2.1.1 cell structure

Question 1

State the types of microscopes

Answer 1

Light microscope
Electron microscope
Transmission electron microscope (TEM)
Scanning electron microscope (SEM)
Light scanning confocal microscope

Question 2

State and describe the different ways to prepare a sample

Answer 2

Dry mount - Used with solid specimens that are either whole or sectioned (sectioning - cut into very thin slices with a sharp blade). E.g. hair, pollen, dust, and insect parts
Specimen placed centre of slide and cover slip placed on top of specimen.
Wet mount - specimen suspended in a liquid such as water or an immersion oil. Cover slip is placed at an angle. E.g. aquatic samples or other living organisms.
Squash slides - used for soft samples e.g. root tip squashes used to look at cell division. Wet mount is first prepared and then a lens tissue is used to gently press down the cover slip. Warning: damage can be done to cover slip (can break)
Smear slides - the edge of the slide is used to smear the sample across another slide creating a thin even coating. Cover slip placed over. E.g. a sample of blood.

Question 3

Why would you stain a cell?

Answer 3

Stains increase contrast as different components within a cell take up the stains to different degrees.
The increase in contrast allows components to become visible so they can be identified.

Question 4

Define differential staining

Answer 4

Differential staining can distinguish between two types of organisms that would otherwise be hard to identify. (can also differentiate between different organelles of a single organism)

Question 5

State the different staining techniques

Answer 5

Negative stain technique
Gram stain technique
Acid-fast technique

Question 6

Describe negative stain technique

Answer 6

Positively charged dyes (i.e. Crystal violet or methylene blue) are attracted to negatively charged materials in cytoplasm leading to staining of cell components.
Negatively charged dyes (i.e. nigrosin or Congo red) are repelled by the negatively charged cytosol. This means that the dye stays outside of the cell (leaving the cells unstained) causing the cells to stand out against the stained background. This technique is called a negative stain technique.

Question 7

Describe Gram stain technique

Answer 7

A technique used to separate bacteria into two groups, Gram-positive bacteria (e.g Streptococcus pneumonae - causes pneumonia) and Gram-negative bacteria (e.g. Yersinia pestis - causes bubonic plague).

Crystal violet is first applied to a bacterial specimen, then iodine, which fixes the dye. Slide then washed with alcohol. Gram-positive bacteria retain the dye where as Gram-negative bacteria have much thinner walls and lose the stain.
Gram-negative bacteria are stained with the counterstain safranin, which makes them appear red.

Question 8

Describe acid-fast technique

Answer 8

The technique differentiates species of Mycobacterium from other bacteria.
Heat or a lipid solvent is used to carry the first stain, carbolfuchsin, into the cells. Then the cells are washed with a dilute acid-alcohol solution. Mycobacterium species resist the effect of the acid-alcohol and retain the carbolfuchsin stain (bright red). Other bacteria lose the stain and take on the subsequent methylene blue stain (blue). Thus the acid-fast bacteria appear bright red, while the nonacid-fast bacteria appear blue when observed under oil-immersion microscopy.

Question 9

Difference between Light, electron and confocal scanning laser microscopes

Answer 9

Light:
Magnification: x1500	
Resolution: 200nm
Cost: inexpensive 
Uses: Thin, transparent samples (living or dead); Natural colour; Simple preparation

SEM:
Magnification: x100,000	
Resolution: 0.2 -10nm
Cost: Expensive 
Uses: Specimens must be dead, dried and coated with heavy metals; Black & white; Complex preparation; Can see details inside of cells; Produces 3D images

TEM:
Magnification: x500,000	
Resolution: 0.02 -10nm
Cost: Expensive 
Uses: Specimens must be dead, dried and coated with heavy metals; Black & white; Complex preparation; Can see details of the surface of structures

CSLM:
Magnification: x2000 (can be up to x15000)
Resolution: 200nm
Cost: Expensive
Uses: Different layers at different depths; Living or dead; Distribution of molecules in cells; Laser causes chemical stain to fluoresce

Question 10

What is the magnification formula?

Answer 10

magnification = Image size / actual size

remember acronym MIA

Question 11

Define Resolution

Answer 11

resolution is the ability to distinguish between two separate points.

Question 12

Define magnification

Answer 12

magnification is how much bigger the image is than the sample of the specimen

Question 13

Converting units:

Answer 13

μm to mm:
divide by 1,000

μm to cm:
Divide by 10,000

1μm = 1,000 mm 
1cm = 10mm
1μm = 10,000 cm 
1μm = 1000 nm

Question 14

Function and structure of Nucleus

Answer 14

contains coded genetic information in the form of DNA molecules (DNA directs synthesis of all proteins required by the cell).
DNA contained within a double membrane called a nuclear envelope which contains nuclear pores.
DNA is too large to leave the nucleus to the site of protein synthesis in the cell cytoplasm therefore it is transcribed into smaller RNA molecules.

Question 15

Why does a nucleus have a nuclear envelope?

Answer 15

to protect it from damage in the cytoplasm

Question 16

Why does a nucleus have nuclear pores?

Answer 16

to allow molecules to move into and out of the nucleus

Question 17

How do chromosomes form? (BASIC)

Answer 17

DNA associates with proteins called histones to form a complex called chromatin. Chromatin coils and condenses to form chromosomes.

Question 18

Function of Nucleolus

Answer 18

Area within the nucleus, composed of proteins and RNA.

Responsible for producing ribosomes.

Question 19

Function of Mitochondria

Answer 19

Site of the final stages of cellular respiration.

Mitochondria helps to produces ATP molecule from aerobic respiration.

Question 20

Structure of Mitochondria

Answer 20

• double membrane

- inner membrane is highly folded to form structures called cristae and the fluid interior is called matrix.

Question 21

Function and structure of vesicles

Answer 21

Vesicles are used to transport materials inside the cell. ( transport or sensory vesicles).
Membranous sacs that have storage and transport roles AND consists of a single membrane with fluid inside.

Question 22

Function of Lysosomes

Answer 22

Lysosomes are specialised forms of vesicles that contain hydrolytic enzymes.
Responsible for breaking down waste material in cells and play an important role in the immune system as they are responsible for breaking down pathogens ingested by phagocytic cells.
Play an important role in programmed cell death or apoptosis.

Question 23

Function of Cytoskeleton

Answer 23

Present throughout the cytoplasm of all eukaryotic cells.
Network of fibres necessary for the shape and stability of a cells.
It also controls cell movement and movement of organelles within cells.
Cytoskeleton has 3 components:
- microfilaments
- microtubules
- intermediate fibres

Question 24

State the 3 components of the cytoskeleton

Answer 24

• microfilaments
• microtubules
• intermediate fibres

Question 25

Function and structure of microfilaments

Answer 25

contractile fibres formed from the protein actin.
responsible for maintenance of cell shape (tension-bearing), changes in cell shape, muscle contraction, cell motility and cell division.

Question 26

Function and structure of microtubules

Answer 26

globular tubulin proteins polymerise to form tubes(forms a scaffold-like structure) that determines shape of cell.
responsible for maintenance of cell shape (compression-resisting), cell motility, chromosome movements in cell division, organelle movements.

Question 27

Function and structure of intermediate fibres

Answer 27

gives mechanical strength to cells and helps maintain their integrity

Question 28

Function of centrioles

Answer 28

Component of the cytoskeleton present in most eukaryotic cells, except flowering plants and most fungi.
Composed of microtubules.
Two associated centrioles = centrosome

Involved in the assembly and organisation of the spindle fibres during cell division

Question 29

Function and structure of Flagella

Answer 29

Used primarily to enable cell motility
In some cells, they are used as a sensory organelle detecting chemical changes in the cellls enviroment.
Flagella is longer than cilia, and more whip-like extensions that protrude for some cell types.

Question 30

Functions and structure of cilia

Answer 30

Stationary Cilia:
present on surface of many cells.
play an important role in sensory organs e.g. nose

Mobile Cilia:
beat in a rhythmic manner, creating a current, and cause fluids or objects adjacent to the cell to move
e.g. present in trachea to move mucus away from the lungs
each cilium contains two central microtubules surrounded by 9 pairs of microtubules arranged like a wheel, known as the 9+2 arrangement (pairs of microtubules slide over each other causing the cilia to move in a beating motion)

Question 31

State the two types of endoplasmic reticulum

Answer 31

• Smooth endoplasmic reticulum (SER)

- Rough endoplasmic reticulum (RER)

Question 32

Structure of Endoplasmic reticulum (ER)

Answer 32

network of membranes enclosing flattened sacs called cisternae.
connected to the outer membrane of the nucleus

Question 33

Function of Smooth endoplasmic reticulum (SER)

Answer 33

responsible for lipid and carbohydrate synthesis and storage
Transport / synthesis / metabolism of fats / lipids / steroids (hormones) / carbohydrates.

Question 34

Function of Rough endoplasmic reticulum (RER)

Answer 34

has ribosomes bound to the surface

responsible for the synthesis and transport of proteins

Question 35

Function and structure of ribosomes

Answer 35

ribosomes are the site of protein synthesis!!!
can be free-floating in the cytoplasm, or attached to endoplasmic reticulum forming RER.
Not surrounded by a membrane, and they are constructed of RNA molecules made in the nucleolus of the cell.

Question 36

Function and structure of Golgi apparatus

Answer 36

compacted structure of cisternae and does not contain ribosomes.
it has a role in modifying proteins and ‘packaging’ them into vesicles.

Question 37

Describe how a cell makes and secrets a protein

Answer 37

1. The nucleus is the site of ribosome and mRNA manufacture
2. Protein synthesis occurs on the ribosomes bound to the Rough endoplasmic reticulum (RER)
3. Proteins are transported from RER to Golgi body by transport vesicles.
4. Golgi body further processes the proteins (by adding sugar chains etc.)
5. Vesicles containing proteins are ‘pinched off’ the go lei body, packaged into secretory vesicles and move towards the plasma membrane.
6. Vesicles fuse with the plasma membrane and undergo exocytosis.

Question 38

Define Prokaryotic

Answer 38

single-celled organelles within a simple structure (uni-cellular) of just a single undivided internal area called the cytoplasm.

Question 39

Define Eukaryotic

Answer 39

make up multicellular organisms

more complicated internal structure as it contains a membrane-bound nucleus and cytoplasm