2.1 Cell Structure

structure of a eukaryotic cell

Large and have a nucleus bonded by nuclear membranes (nuclear envelope), dna associated with histone proteins, membrane bound organelles, 80s ribosomes

Animal and plant cells.

Nucleus

Found in eukaryotic cells

structure- nuclear envelope and pores. chromatin. nucleolus

Function- stores genetic material for polypeptide production. dna replication. production of mrna

structure of prokaryotic cells

Small, lack nucleus, 70s ribosomes, plasmids may be present, cell wall made of murien. No membrane bound organelles

differences between eukaryotic and prokaryotic cells

80s vs 70s ribosomes, membrane/ no membrane bound organelles, no plasmids/ possible plasmids

structure of virus particles

genetic material, capsid and attachment proteins

role of capsid and attachment protein

Capsid- helps to protect the virus from the host's immune system and to deliver the viral genetic material into the host cell.

Attachment proteins- bind to host cells in order to infect them.

why are viruses described as acellular and non - living

• no cell surface membrane

• non-living, have no metabolic reactions

• can not respire / replicate

• no nutrition

relate the structure of of a virus to its replication in cells

a virus uses attachment proteins on its surface to bind to complementary receptor proteins on the surface of a host cell. The virus then injects its DNA or RNA into the host cell. The host cell then uses its nucleic acid and protein-building machinery (ribosomes) to produce new viral particles.

how does an optical microscope work

1. Visible light passes through the specimen and is bent through the lens system

2. This creates a magnified image

3. The lenses in the microscope magnify the image by refracting the light and the focussing knobs are used to focus the light on the retina

limitations of an optical microscope

Advantages: minimal preparation

Disadvantages: low resolution because long wavelength

how does a transmission electron microscope work

1. Prepare a thin slice of specimen & place in vacuum chamber

2. Fire an electron beam down through the specimen from a giant gun

3. An electromagnetic coil (first lense) concentrates the electrons into a more powerful beam.

4. Another (second lense) focuses the bean onto a certain part of the specimen.

5. The beam passes through the specimen and pick up an image of it

6. The projector lense magnifies

7. Image becomes visible when beam hits fluorescent screen.

8. Image can be viewed directly through viewing portal, binoculars at the side or on a tv monitor

Specimen is treated with heavy metals

advantages and limitations of a transmission microscope

Advantages: High resolution, living organisms can be viewed

Disadvantages: expensive, 2D image

how does a scanning electron microscope work

1. Electron gun shoots electron beam down at the specimen

2. A positively charged electrode (anode) attracts the electrons and accelerates them into an energetic beam

3. An electromagnetic coil brings down the electron beam to a very precise focus, much like a lense

4. Another coil lower down steers the beam from side to side

5. The beam systematically scans across the object being viewed

6. Electrons of the beam hit the surface of the object and bounce off it

7. A detector registers these scattered electrons and turns them into a picture

8. A highly magnified image of the object is displayed on a tv screen

advantages and limitations of a scanning electron microscope

Advantages: high resolution, 3D image, can contain artefacts

Disadvantage: can’t observe living specimens, expensive, size

difference between magnification and resolution

Magnification: This tells you how many times bigger the image is than real life.

Resolution: The ability to see two structures very close together as separate structures.

process of homogenisation

1. sample tissue must be placed in cold isotonic buffered solution. cold- reduce enzyme activity. isotonic-prevent osmosis. buffered- prevent enzymes denaturing

2. the solution is then homogenised using a homogeniser, breaking plasma membrane and releasing organelles into a solution called homogenate

3. the homogenate goes through filtration- filtering out large debris leaving filtrate

ultra-centrifugation

1. filtrate is placed into the centrifuge

2. first spun at a low speed for a long period of time causing the heaviest organelles to settle at the bottom. this called the pellect

3. other organelles stay suspended in the solution above the pellet

4. this solution is also known as the supernatant

5. supernatent is placed in another tube and span at a faster speed for a shorter amount of time

organelle order of mass

• nucleaus

• chloroplast

• mitochondria

• lysosomes

• endoplasmic reticulum

• ribosomes

Mitochondria

Found in eukaryotic cells

Surrounded by a double membrane, inside is a fluid matrix containing ribosomes and a loop of DNA

Function- Produce ATP during aerobic respiration

Rough Endoplasmic Reticulum (RER)

Found in eukaryotic cells

Consists of a series of flattened membranes bounds sacs (cisternae) that are linked to the nuclear envelope. This type of ER has ribosomes studded into its membranes

Site of protein synthesis and used a transport system for proteins

Chloroplast

Found in eukaryotic cells

Large organelle surrounded by a double membrane. Contains a gel-like fluid called the strong and internal membranes called thylakoids: these contain chlorophyll

function- site of photosynthesis

Cell Wall

Found in eukaryotic and prokaryotic cells

In plants it is made of cellulose. In prokaryotic cells it is made of murein. These structures also have pores called plasmodesmata, that allow the cytoplasm of adjacent cells to connect.

function- supports herbaceous plants and acts as a temporary food store.

Golgi Apparatus

Found in eukaryotic cells

A crescent shaped stack of flattened membrane bound sacs called cisternae, vesicles

Function- chemically modifying & packaging proteins and lipids to be exported from the cell

• forms vesicles and lysosomes

Smooth Endoplasmic Recticulum

Found in eukaryotic cells

Consists of a series of flattened, membrane bound sacs (cisternae) that are linked to the nuclear envelope.

Function- synthesises, stores and transports lipids and carbohydrates

Ribosomes

Found in eukaryotic (80s) and prokaryotic (70s) cells

Made of a type of RNA and protein. Consists of a large subunit and a small subunit

Function- site of protein synthesis

Lysosome

Found in eukaryotic cells

Consists of a lumen, surrounded by a single membrane and contains hydrologic enzymes.

Function: Digests unwanted material in the cell

Vacuole

Found in prokaryotic and eukaryotic cells

A single membrane called a tonoplast, containing a solution of mineral salts, sugars, amino acids, wastes and sometimes pigments

Function- provides mechanical strength and support. Stops the cell bursting in dilute solution I.e prevents osmotic lysis

Describe the role of plasmids, capsules and flagella.

Plasmids- replicate and move between cells so that genetic information can be shared.

Capsule- Protective slimy layer which helps the cell to retain moisture and adhere to surfaces

Flagella- help the cell move

tem vs optical

TEM use electrons and optical use light;

2. TEM allows a greater resolution

3. (So with TEM) smaller organelles/named cell structure can be observed OR greater detail in organelles/named cell structure can be observed

4. TEM view only dead/dehydrated specimens and optical (can) view live specimens

5. TEM does not show colour and optical (can);

6. TEM requires thinner specimens

7. TEM requires a more complex/time consuming preparation

8. TEM focuses using magnets and optical uses (glass) lenses