Topic 2 - Cells (F)

Question 1

Outline the nucleus (brief structure/function)

Answer 1

-Contains the organisms hereditary material (DNA) and controls the cell’s activities.
-It’s usually spherical

Question 2

Outline the nuclear envelope

Answer 2

-A double membrane surrounding the nucleus
-The outer membrane is continuous with the endoplasmic reticulum of the cell and often has ribosomes on its surface
-It controls the entry and exit of materials in and out of the nucleus and contains the reactions taking place within it

Question 3

Outline the nuclear pores

Answer 3

-Allow passage of large molecules such as messenger RNA, out of the nucleus.
-There are typically around 3000 pores in each nucleus

Question 4

Outline nucleoplasm

Answer 4

The granular jelly-like material that makes up the bulk of the nucleus

Question 5

Outline the nucleolus

Answer 5

A small spherical region in the nucleoplasm . It manufactures ribosomal RNA and assembles the ribosomes.

Question 6

What are the functions of the nucleus

Answer 6

-Control centre of the cell through production of mRNA and tRNA hence protein synthesis
-Has the genetic material of the cell
-Manufactures ribosomal RNA and ribosomes

Question 7

Outline the structure of mitochondria

Answer 7

-Rod shaped and 1-10um in length
-Made up of cristae and the matrix
-Around the organelle is a double membrane that controls the entry and exit of material. The inner of the two membranes is folded to form extensions known as cristae

Question 8

Outline the cristae

Answer 8

Extensions of the inner membrane which extend across the whole width of the mitochondrion, giving a large surface area for the attachment of enzymes and other proteins involved in respiration.

Question 9

Outline the matrix

Answer 9

-Makes up the remainder of the mitochondria, it contains protein, lipids, ribosomes and DNA that allows the mitochondria to control the production of some their own proteins, Many enzymes involved in respiration are found in the matrix

Question 10

Outline the function of mitochondria

Answer 10

-Site of aerobic respiration
-They are responsible for the production of ATP which is the energy-carrier molecule from respiratory substrates like glucose

Question 11

What is endoplasmic reticulum

Answer 11

An elaborate three-dimensional system of sheet-like membranes, spreading through the cytoplasm of the cells. It is continuous with the outer nuclear membrane. The membranes enclose a network of tubules and flattened sacs called cisternae

Question 12

Outline rough endoplasmic reticulum

Answer 12

-Has ribosomes present on the outer surfaces of the membranes
-It provides a large surface area for protein and glycoprotein synthesis
-It provides a pathway for transporting materials through the cell (especially proteins)

Question 13

Outline smooth endoplasmic reticulum

Answer 13

-Lacks ribosomes on its surface and is often more tubular in appearance
-It synthesises, stores and transports lipids
-It synthesises, stores and transports carbohydrates

Question 14

What is the structure of Golgi apparatus

Answer 14

It consists of a stack of membranes that make up flattened sacs, or cisternae, with small rounded hollow structures called vesicles

Question 15

How does the golgi apparatus work?

Answer 15

-Proteins and lipids produced by endoplasmic reticulum pass through in a strict sequence
-The golgi modifies them often adding non-protein components to them.
-It labels them so they can be sorted and sent to the correct designation
-Once sorted the modified proteins and lipids are transported in vesicles which may move to cell surface, where they fuse with the membrane and release their contents to the outside

Question 16

Golgi apparatus functions

Answer 16

-Add carbohydrates to proteins to form glycoprotein
-Produce secretory enzymes (e.g. those secreted by the pancreas)
-Secrete carbohydrates such as those used in making cell walls in plants
-transport, modify and store lipids
-Form lysosomes

Question 17

How are lysosomes formed

Answer 17

When the vesicles produced by the Golgi contain enzymes such as proteases and lipases.

Question 18

Outline lysosome structure **

Answer 18

-Contain enzymes such as proteases and lipases aswell as lysozymes
-As many as 50 enzymes may be contained in a single lysosome

Question 19

What are lysozymes

Answer 19

Enzymes that hydrolyse the cell walls of certain bacteria

Question 20

What are the functions of lysosomes

Answer 20

-Hydrolyse materials ingested by phagocytic cells (e.g. white blood cells and bacteria)
-Release enzymes to the outside of the cell (exocytosis) in order to destroy material around the cell
-Digest worn out organelles so that the useful chemicals they are made of can be re-used.
-Completely break down cells after they have died

Question 21

Outline 80S ribosomes

Answer 21

Found in eukaryotic cells, is around 25nm in diameter

Question 22

Outline 70S ribosomes

Answer 22

Found in prokaryotic cells, mitochondria and chloroplasts, is slightly smaller

Question 23

Outline ribosomes

Answer 23

-Small cytoplasmic granules found in all cells. They may occur in the cytoplasm or be associated with the RER
-They are the site of protein synthesis

Question 24

Outline chloroplasts

Answer 24

-Carry out photosynthesis
-They vary in shape and size but are typically disc shaped, 2-10um long and 1um in diameter

Question 25

Outline the chloroplast envelope

Answer 25

-A double plasma membrane that surrounds the organelle. It is highly selective in what it allows to enter and leave the chloroplast.

Question 26

Outline the grana in chloroplasts

Answer 26

-A stack of up to 100 thylakoids. Thylakoids have chlorophyll. Some have tubular extensions that join up with thylakoids in the adjacent grana
-This is where the first stage of photosynthesis occurs

Question 27

Outline the stroma in chloroplasts

Answer 27

A fluid-filled matrix where the second stage of photosynthesis takes place. Within are a number of other structures such as starchgrains enzymes and ribosomes.

Question 28

How are chloroplasts adapted for their function

Answer 28

-The granal membranes provide large surface area for attachment of chlorophyll, electron carriers and enzymes that carry out the first stage of photosynthesis
-The fluid of the stroma possesses all the enzymes needed to make sugars in the second stage of photosynthesis
-Chloroplasts contain both DNA and ribosomes so they can quickly and easily manufacture some of the proteins needed for photosynthesis

Question 29

Outline the cell wall

Answer 29

-Consists of microfibrils made up of alternating inverted cellulose molecules.
-They consist of a number of polysaccharides
-There is a thin layer called the middle lamella, which marks the boundary between adjacent cell walls and cements adjacent cells together

Question 30

Outline functions of the cellulose cell wall

Answer 30

-Provide strength to prevent the cell from bursting under pressure created by osmotic entry of water
-Give mechanical strength as a whole
-Allows water to pass long it so contributes to movement of water through the plant.

Question 31

Outline vacuoles

Answer 31

-A fluid-filled sac bounded by a single membrane may be termed a vacuole
-Within mature plant cells there is usually one large central vacuole
-The single membrane around it is called the tonoplast
-Contains a solution of mineral salts, sugars, amino acids, wastes and sometimes pigments such as anthocyanins

Question 32

What are the functions of vacuole

Answer 32

-Support herbaceous plants by making cells turgid
-The sugar and amino acids act as a temporary food store
-The pigments may colour petals to attract pollinating insects

Question 33

Outline prokaryotic cells

Answer 33

-100 times smaller than eukaryotic cells
-Single-celled organisms

Question 34

What similarity do prokaryotic and eukaryotic cells share

Answer 34

-The cell-surface membrane is mainly made of lipids and proteins. It controls the movement of substances into and out of the cell

Question 35

Outline cytoplasm/ribosomes in prokaryotic cells

Answer 35

The cytoplasm contains ribosomes but are smaller than those in eukaryotic cells (70S) v (80S)

Question 36

Outline the cell wall in prokaryotic cells

Answer 36

Supports the cell and prevents it from changing shape. It’s made from changing shape polymer called murein which is a glycoprotein

Question 37

Outline the flagellum in prokaryotic cells

Answer 37

A long hairlike structure that rotates to make the prokaryotic cell move. Not all prokaryotes have a flagellum and some have more than one.

Question 38

Outline DNA in prokaryotic cells

Answer 38

-DNA floats free in the cytoplasm. It’s circular DNA, present as one long coiled-up strand.
-Plasmids are small loops of DNA that aren’t part of the main circular DNA molecule.
-Plasmids are not always present in prokaryotic cells. Some prokaryotic have several.

Question 39

Outline capsules in prokaryotic cells

Answer 39

-Made up secreted slime.
-It helps to protect the bacteria from attack from attack by cells of the immune system

Question 40

Outline what is a virus

Answer 40

-Acellular : they’re not fact
-They are nuclei are acid surrounded by protein
-They invade and reproduce inside the cells of other organisms, these are known are known as host cells.

Question 41

Outline virus structure

Answer 41

-Unlike bacteria they have no cell-surface membrane, no cytoplasm and no ribosomes.
-They do have a protein coat, called a capsid with attachment proteins sticking out from it. The attachment proteins let the virus cling onto a suitable host cell.
-Smaller than bacteria

Question 42

What is the equation for magnification

Answer 42

Magnification = size of image / size of actual object

Question 43

Outline microscopes

Answer 43

-Instruments that produce a magnified image of an object. A simple convex glass lens can act as a magnifying glass but such lenses work more effectively if they are used in pairs in a compound light microscope
-Relatively long wavelength of light rays means that a light microscope can only distinguish between two objects if they are 0.2um or further apart.

Question 44

Outline the resolution of a microscope

Answer 44

Minimum distance apart that the two objects can be in order for them to appear as separate items.

Question 45

What does the resolution of a microscope depend on

Answer 45

-The wavelength or form of radiation used

Question 46

What is the resolution of a typical light microscope

Answer 46

-Around 0.2 um

Question 47

What is cell fractionation

Answer 47

-The process where cells are broken up and the different organelles they contain are separated out

Question 48

Why do we do cell fractionation

Answer 48

To study the structure and function of the various organelles that make up cells, it is necessary to obtain large numbers of isolated organelles

Question 49

How are tissues treated before cell fractionation

Answer 49

-Placed in a cold buffered solution of the same water potential as the tissue

Question 50

Before cell fractionation why is the tissue placed in a cold solution

Answer 50

To reduce enzyme activity that might break down the organelles

Question 51

Before cell fractionation why is the tissue placed in a solution of the same water potential

Answer 51

-To prevent organelles bursting or shrinking as a result of osmotic gain or loss of water

Question 52

Before cell fractionation why is the tissue placed in a buffered solution

Answer 52

So that the pH does not fluctuate. Any change in pH could alter the structure of the organelles or affect the functioning of enzymes.

Question 53

What is the first stage of cell fractionation

Answer 53

Homogenation

Question 54

Outline homogenation

Answer 54

-Cells are broken up by a homogeniser (blender). This releases the organelles from the cell. The resultant fluid, known as homogenate, is then filtered to remove by compete cells and large pieces of debris.

Question 55

What is the second process of cell fractionation

Answer 55

Ultracentrifugation

Question 56

Outline ultracentrifugation

Answer 56

-The process by which the fragments in the homogenate are separated in a machine called a centrifuge. This spins tubes of homogenate at very high speed in order to create a centrifugal force.
1. The tube of filtrate is placed in the centrifuge and spun at a slow speed.
2. The heaviest organelles, the nuclei, are forced to the bottom of the tube, where they form a thin sediment or pellet.
3. The fluid at the top of the tube (supernatant) is removed, leaving just the sediment of nuclei
4. The supernatant is transferred to another tube and spun in the centrifuge at a faster speed than before

Question 57

What is the process of ultracentrifugation

Answer 57

1. The tube of filtrate is placed in the centrifuge and spun at a slow speed.
2. The heaviest organelles, the nuclei, are forced to the bottom of the tube, where they form a thin sediment or pellet.
3. The fluid at the top of the tube (supernatant) is removed, leaving just the sediment of nuclei
4. The supernatant is transferred to another tube and spun in the centrifuge at a faster speed than before
5. The next heaviest organelles, the mitochondria are forced to the bottom of the tube
6. The process is continued in this way so that, at each increase in speed, the next heaviest organelle is sedimented and separated

Question 58

What do cell fractionation and ultracentrifugation allow

Answer 58

-Enabled considerable advances in biological knowledge. They allowed a detailed study of the function and structure of organelles, by showing what isolated components do.

Question 59

Outline electron microscopes