biological molecules and cellular organelles

Question 1

state the key constituents of membranes, then identify them on a diagram.

Answer 1

• Phospholipid
• Polar hydrophilic head
• fatty acid hydrophobic tails
• Glycolipid
• Glycoprotein
• Carbohydrate chain
• Cholesterol
• Peripheral/intrinsic protein
• Transmembrane pore
• Phospholipid bilayer

Question 2

Name the four levels of protein structure

Answer 2

Primary
Secondary
Tertiary
Quaternary

Question 3

What are the types of secondary protein structures

Answer 3

Beta pleated sheets

Alpha helix

Question 4

What process is associated with each level of structure?

Answer 4

primary - assembly
secondary - folding
tertiary - packing
quaternary - interaction

Question 5

How does phospholipid structure enable membrane formation ?

Answer 5

• Phosphate head is hydrophilic and tail is hydrophobic.

- In water they automatically arrange themselves and form a membrane because of these properties ( amphipathic)

Question 6

State the compartments in animal cells

Answer 6

nucleus 
mitochondria 
endoplasmic reticulum 
Golgi 
lysosome
endosome 
cytosol 
peroxisome

Question 7

state the function of the nucleus

Answer 7

Houses and controls the genome – replication and transcription Production of ribosomes

Question 8

state the function of the mitochondria

Answer 8

Produces the energy (cellular ATP by oxidative phosphorylation) required for cellular life and functions, cellular metabolism both catabolic and anabolic, calcium ion homeostasis, programmed cell death and apoptosis

Question 9

state the function of endoplasmic reticulum

Answer 9

Capture and processing of proteins destined for membranes or secretion (includes to lysosomes), formation of phospholipids

Question 10

state the function of the Golgi

Answer 10

Located near the ER and is part of the cell’s manufacturing and supply chain (goods in - cis network; main processing area; goods outwards - trans network). Vesicles from the RER are ‘checked over’ and sent back to RER if wrongly delivered. Correctly delivered proteins and lipids pass into the cisternae of the Golgi stack where they are prepared for either export outside the cell or for transport to other parts of the cell.

Question 11

state the function of

Lysosome/endosome

Answer 11

Processing materials taken into the cells, recycling of old organelles

Question 12

state the function of cytosol

Answer 12

Bounded by plasma membrane and outer membranes of all organelles – houses all other components, metabolism, protein synthesis, cytoskeleton, lipid & glycogen storage etc

Question 13

state the function of peroxisome

Answer 13

Involved in lipid metabolism, conversion of reactive oxygen species (ROS) into safer molecules (for example H2O2 into water and oxygen)

Question 14

What moves in and out of the nucleus, and through what specific structures?

Answer 14

RNA – mRNA, ribosomal components, raw materials for DNA processing, proteins etc destined for the interior of the nucleus – enzymes, histones etc
Through nuclear pores

Question 15

What cytoskeletal structure that forms forms transiently during cell division and allows separation of chromosomes, to form daughter cell nuclei ?

What is its main components ?

Answer 15

Mitotic or Meiotic spindle

microtubules, made of tubulin

Question 16

Name the THREE components of the cytoskeleton

Answer 16

Actin microfilaments
microtubule
intermediate filaments.

Question 17

What is the function of actin microfilaments

Answer 17

provide protrusive and contractile forces

Question 18

what is the function of microtubules

Answer 18

form a polarised network allowing organelle and protein movement throughout the cell

Question 19

what is the function of intermediate filament ?

Answer 19

e most rigid component, responsible for the maintenance of the overall cell shape.

Question 20

What are the TWO types of Endoplasmic Reticulum and what are their respective functions

Answer 20

SMOOTH ER – small, interconnected tubules. It functions in the biosynthesis of lipids, phospholipids, and cholesterol for steroid (in the liver, SER contains large amounts of cytochrome P450 for detox of drugs and alcohol; in muscle the SER is termed the sarcoplasmic reticulum and stores and releases Ca2+ ion for muscle contraction).

ROUGH ER - broad flat cisternae studded with ribosomes and has a major role in protein synthesis. The two types interconnect and both are connected to the nuclear envelope

Question 21

role of signal peptides/sequences in telling certain proteins that they must go to the RER

Answer 21

Proteins destined for the RER have a sequence in their gene sequence that is translated by a ribosome to form a “signal peptide”.

The signal peptide binds to the endoplasmic reticulum, and once there the rest of the protein is translated and fed though the membrane of the RER into its interior.

There are distinct signal sequences to direct proteins to various parts of the cell –

eg the nuclear localisation signal for sending proteins into the nucleus, similar mechanisms to ensure that vesicles budded from the Golgi go to the correct part of the cell also.

Question 22

Outline relationship between

endosomes, lysosomes and Golgi and their functions

Answer 22

Endosomes receive materials taken into the cell through endocytosis into vesicles. The endosomes sort and recycle membrane components to the cell surface and send the rest on to the lysosomal system, where they are joined by Golgi vesicles containing enzymes that break down the vesicle contents into fundamental component that can be reused by the cell.

Phagocytosis is similar but a number of things can occur after/during. The cell could present some part of the material on its cell surface- antigen presentation. And/or the immune cell could then undergo apoptosis (organised cell death)

Question 23

. What distinguishes different cell types?

Answer 23

Variations and specialisations of structure in different cell types associated with different functions

Question 24

How are such differences generated?

Answer 24

Differential gene expression: against a background of housekeeping genes other specific set of luxury genes are expressed that code for the proteins that typify that differentiated cell (transcription factors triggered by external signals control this differentiation)

Question 25

name and describe the key modifications in the following cell types:

Answer 25

Skeletal muscle cell: cytoskeleton, SER, plasma membrane

Nerve cell body: Golgi and RER

Small intestine epithelial cell: apical part of the plasma membrane many fold – microvilli, with cytoskeletal support