Cells: Cell Structure

Question 1

Cell organisation

Answer 1

Prokaryotes & Eukaryotes

Question 2

Differences between Prokaryotes & Eukaryotes (7)

Answer 2

Size: prokaryotes = smaller, eukaryotes = larger
DNA: prokaryotes = circular, eukaryotes = linear
Nucleus: only in eukaryotes
Internal organisation: prokaryotes = little, eukaryotes = high
Membrane-bound organelles: only eukaryotes
Chromosomes: prokaryotes = single, eukaryotes = 2+
Cell wall: prokaryotes = peptidoglycan, eukaryotes = cellulose if present
Examples: prokaryotes = bacteria, eukaryotes = animals, plants

Question 3

Cell Organelles

Answer 3

nucleus = control centre
mitochondria = power house
chloroplasts = kitchen
endoplasmic reticulum = transport network
lysosomes = garbage/recycling bin
Golgi body = post office
vacuole = storage
ribosomes = 
(cell membrane = customs)

Question 4

Nucleus

Answer 4

Structure

• average diameter 5um
• nuclear envelope = double membrane
• nuclear pores = allow substance exchange
• nucleolus = spherical body, no membrane, composed of DNA & proteins, site for ribosomal RNA synthesis
• chromatin = no specific shape, made of DNA & protein, condense to form chromosomes during cell division

Function

• store and transmit genetic information
• control centre of the cell

Question 5

Mitochondria

Answer 5

often found in higher quantities in muscle cells etc.

Structure

• 10um in length
• double membrane = outer resembles cell, inner resembles prokaryote & has numerous folds/cristae
• contains mitochondrial DNA (possible origin as aerobic bacteria)

Function

• powerhouse of the cell
• produce energy through aerobic respiration in the form of ATP (latter stages)

Question 6

Chloroplasts

Answer 6

type of plastid found in plant cells & algae

Structure

• double membrane
• thylakoids = system of membranous flattened sacs inside the internal membrane, arranged in stacks called grana which are joined by lamellae, contain photosynthetic pigment chlorophyll
• stroma (fluid) surrounds thylakoids & enzymes

Function

• carry out photosynthesis (light energy - chemical energy)
• “kitchen” of the cell

Question 7

Endoplasmic Reticulum

Answer 7

“transport network” extending through the cytoplasm from the nuclear membrane to the cell membrane

Structure

• a system of membranes spread in the cytoplasm
• rough E.R. = ribosomes attached
• smooth E.R. = no ribosomes attached

Function

• rough E.R. = site of protein and membrane synthesis eg. glycoproteins for cell membrane receptors
• smooth E.R. = lipid synthesis, metabolism of carbohydrates, transports proteins in vesicles from E.R. to Golgi bodies

Question 8

Golgi body

Answer 8

also Golgi apparatus, Golgi complex
often higher quantities in secretory cells eg. gland cells producing saliva, hormones etc.

Structure
- stacks of flattened sacs made of smooth membrane

Function

• involved in packaging & secretion of proteins & carbohydrates
• receives packages from rough E.R.
• modifies & packages into vesicles for transport out of the cell (exocytosis)

Question 9

Lysosomes

Answer 9

recycling component

Structure
- membrane vesicles (found mostly in animal cells)

Function
- contain hydrolytic enzymes to digest macromolecules eg. food particles, foreign molecules or break down “worn out” cell organelles

Question 10

Vacuole

Answer 10

plants - large vacuoles, animals - small vacuoles

Structure
- large membrane-bound fluid-filled vesicle

Function

• maintain salt & water balance
• contribute to cell growth & shape by the intake of water
• store waste products, food, sometimes pigments

Question 11

Ribosomes

Answer 11

Structure

• small, made of rRNA (produced by nucleoli)
• usually attached to E.R.

Function
- involved in translation, site/platform for protein synthesis

Question 12

Cytoskeleton

Answer 12

Function

1. give cells their shape
2. strengthen cell
3. involved in cell movement
4. holds cell organelles in place

Structure

• Microtubules: tube-like structure, larger in diameter, made of protein “tubulin”; function: part of cilia/flagella, help in movement of cell or fluid around it; *spindle fibres made of microtubules
• Microfilaments: ‘twisted pearl necklace’, smaller in diameter, made of protein “actin”; function: movement of cell organelles eg. chloroplasts, pinching of membrane to form daughter cell, formation of vesicles
• Intermediate Filaments: medium size, made of proteins; function: strengthen cells & tissues eg. skin cells (wear & tear)

Question 13

Cell Membrane

Answer 13

plasma membrane, “Fluid-Mosaic” model
Singer & Nicholson 1972

Structure

• phospholipid bilayer with embedded proteins
• “fluid” as lipids & proteins move laterally, not static
• selectively semi-permeable

Function

1. controls movement of substances into/out of cell
2. separates internal cell components from external environment
3. enables attachment of cytoskeleton
4. enables cell recognition