chapter 2 summary

structure of the nucleus

1. surrounded by nuclear envelope (double membrane)
- the nuclear envelope contains many pores

2. granular, jelly-like substance inside the nucleus called nucleoplasm

3. contains chromosomes which are made from protein-bound, linear DNA

4. contains nucleolus which is a small sphere inside the nucleus:
- is the site of rRNA production
- makes ribosomes

function of nucleus

1. DNA replication and transcription site (mRNA)
2. contains genetic info
3. controls cell's activity

structure of smooth endoplasmic reticulum

1. has a folded membrane called cisternae
2. does NOT have ribosomes

function of smooth endoplasmic reticulum

Synthesises, processes, stores and transports lipids and carbohydrates

Structure of rough endoplasmic reticulum

1. has a folded membrane called cisternae
2. has ribosomes on the cisternae

function of rough endoplasmic reticulum

1. provides large SA for protein and glycoprotein synthesis
2. folds and processes proteins that have been made at the ribosomes (protein synthesis)

Structure of Golgi Apparatus

1. fluid-filled, membrane-bound flattened sacs (cisternae)

2. small, rounded, hollow structures called vesicles

Function of Golgi Apparatus

1. processes and packages lipids and proteins
2. makes lysosomes
3. produces secretory enzymes

structure of golgi vesicles

1. fluid-filled sac in the cytoplasm
2. produced by golgi apparatus
3. surrounded by a membrane

function of golgi vesicles

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

structure of lyozomes

1. a round organelles surrounded by a membrane
- no clear internal structure
2. a type of golgi vesicle
3. contains digestive enzymes called LYZOSYMES

function of lyosome

1. hydrolyses phagocytosis
2. autolysis (breaks down dead cells)
3. exocytosis (releases enzymes to outside cells to destroy materials)
4. digests/breaks down worn-out components of the cell for the re-use of the material

structure of mitochondria

1. oval shaped
2. double membrane
- inner membrane folded to form cristae
3. has a fluid centre called mitochondrial matrix
- contains enzymes involved in respiration
4. loop of mitochondrial DNA

function of mitochondria

1. site of aerobic respiration
2. site of ATP production
3. contains DNA to code for the enzymes needed in respiration

structure of ribosomes

1. very small organelle
either:
- floats freely in the cytoplasm
- is attached to RER

2. made up of 2 sub-units:
1. rRNA
2. Protein

3. NOT surrounded by a membrane

function of ribosomes

site of protein synthesis via translation:
- large sub-unit joins amino acids
- small subunit contains mRNA binding site

structure of vacuole

1. membrane-bound organelle found in the cytoplasm of plant cells
2. contains cell sap (weak solution of sugars and salts)
3. surrounded by membrane called tonoplast

function of vacuole

1. helps maintain pressure inside of cell and keep cell turgid/rigid
2. provides support and prevents plant from wilting
3. temporary store of amino acids and sugars
4. involved in the isolation of unwanted chemicals in the cells
5. the pigment could colour petals, which would attract pollinators

structure of chloroplast

1. small flattened structure
- found in plants and algal cells
2. surrounded by a double membrane
3. contains thykaloids (folded membranes embedded with pigment)
- thykaloids stack up to from grana
- grana are linked together by lamellae (thin flat peices of thykaloids)
4. fluid-filled stroma that contains enzymes for photosynthesis

function of chloroplast

Site of photosynthesis

structure of cell wall in plants and fungi

in plants:
1. made of microfibrils of cellulose polymer

in fungi:
1. made of chitin

function of cell wall

1. provides structural strength to the plant
2. prevents cell from changing shape

explain the role of cholesterol, glycoproteins and glycolipids in the cell-surface membrane

1. cholesterol: steroid molecule that connects phospholipids and reduces fluidity

2. glycoproteins: cell signalling, cell recognition and binding cells together

3. glycolipids: cell signalling and cell recognition

cell wall in prokaryotic cells

1. made of murein
- a glycoprotein

supports the cell

capsule in prokaryotic cells

only in some prokaryotes (e.g. bacteria)

made of secreted slime and helps prevent bacteria from attack by immune system cells

circular DNA in prokaryotic cells

1. floats freely in the cytoplasm
2. one long coiled-up strand
3. not attached to any histone proteins

plasmids in prokaryotic cells

1. small loops of DNA
- not part of the main circular DNA
2. contains genes for things like anti-biotic resistance

viral replication

1. attachment proteins attach to receptors

2. viral nucleic acid enters cell

3. reverse transcriptase makes DNA from RNA

4. virus assembled and released from cell

describe how prokaryotic cells replicate by binary fission

1. replication of circular DNA and plasmids

2. division of cytoplasm to produce 2 daughter cells, each with a single copy of circular DNA and a variable number of plasmids

Outline the role of organelles in the production, transport and release of proteins from eukaryotic cells

1. DNA in nucleus is the code for protein
2. Ribosomes produce protein
3. Golgi apparatus modifies proteins
4. Vesicles transprts protein

Name an organelle found in both a chloroplast and a prokaryotic cell.

ribosome

The detail shown in the diagram above would not be seenu using an optical microscope.
Explain why.

B/c optical microscopes have low resolution
- light has a longer wavelength

The cell surface membrane can be seen with a transmission electron microscope but not with an optical microscope.
Explain why.

Electron microscope has higher resolution (than optical microscope);

Before the cell was examined using the electron microscope, it was stained. This stain caused parts of the structure of the cell-surface membrane to appear as two dark lines.
Suggest an explanation for the appearance of the cell-surface membrane as two dark lines.

1. Membrane has phospholipid bilayer
2. Stain binds to phosphate / glycerol
3. On inside and outside of membrane.

Contrast how an optical microscope and a transmission electron microscope work and contrast the limitations of their use when studying cells.

1. TEM use electrons and optical use light

2. TEM allows a greater resolution

   • So with TEM smaller organelles can be seen and in greater detail

3. TEM view only dead specimens and optical can view live specimens

4. TEM does not show colour but optical can

5. TEM requires thinner specimens

6. TEM requires a more complex and time consuming preparation

7. TEM focuses using magnets and optical uses lenses

Describe how you could make a temporary mount of a piece of plant tissue to observe the position of starch grains in the cells when using an optical microscope.

Add a drop of water to a glass slide;
Obtain thin section of plant tissue and place on slide;
Stain with potassium iodide;
Lower cover slip using mounted needle

The scientists used an optical microscope to measure the number of capillaries in thin sections cut from samples of heart muscle.

Describe the method they would have used to find the mean number of capillaries per mm2.

• measure diameter of the field of view and calculate the area

• Use the micrometer slide and eyepiece graticule

• Select fields of view randomly

• Count the number of capillaries in a large number of fields of view and calculate the mean

mitotic index

number of cells undergoing mitosis ÷ total number of cells

how to calculate the numbers of minutes a cell spends in a particular phase of the cell cycle

(number of cells in that cell cycle ÷ total number of cells) × number of minutes spent in that particular phase of the cell cycle

explain why the tip of the root is used

because the cells in the tip of the root are actively dividing (by mitosis)

explain the purpose of incubating the root tip with hydrochloric acid

• stops cell division from occurring

• hydrolyses the middle of the lamella so that the cells can be seperated easily

describe why a stain is used

the stain binds to the chromosomes so that they become visible

describe how you would count the cells to ensure mitotic index is accurate

• examine a large field of view to ensure a representative sample size

• count only whole cells, to standardise counting

optical microscopes

1. uses light

2. lower resolution

3. can view live specimens

4. can show colour

5. smaller structures not visible

6. focused using glass lenses

electron microscopes

• uses beam of electrons

• higher resolution

• can only view dead specimens

• cant show colour

• smaller structures visible

• focused using magnets

describe TEMs (transmission electron microscopes)

1. higher resolution

2. produces image of internal structure (e.g. organelle structure)

3. produces 2D images

4. requires thinner specimen

describe SEMs (scanning electron microscope)

1. lower resolution

2. produces images of external structures only

3. produces 3D images

4. can use thicker specimens

How do you calibrate an eyepiece graticule?

1. place stage micrometer on the stage of the microscope

2. align the scales of the eye piece graticule and stage micrometer whilst looking through the eyepiece

3. count the number of eyepiece graticule divisions that fit into one division on the stage micrometer

   • divide the length of one micrometer by this answer

outline how a student could prepare a temporary mount of tissue for an optical microscope

1. add drop of water to glass slide

2. obtain thin section of plant tissue and place on the slide

3. stain with potassium iodide

4. lower cover slip using mounted needle

explain why fractionated cells are kept in a cold, buffered, isotonic solution

1. cold: to reduce the activity of enzymes that break down organelles

2. buffered: maintains pH to prevent damage to organelles and to prevent enzymes denaturing

3. isotonic: organelles must be the same water potential as the solution to prevent osmosis

   • osmosis could cause the organelles to shrivel or burst

describe what happens during cell fractionation

homogenisation

• cells broken open in cold, buffered, isotonic solution by using a blender or by crushing them

filtration

• solution is filtered through a gauze to remove large cells/ tissue debris

ultracentrifugation

• filtered solution is spun at high speed in centrifuge

  • this separates organelles according to their density

• this process is repeated several times at increasing speeds

• remove supernatant and leave behind pellet

State the order of sedimentation of organelles during differential centrifugation.

most dense to least dense:

1. nucleus

2. mitochondria

3. lysosomes

4. RER

5. plasma membrane

6. SER

7. ribosomes

Define simple diffusion

• movement of small, lipid-soluble, non-polar molecules, through a partially-permeable membrane, down a concentration gradient

• passive process

Define facilitated diffusion

• movement of molecules down a concentration gradient via channel (or carrier) proteins

• passive process

Active transport

• movement of molecules against a concentration gradient via a carrier protein

  • using ATP

• active process

co-transport

movement of 2 different substances using a carrier protein

contrast active transport and facilitated diffusion

• facilitated diffusion is passive but active transport is active (requires ATP)

• facilitated diffusion involves either channel or carrier proteins, whereas active transport only involves carrier proteins

• facilitated diffusion takes place down a concentration gradient but active transport can occur against a concentration gradient

compare and contrast how water and inorganic ions enter cells

• both move down concentration gradient

• both move through protein channel in membrane

• ions can move against a concentration gradient by active transport

Features of a cell specialised for absorption

1. Large number of mitochondria

   • to release energy for AT in the form of ATP

2. Large number of channel and carrier proteins

   • for facilitated diffusion

3. folded membrane

   • so large SA

Describe how a carrier protein could facilitate the diffusion of a glucose molecule across a cell membrane

• the glucose molecule attaches to the carrier protein

• The carrier protein then changes shape and releases the glucose molecule on the opposite side of the membrane

How the movement of Na+ molecules out of the cell allows for the absorption of glucose into the cell

1. The movement of Na+ out of the cell maintains a concentration gradient

2. Na+ moving in by co-transport

- bringing glucose with it

How the movement of substances is affected by membrane structure

1. Phospholipid bilayer allows for the movement of non-polar substances

2. Phospholipid bilayer prevents movement of polar substances

3. Carrier proteins allow active transport and co-transport

4. Channel proteins allow facilitated diffusion

5. Shape of proteins channel and carriers determines how much movement

6. No. of proteins channels and carriers determines how much movement

7. Membrane SA determines how much movement

8. Cholesterol affects fluidity/permeability

Osmosis definition

Movement of water molecules down a water potential gradient

explain why the cell cycle does not occur in some cells

after differentiation some types of cells no longer have the ability to divide

describe what happens in interphase

G1:

- cell grows and doubles in size

- organelles double and proteins are made

S:

- DNA is replicated

G2:

- cells keep growing and proteins are made for cell division

- DNA is checked for errors e.g mutation

stages of mitosis

1. prophase

   • chromosomes condense and become visible

   • centrioles seperate

   • nuclear envelope breaks down

2. metaphase

   • chromosomes align along equator of cell

   • spindle fibres released and attached to chromatid by centriole

3. anaphase

   • spindle fibres retract and pull centromere and chromatid towards opposite poles

   • centromere divides into 2

   • individual chromatids are pulled to each opposite pole

4. telophase

   • chromosomes are now at each pole in the cell

   • chromosomes become longer and thinner again

   • spindle fibres disintegrate

   • nucleus starts to reform

   • cytoplasm divides into 2 (cytokinesis)

antigen

foreign protein/molecule that stimulates an immune response

Give 2 ways in which pathogens can cause disease

1.release toxins

2.kill cells

4 things antigens are used to identify

1. pathogens

2. toxins

3. abnormal body cells

4. cells from organisms of the same species

if physical barriers fail, what is the next line of defence in an organism?

phagocytosis

antibodies

a protein specific to an antigen produced by B cells

explain the structure of an antibody

1. 4 polypeptide chains

   • 2 heavy chains and 2 light chains

2. variable region

   • contains specific binding site

3. generic constant region

   • allows attachment to phagocytic cells

4. hinge

   • allows for flexibility

   • hence can bind to multiple antigens

antibody diagram

antigen-antibody complex

what is the role of the disulfide bridge in forming the quaternary structure of an antibody

joins 2 polypeptides

role of antibodies in stimulating phagocytosis

antibodies bind to antigens and cause agglutination

• cells clump together and makes it easier for phagocytes to locate them

serve as markers

• stimulates phagocytes to engulf cells

explain why antibodies are only effective against a specific pathogen

• antigens have a specific tertiary 3D structure

• shape of the antibody is complementary to the antigen

• antibody binds to the antigen, forming an antibody-antigen complex

state how antibodies deal with infections via neutralisation

antibodies bind to toxins and prevents the binding of these toxins to the host cells

monoclonal antibody

an antibody produced from identical B cells

give one example of using monoclonal antibodies in medical treatment

carries medicine to specific cells

describe 3 ethical considerations in the use of monoclonal antibodies

1. animal testing

- involves use of mice in antibody production

2. informed consent

- patients must know all the benefits + risks of the drugs

3. drug trials

- testing on volunteers can be dangerous

- there can be issues over trial conduct

positive result in ELISA test

1. The first antibody binds to complementary antigen

2. A second antibody with enzyme attached is added

3. The second antibody attaches to the first antibody

4. Solution containing substrate is added and colour changes

phagocytosis

1. A phagocyte recognises a foreign antigen on a pathogen and moves towards pathogen via chemotaxis

2. pathogen is engulfed (via endocytosis) and enclosed in vacuole/phagosome

3. vacuole/phagosome fuses with lysosome, forming phagolysosome

4. lysosome contains enzyme called lysozyme

5. pathogen destroyed by lysozymes

6. phagocyte absorbs the products from pathogen hydrolysis

7. phagocyte presents the pathogens antigens

   • antigens from pathogens are displayed on cell surface membrane

in what case is an immune response disadvantageous

in organ transplants:

- immune system recognises the organ as 'non-self' and attempts to destroy it

how do doctors minimise the risk of organ rejection?

1. tissue type is matched

2. immunosuppressants are used

outline the process of the cell-mediated/cellular immune response?

1. complementary helper T cells bind to foreign antigen on antigen-presenting cell

2. releases cytokines

3. Helper T cells divide by mitosis (clonal expansion of complementary T helper cells)

- become memory cells or trigger humoral response

4. clonal expansion of cytotoxic T cells (TC)

How do Cytoxic T cells kill infected cells?

by producing an enzyme called perforin that makes holes in the cell surface membrane

describe the steps in the humoral response

1. B cells bind to complementary antigen

2. B cells divide via mitosis to produce plasma cells

3. plasma cells produce and secrete specific antibodies that are complementary to the antigen

4. some B cells develop into memory cells

- circulate the blood

- secondary response

in what cases may reinfection of the same pathogen occur?

1. different strains of the same pathogen

2. antigenic variability (different antigens)

3. when memory cells arent useful and produce an incorrectly shaped antibody

what is antigenic variation and what are its consequences?

When pathogens change their surface antigens

• The immune system cannot recognise this new antigen, so the memory cells don’t recognise it

• So a primary response must occur, which takes time and gives the individual symptoms

How do countries combat antigen variation

1. New vaccines are developed and chosen each year

2. Governments and health authorities have vaccinator programmes for the most effective vaccine that year

what are 2 issues with taking a vaccine orally?

1. there are enzymes in the gut that may break down the oral tablet

2. the molecules of the vaccine could be too large to be absorbed into the gut

Explain why antibiotics are ineffective against viruses

1. antibiotics work by preventing bacteria from making normal cell walls

   • but viruses rely on host cells for metabolic activities

2. viruses have a protein coat

   • so they dont have sites where the antibiotics can work

Describe how vaccines can lead to the production of antibodies against a disease-causing organism.

1. Vaccine contains antigen from pathogen

2. Macrophage presents antigen on its surface

3. T cell with complementary receptor protein binds to antigen

4. T cell stimulates B cell

5. B cell secrets large amounts of antibody

Why may vaccination not eliminate a disease?

1. fails to induce immunity in some people

2. vaccinated people may harbour the pathogen and infect others

3. antigenic variability (where antigens change frequently)

4. varieties of pathogen/strains

5. some pathogens 'hide' from the bodys immune system

6. medical/religious/ethical objections to taking the vaccine

what is herd immunity?

When a sufficiently large proportion of the population has been vaccinated to make it difficult for a pathogen to spread within that population

Why is herd immunity important?

its impossible to vaccinate everyone

- due to religious/medical/ethical objections

state some ethical issues with vaccinations

1. animal testing

2. side effects

3. vaccination testing

4. trialling new vaccines with unknown health risks

5. herd immunity

- should we make vaccines compulsory

6. balancing individual risk and community risk

Describe the difference between active and passive immunity.

1. Active involves memory cells, passive does not

2. Active involves production of antibody by plasma cells / memory cells

3. Passive involves antibody introduced into body from outside

4. Active long term, because antibody produced in response to antigen

5. Passive short term, because antibody is broken down

6. Active takes time to work, passive fast acting

Describe the structure of HIV

1. lipid envelope + attachment proteins embedded

2. Capsid encloses 2 single RNA strands + enzymes including reverse transcriptase

3. Its a retrovirus bc it contains RNA