and lipids from the ER for storage in the cell or secretion outside the cell
* makes lysosomes

function of golgi vesicle

Stores lipids and proteins made by the Golgi apparatus and transports them out of the cell.

function of lysosomes

intracellular digestion via lysozymes, digest invading cells or worn out cell components

function of ribosome

site of protein synthesis

function of rough endoplasmic reticulum

Folds and processes proteins that have been made at the ribosomes

function of smooth endoplasmic reticulum

Synthesises and processes lipids

Function of cell wall

Strengthens and protects the cell, prevents shape change

function of vacuole

* Stores materials such as water, salts, proteins and carbs; helps plants support heavy structures like leaves
* maintains pressure and keeps cell rigid, prevent wilting

cell organisation

cell, tissue, organ, organ system, organism

Structure of prokaryotic cells

* Prokaryotic cells are much smaller than eukaryotic cells. They also differ from eukaryotic cells in having:


1. cytoplasm that lacks membrane-bound organelles
2. smaller ribosomes
3. no nucleus; instead they have a single circular DNA molecule that is free in the cytoplasm and is not associated with proteins
4. a cell wall that contains murein, a glycoprotein

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In addition, many prokaryotic cells have:

* one or more plasmids
* a capsule surrounding the cell (protection)
* one or more flagella.

prokaryotic cell replication

\-Binary fission (occurs in bacterial cells): one cell splits in half to become 2 daughter cells

\-the length of time it takes for one bacterial cell to split into two cells is referred to as the organism's generation time. (which varies from 10 mins to hours)

Viruses

* Acellular
* Consist of DNA or RNA core
* Core is surrounded by a protein coat called capsid
* Coat may be enclosed in a lipid envelope
* attachment proteins
* replicate only when they are in a living host cell

Viral Replication

1. Virus attaches to host cell receptor proteins.
2. Genetic material released into host cell.
3. Genetic material and proteins replicated by host cell "machinery".
4. Viral components assemble.
5. Replicated virus released from host cell

Magnification equation

magnification \= image size/actual size

Resolution

the smallest distance by which two objects can be separated and still be distinguished

optical microscope

A microscope that uses visible light and lenses to magnify objects.

electron microscope

* microscope that forms an image by focusing beams of electrons onto a specimen


1. Transmission electron microscope:

* transmit through, can see organelles, 2D
* requires vacuum, thin and dead specimen


2. Scanning electron microscope:

* scan beam of electron across specimen, electrons knocked off specimen
* 3D, can use thick specimens
* lower resolution, dead specimen

Preparing microscope slides

1. Add drop of water to middle of clean slide. Cut onion, Separate into layers.
2. Place the thin tissue onto the water on the slide using tweezers
3. Add drop of iodine solution to act as stain.
4. Place cover tip and put pressure on it to get rid of air bubbles.

Microscope artefacts

Not part of the specimen e.g. air bubbles

cell fractionation

1. Homogenisation: breaking up cells membrane to release organelles, using blender and ice-cold, isotonic, buffer solution.
2. Filtration: remove large cell debris
3. Ultracentrifugation: spins solution at different speeds to separate organelles, heaviest organelle spun out first and forms pellet at bottom of tube whilst leaving the rest of the organelles in the supernatant.

* order: nucleus, chloroplast, mitochondria, lysosomes, ER, ribosomes

Mitosis

1. Interphase: preparation for division so growth and DNA replication occur. G1 (cell grows and new organelles made), S (DNA replicates), G2 ( cells keeps growing and proteins made)
2. Prophase: chromosomes condense, nuclear envelope dissolves and centrioles form
3. Metaphase: chromosomes align along equator and centromere attach to spindle
4. Anaphase: sister chromatids pulled apart to opposite poles as spindles contract
5. Telophase: chromosomes at each end of cell, cell cleavage, nuclear membrane forms again, cytokinesis to produce 2 genetically identical daughter cells

Cancer

mutation in gene causing uncontrolled cell division forming a tumour

cancer treatments

disrupt the cell cycle and kill tumour cells by disrupting G1 phase and S phase to damage DNA and prevent its replication

investigating mitosis

1. cut 1 cm of root tip with scalpel (tip is where growth occurs)
2. boil in hcl for 5 mins
3. remove with tweezers and rinse with cold water and dry on paper towel
4. place on slide and cut 2mm
5. use mounted needle to break tip open and spread the cells flat on a slide
6. add stain to make chromosomes easier to see
7. add coverslip and view with an optical microscope

using optical microscope

1. clip slide onto stage
2. select lowest objective lens
3. use coarse adjustment knob to move stage up
4. look down eyepiece and use coarse adjustment knob until roughly focuses slide
5. use fine adjustment knob till fully clear image
6. to increase magnification, use higher-powered objective lens

Calculating Mitotic Index

cells in mitosis/total number of cells

Calculating actual size of cells

eyepiece graticule and stage micrometer

fluid mosaic model of membrane structure

a model that describes the phospholipid bilayer as fluid and proposes that proteins can be intrinsic such as carrier and channel proteins (allows ions and larger molecules through) or extrinsic such as receptors

phospholipid

A molecule that is a constituent of the inner bilayer of biological membranes, having a polar, hydrophilic head and a nonpolar, hydrophobic tail.

Cholesterol

A lipid that forms an essential component of animal cell membranes and binds to hydrophobic tails causing phospholipids to pack closer together and restrict movement making the membrane less fluid and more rigid.

investigating cell membrane permeability

1. cut 5 equal pieces of beetroot
2. put one of each in a test tube containing 5cm^3 of water
3. set water baths at 10,20,30,40 and 50 degrees for set time
4. removes pieces from tube
5. colorimeter measures how much light is absorbed, use blue filter and distilled water to calibrate it
6. higher absorbance, the more pigment released and the higher the permeability

Movement across membranes

1. simple diffusion (involving limitations imposed by the nature of the phospholipid bilayer)
2. facilitated diffusion (involving the roles of carrier proteins and channel proteins)
3. osmosis (water potential)
4. active transport (involving the role of carrier proteins and the importance of the hydrolysis of ATP)
5. co-transport (illustrated by the absorption of sodium ions and glucose by cells lining the mammalian ileum).

simple diffusion

movement of a solute from an area of high concentration to an area of low concentration

factors affecting simple diffusion

* conc gradient
* thickness of exchange surface
* SA

facilitated diffusion

Movement of specific molecules across cell membranes through protein channels down a concentration gradient.

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* carrier protein: large molecules


1. large molecule attaches to protein
2. protein changes shape
3. releases molecule other side

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* channel protein: charged particles

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calculating rate of diffusion from a curved graph

1. draw tangent
2. calculate gradient = change in y / change in x

Osmosis

Diffusion of water through a selectively permeable membrane from a high to a low water potential

serial dilution

1. line up 5 test tubes
2. add 10cm^3 of intial 2M sucrose solution to first tube and 5cm^3 of distilled water to the other 4
3. use a pipetter, draw 5cm^3 of first solution and add to second and mix
4. repeat process three more times to create solutions of 0.5M, 0.25M and 0.125M

investigating water potential (mass)

1)Prepare sucrose solution of following conc: 0.0M, 0.2M, 0.4M, 0.6M, 0.8M & 1.0M.

2)Use cork borer/ chip to cut potatoes into same sized pieces.

3)Divide chips into groups of 3 & use mass balance to measure mass of each group.

4)Place each group in each solution.

5)Leave chips in solution for a length of time (20mins).

6)Remove chips & pat dry w/ paper towel.

7)Weigh each group & record results

8)Calculate % change in mass for each group & plot graph.

Producing a calibration curve

1. x-axis is concentration of sucrose solution, y-axis is % change in mass
2. plot data
3. draw curve

active transport

Energy-requiring process that moves material across a cell membrane against a concentration difference from low to high.


1. carrier proteins
2. co-transporters: binds to molecules, the concentration gradient of one molecule is used to move the other against its concentration gradient.

* sodium and glucose:


1. sodium actively transported out of cells into blood by SOPI pump
2. sodium diffuses from lumen into cell down concentration gradient with glucose through co-transporter
3. glucose diffuses out into the blood by facilitated diffusion

factors affecting active transport

1. The faster the speed of individual carrier proteins, the faster the rate of active transport.
2. The higher the number of carrier proteins present, the faster the rate of active transport.
3. The faster the rate of respiration and the availability of ATP, the faster the rate of active transport.

Antigen

a toxin or other foreign substance that induces an immune response in the body, especially the production of antibodies.

Pathogen

An organism that causes disease

Phagocytosis

1. phagocyte recognises foreign antigen
2. phagocyte engulfs in phagosome
3. lysosome fuses with phagosome
4. lysozymes released to hydrolyse and kill pathogen
5. phagocyte then present antigen on surface membrane

T cells (cell-mediated immunity)

1. binds to complementary antigens presented on phagocyte
2. activates T-cell
3. T helper cells release chemical signals that activate and stimulate phagocytes and cytotoxic T cells which kill foreign and abnormal cells.
4. activates B cells

B cells (humoral immunity)

* Activated by antigens and by Helper T cell cytokines
* Antibodies on surface bind to complementary antigens
* B cell becomes competent and divides by mitosis to undergo clonal selection
* produce plasma cells and memory cells

plasma cells

* Clone of B cell
* secrete specific antibodies, monoclonal as produced from same B cell
* antibody binds to antigen to form antibody-antigen complex
* leads to agglutination which makes phagocytosis easier

antibody

A protein that acts against a specific antigen

Antibody structure

Two parallel pairs of polypeptide chains;

One pair of heavy chains and One pair of light chains

Each chain contains:


1. constant region
2. Variable region

primary response

first time the immune system combats a particular foreign substance

secondary response

later interactions with the same foreign substance; faster and more effective due to "memory"

active and passive immunity

Active : the immunity that results from the production of antibodies by the immune system in response to the presence of an antigen.

\-natural: catch disease

\-artificial: vaccine

Passive : the short-term immunity that results from the introduction of antibodies from another person or animal.

\-natural: from mother during breast feeding and placenta

\-artificial: injected with antibodies

Vaccines

1. vaccine contains weakened pathogen
2. triggers primary immune response
3. memory cells produced and remain in blood for quick secondary response
4. pathogen destroyed before causes symptoms
5. herd immunity: 90% to protect vulnerable

ethical issues of vaccines

* animal testing
* unknown side effects
* who receives first

antigenic variation

Pathogens alter their surface antigens (and antibodies are rendered ineffective).

Makes vaccine development difficult

Use of monoclonal antibodies

* Monoclonal antibody = antibody produced from a single group of genetically identical B cells
* detect pathogens (ELISA)
* location of cancer cells
* treat cancer
* pregnancy tests

direct ELISA test

1. patient antigens bound to the inside of a well
2. antibody (attached to an enzyme) complimentary to the antigen is added
3. antibody binds to the antigen if present and is immobilised
4. wash out the well to remove unbound antibody
5. add a substrate which reacts with the enzyme to produce a colour change if antibody is still present

Indirect ELISA test

1. patient antigens bound to the inside of a well
2. antibody complimentary to the antigen is added
3. wash out the well to remove unbound antibody
4. second antibody (attached to an enzyme) complimentary to the first antibody is added
5. washed out the well again to remove unbound antibody
6. add a substrate which reacts with the enzyme to produce a colour change if antibody is still present

ethical issues of monoclonal antibodies

\-Production of monoclonal antibodies involves the use of mice, which involves deliberately inducing cancer in mice - people have concerns on the way animals are being used

\-Drug trials can be very dangerous, and have almost killed volunteers in the past - do these drug trials have clear safety guidelines and so forth?

Structure of HIV virus

\-Envelope

\-Attachment proteins

\-capsid

\-RNA

\-reverse transcriptase

HIV replication

1. envelope on virus bind to CD4 on cell surface of helper T cells
2. virus fuses with the cell and releases capsid
3. reverse transcriptase copies the RNA viral into DNA
4. Integrase (viral enzyme) inserts the DNA into the host genome
5. viral proteins produced and assembled into more viruses
6. bud off from the cell to go infect more T cells

AIDS

develops when symptoms of failing immune system show or when helper T cell levels drop below certain level

Why antibiotics are ineffective against viruses

* Antibiotics can't enter human calls - but viruses exists in its host cell
* Viruses don't have own metabolic reactions which antibiotics target
* If we did use them they'd act as a selection pressure + gene mutation = resistant strain of bacteria via natural selection → reducing effectiveness of antibiotics and waste money