Cell Organelles - Structure-Function Relationship

Question 1

What is a Cell Membrane?

Answer 1

"Plasma membrane is a complex of:
 → Lipids (amphipathic: Amphipathic: having hydrophilic and hydrophobic properties)
 → Proteins
 → Glycoproteins
 → Peptidoglycans
 → Glycosaminoglycans

○ All cells are surrounded by as plasma membrane

→ Single membrane = lipid bilayer

○ The membrane is selectively permeable –> intracellular fluid is different from extracellular fluid
“

Question 2

What makes cell membranes selectively permeable?

Answer 2

”
It is the amphipathic nature of the lipid bilayer that gives the membrane is the selective permeability property.

○ Hydrophobic tails

○ Hydrophilic heads

○ Channels and pores are needed to transport hydrophilic solutes across membrane”

Question 3

What is a cell wall?

Answer 3

”
○ Plant cells and some bacteria have a cell wall surrounding the cell membrane ○Further limits the passage of molecules in and out the cells
“

Question 4

What is the difference between Plant cell Walls and Bacterial Cell Walls?

Answer 4

”
○ Plant cell walls composed of cellulose
→ Complex carbohydrate
→ Digested by cellulase which animals don’t possess
○ Bacterial cell walls composed of peptidoglycans
→ Can also be surrounded by gelatinous polysaccharide layer referred to as capsule, glycocalyx or slime layer
→ Can stain bacteria with Gram stain: useful to distinguish between bacteria for diagnostic purposes
-Gram Positive Bacteria: single layer in the cell wall. Stains violet
-Gram Negative bacteria: Several layer to cell wall. Stains red
-Difference due to structure, +ve: uniformly thick peptidoglycan layer, -ve very thin pepitioglycan with outer membrane”

Question 5

Name the cell surface appendages and their functions:

Answer 5

”
→ To move the cell: flagella/cillia
→ To move ECF: cillia
→ To increase the cell’s surface area: villi/microvilli”

Question 6

What is the nucleus?

Answer 6

”
○ Double Membrane-bound (nuclear envelope) organelle considered the control center of the cell
○ Contains the cells blueprint for proteins: DNA. Usually in the form of chromosomes
→ Chromosomes = condensed chromatin
→ Chromatin = DNA + Histone proteins
→ Contained in nucleolus (RNA/electron dense region) - site with the nucleus where transcription and ribosome synthesis occurs. Note nucleolus does not have membrane”

Question 7

What is the function of the Nucleus?

Answer 7

”
○ In the first stage of mitosis, need to replicate DNA blueprint
○ In non-dividing cells, use DNA blueprint for protein synthesize
1. Transcription of DNA to RNA in nucleus
2. Translation of RNA to proteins in ERRNA = messenger RNA (mRNA), ribosomal RNA, transfer RNA (tRNA) transcribed from DNA”

Question 8

What are centrioles?

Answer 8

”
○ Only found adjacent to nucleus in animal cells
○ Perpendicular pair of specialist microtubules (tubulin)
○ Organizes mitotic (or meiotic) spindle - spindle used to separate sister chromatids”

Question 9

What is the mitochondria?

Answer 9

“• The powerhouse of the cell• Bound by a double membrane• Inner membrane and outer membrane separated by aqueous inner membrane space• Inner mitochondrial membrane (IMM)
○ Convoluted into cristae = increased SA for respiration reactions such as electron transport chain.• Mitochrondrial matrix: fluid that surrounds the cristae
○ Contains enzymes for respiration• Contains mitochondrial DNA (maternally inherited) which codes for the enzymes used in respiration: does not make all cell proteins.”

Question 10

What is the function of the mitochondria?

Answer 10

“• Mitochondria contains a series of oxidative enzymes that catalyze aerobic catabolism of fuels such as carbohydrates, fatty acids and amino acids/proteins)• Harnesses energy of fuels as ATP by oxidative phosphorylation
○ The process generates and metabolise reactive oxygen species and free radicals• Overall Oxidative respiration of glucose:
○ C6H12O6 + 6O2 = 6CO2 + 6H2O + ATP• Sites of respiration:

• Mitochondria also mediate cell death, apoptosis”

Question 11

What are chloroplasts and what is their function?

Answer 11

• Bounded by double membrane• Has its own DNA• Site of photosynthesis!Present in plant cells only

Question 12

What is the function of ribosomes?

Answer 12

• mRNA formed from nucleus (nucleolus) is translated into an amino sequence (peptide/protein) by ribosomes

Question 13

What are ribosomes?

Answer 13

”
· Ribosomes have two subunits: small and large
○ Each subunit is a complex of rRNA and proteins
→ The enzymatic component is rRNA
· eukaryotes and prokaryotes have different types of ribosomes

· This difference can be exploited as you can target bacterial cells with antibiotics that don’t affect”

Question 14

What are polysomes

Answer 14

”
· Polysomes are several ribsomes that translate the same mRNA template. Like a chain
→ Not common as most ribsomes are associates on the ER”

Question 15

What is the Endoplasmic reticulum?

Answer 15

Continuous, highly convoluted membrane system that spans from the nucleus to the plasma membrane. Goes from rough to smooth ER

Question 16

What is the difference between Rough and Smooth Endoplasmic Reticulum?

Answer 16

Rough ER has ribsomes attached to its membrane.

Question 17

What is the function of Rough ER?

Answer 17

”
○ Rough ER - site of protein synthesis (translation)- Proteins are also glycosylated i.e. have sugars on put them. This provides protection”

Question 18

What is the function of Smooth ER?

Answer 18

Smooth ER- site of lipid synthesis and involved in metabolism of fats and steriod hormones

Question 19

Where the synthesis occur on ER?

Answer 19

Synthesis generally occurs in lumen of the cisternae (finger-like projections)

Question 20

What is the Golgi apparatus?

Answer 20

“• Series of specialized, stacked cisternae through which proteins and lipids are processed and ‘labelled’ prior to:
○ Insertion into the plasma membrane
○ Secretion• Golgi apparatus then ‘sorts’ molecules to its final destination”

Question 21

How does the Golgi modify lipids and proteins?

Answer 21

“• Enzymes in the Golgi can add carbohydrates to form
○ Glycolipids
○ Glycoproteins”

Question 22

How do molecules travel to the Golgi?

Answer 22

• Molecules enter on the cis face (adjacent to ER) and exit from the trans face - move via vesicular trafficking

Question 23

What are vesicles?

Answer 23

”

○ Small, spherical sealed, single membrane (lipid bilayer), contains intracellular fluid

Question 24

What is vesicular trafficking?

Answer 24

”
• The process by which proteins and other macromolecules move across the cell via vesicles

○ Vesicle buds off from one membrane (cisterna)

○ Vesicles passes through the cytoplasm and fuses with another membrane

○ Traffics lumenal and membrane contents of vesicle (more common for contents to be within lumen rather than its membrane)
“

Question 25

Where does glycosylation of proteins occur?

Answer 25

”

• Glycosylation of proteins occurs in both ER and golgi”

Question 26

What role does the ER have in regards to proteins other than synthesis?

Answer 26

”

• Glycosylation of proteins occurs in both ER and golgi”

Question 27

Name the 3 digestive organelles

Answer 27

• Endosomes- Lysosomes- Peroxisomes

Question 28

What are endosomes?

Answer 28

”
→ Incoming vesicles formed by endocytosis i.e. when a cell takes up matter by the invagination of its membrane to form a vacuole
→ Buds from plasma membrane
- Pinocytosis (endocytosis of fluids - cell drinking)
- Phagocytosis (the endocytosis of molecules -cell eating) “

Question 29

What are the three types of endosomes?

Answer 29

”
→ Three types of endosomes: early, recycling and late endosome (EE, RE, LE)
→ EE: the initial vesicle that has budded of the membrane and moved into cells
→ RE: once entered, vesicle may return back to the plasma membrane. Vesicle may have receptor proteins that the cell wants to reuse and so the RE reinserts these receptors by exocytosis
→ LE: if contents are going to be used further, they are modified to form LE. LE may go to the Golgi and fuse. More often however, the LE enter the lysosomal pathway whereby the contents undergo degradation”

Question 30

What are lysosomes?

Answer 30

”
→ Late endosomes fuses with vesicles containing ‘lysozymes’ (acid hydrolases) to form lysosomes
→At low pH, the lysosomes hydrolyse chemical bonds to degrade contents of lysosomes”

Question 31

What are functions of Peroxisomes?

Answer 31

→Detoxifies harmful substances with the enzymes they possess, involved in detoxification→ Also involved in the initial catabolism of long chained fatty acids, branched chain fatty acids and polyaminesExample: mitochondria produce a lot of harmful free radicals during respiration and so peroxisomes help neutralize these compoundslarge number presesnt in the cells of liver and kidneys as these organs detoxify harmful substances including those found in drugs*Malfunctioning peroxisomes are associated with diseases may result in the accumulation of FAs, particularly seen in the nervous system

Question 32

Name 2 of the enzymes found in Peroxisomes?

Answer 32

"
 → Contains peroxidase enzymes: breaks down hydrogen peroxides into water
 - RH2 +O2 →R+H2O2 (HOOH)
 → Also contains catalase enzymes
 - RH2 +H2O2 →2 x H2O"

Question 33

Prokaryotes vs Eukaryotes

Answer 33

-Eukaryotes possess membrane bound organelles whilst prokaryotes do not, i.e. no nucleus, mitochondria, Golgi apparatus-only common organelle = ribosomes
• ‘‘karyon’’ = ‘nut / kernal’’ (refers to nucleus surrounded by double membrane/ nuclear envelope)
Prokaryotes do not have a nucleus ‘before the nucleus)

Question 34

Where is genetic information stored in bacteria?

Answer 34

The nucleiod=circlular molecule of DNA, possesses no histones so therefore is considered ‘‘naked’’

Question 35

Where does metabolism occur in Prokarya?

Answer 35

Metabolism occurs in the cytosol as they do not possess mitochondria or ER

Question 36

What are the two Kingdoms of Prokarya

Answer 36

”
○ Prokarya
→ Distinguished by testing whether gram staining: gram positive (violet) vs gram negative (red)
→ 12 phyla (e.g. cyanobacteria, spirochetes and chlamydiae)
○ Archaea
→ Euryachaeota vs Crenarchaeota
→ 6 phyla (e.g. halophiles, methanobacteria and thermococci)”

Question 37

Name the 4 prokaryote morphologies?

Answer 37

"
 ○ Cocci (spherical)
 ○ Bacillus (rod/rod-like)
 ○ Spirochetes (spiral)
 ○Vibrio (curved, ''commas'")

Question 38

True or false: Prokaryotes are always unicellular

Answer 38

“False. Depends on life stage.

○ Archaea always unicellular

○ Bacteria usually unicellular (e.g. e.coli, pseudomanas, streptococcus)

○ Some bacteria have a multicellular stage in their life cycles (e.g. myxobacteria) or form colonies (cynaobacteria)
“

Question 39

What are kingdoms of Eukaryotes?

Answer 39

"
 ○ multicellular
 → Animals
 → Plants
 → Fungi
 ○ Unicellular
 → Yeast
 → Fungi"

Question 40

Why do eukaryotic cells differ so widely?

Answer 40

They differ due to function

Question 41

Give examples of cells differing in nuclei

Answer 41

“all mammals - mature erythrocytes lack nuclei - maximise O2carrying capabilities
→ Most non-mammalian vertebrates have nucleated RBC with some exceptions such as salamanders
→ ‘lens fibre’ cells in the eye have no nucleus as it would impair light being passed through eyes. (also have not mitochondria or ER)”

Question 42

Give examples of cells differing in mitochondria:

Answer 42

”
→ Hepatocytes have c. 2,000 mitochondria per cell which accounts for about 20% of cell volume —> due to high metabolism as result of its function of producing proteins, high bile salts etc
→ Unicellular organisms usually have a single mitochondrion
→ Erythrocytes and some unicellular eukaryotes have zero mitochrondrion: maximises oxygen carrying potential”

Question 43

Name a cell with a different type of mitochondria:

Answer 43

Sperm contain large number of spiral mitochondria wrapped around the flagellum (midpiece). Generates ATP to fuel its high motility.Number of mitochondria linked to fertility of sperm. The more mitochondria, the greater chance of fertilising the egg.

Question 44

What type of cell will have plentiful Golgi?

Answer 44

Cells involved in biosynthesis have a high number of Golgi

Question 45

What are Micelles?

Answer 45

Micelles = lipid molecules that arrange themselves in a spherical form in aqueous solutions. Single layer arrangement as opposed to double layer of lipids as seen vesicles”