B2.2 Organelles and compartmentalisation

Question 1

what are organelles

Answer 1

separate subunits of cells

Question 2

what are the only organelles common to eukaryotes and prokaryotes

Answer 2

cell membranes and ribosomes

Question 3

what is the advantage of separating the nucleus and the cytoplasm

Answer 3

keeps DNA separate, protecting it from many cellular reactions that occur in the cytoplasm
allows gene transcription and translation to be kept separate

Question 4

what are exons

Answer 4

the sections of the gene that carries important data ( coding for amino acids)

Question 5

what are introns

Answer 5

the non coding sequences in the gene

Question 6

what is post transcriptional modification

Answer 6

since introns are useless, the introns are removed as soon the mRNA has been formed through an enzyme catalysed reaction
also known as RNA splicing

Question 7

what is the result of RNA splicing

Answer 7

the shortened lengths of mRNA are described as mature and can be passed on for protein synthesis

Question 8

what is the advantage of RNA splicing

Answer 8

for eukaryotic cells, variants of protein can be produced from a single gene

Question 9

why is RNA splicing not possible in prokaryotes

Answer 9

there is no nuclear membrane, meaning mRNA instantly meets ribosomes
So prokaryote genes do not have introns

Question 10

what is the nuclear membrane made of

Answer 10

a phospholipid bilayer, permeable only to small, non polar molecules

Question 11

what is the role of the nuclear pores

Answer 11

the nuclear pores in the nuclear envelope control the exit of mRNA and movement of proteins

Question 12

what are the nuclear pores made of

Answer 12

specific proteins forming a specific structure that is quite tiny ( 100 nm)

Question 13

what is the estimate of nuclear pores present in the nuclear membrane

Answer 13

quite numerous, around 1/3rd of the nuclear membrane

Question 14

what does the presence of nuclear pores suggest to us

Answer 14

suggests that communication between nucleus and cytoplasm is quite important

Question 15

the selective movement of proteins and RNA through the nuclear pores plays ___?

Answer 15

an essential role in regulating eukaryotic gene expression

Question 16

how does nuclear pores differ in transport mechanisms of other organelles

Answer 16

they are able to transport proteins in their folded conformation and ribosomal components in assembled particles

Question 17

does export of RNA through nuclear pores require energy

Answer 17

yes, its an active process

Question 18

where is Ribosomal RNA assembled

Answer 18

assembled with ribosomal proteins in the nucleolus and ribosomal subunits are then transported into the cytoplasm

Question 19

what does compartmentalization in cells allow

Answer 19

allow for the correct concentration of metabolites to be present for specific metabolic process and the appropriate enzymes to be present
incompatible biochemical processes can be separated

Question 20

why is compartmentalisation useful in lysosomes

Answer 20

they contain digestive enzymes in an acidic environment
the pH of the cell is slightly alkaline in case of leakages
it allows functions to occur that would not be possible in the rest of the cell

Question 21

explain compartmentalization in phagocytic vacuoles

Answer 21

the formation of phagolysosome ( phagocytic vacuole and lysosome) is required and creates a contained space where digestion can take place at a low pH.

Question 22

explain the process of respiration in the cell

Answer 22

in the cytoplasm, through a process called glycolysis, which is anaerobic produces pyruvate, which then diffused into the mitochondria, where aerobic respiration takes place

Question 23

what happens when pyruvate goes inside the mitochondria

Answer 23

carbon is removed along with hydrogen which is split into protons and electrons
electrons pass down a sequence of proteins in the inner membrane, releasing energy that pumps into protons, which create an electrochemical gradient
this passes through ATP synthase, generating ATP

Question 24

how do cristae help in the generation of ATP

Answer 24

assists by increasing the surface area of ATP synthase, leading to more ATP production

Question 25

what is the process of producing ATP in the mitochondria called

Answer 25

the Krebs cycle, which occurs in the matrix of the mitochondria

Question 26

what is the structure of the membranes in the chloroplasts

Answer 26

double membrane, along with a third inner membrane that folds extensively at various points known as thylakoids

Question 27

what is the structure of the thylakoids

Answer 27

organized into flat compact circular piles called grana/granum
between the grana, loosely arranged membranes are suspended into a watery stroma
separate grama are connected by lamella

Question 28

where are chlorophyll molecules found

Answer 28

grouped together in structures called photosystems, held in the thylakoid membrane by proteins. Large surface area of thylakoid membrane optimised the ability to harvest light energy

Question 29

what is the Calvin cycle

Answer 29

light energy causes electrons to pass down a chain, causing protons to be pumped into the thylakoids, leading to a build up of proteins
protons flow down electrochemical gradient through ATP synthase proteins, generating ATP, leading to the production of glucose

Question 30

why is compartmentalisation an advantage in chloroplasts

Answer 30

allows the separation of light harvesting activity of the chloroplasts in the thylakoids from the enzymes and the substrates of the Calvin cycle in the stroma

Question 31

what is the inner nuclear membrane lined with

Answer 31

nuclear lamina , which is a meshwork of filaments that extend into the interor of the nucleus and provide structural support
composed of lamins, a fibrous protein

Question 32

what happens to the nuclear envelope when the cell divides through mitosis and meiosis

Answer 32

nuclear envelope dissociates into small vesicles enabling the chromosomes to encounter the cytoplasm and spindle apparatus , central to manipulating chromsomes

Question 33

what is a polysome

Answer 33

when ribosomes move along the mRNA, allowing many copies of a particular protein to be produced simultanously

Question 34

what is the structure of the golgi apparatus

Answer 34

consists of stack like collection of flattenned membranous sacs called cisternae

Question 35

which way do proteins enter the golgi apparatus

Answer 35

they enter the golgi on the side facing the RER and exit on the opposite side facing the opposite side

Question 36

how are proteins moved through the golgi apparatus

Answer 36

they are transferred from one cisterna to the next. Each cisterna contains enzymes, catalysing different types of proteins modification

Question 37

what can the enzymes in the golgi apparatus caus

Answer 37

glycosylation
sulfation
phosphorylation

Question 38

explain the process of endocytosis

Answer 38

a protein binds to a receptor on the cell surface. specialised protein then acts to cause the membrane in the region to invaginate( tuck in)

Question 39

which protein helps with the formation of vesicles

Answer 39

clathrin which polymerizes into a lattice network around the growing membrane bud to form a clathrin coated pit, eventually breaking off the membrane to form a vesicle

Question 40

what happens to the clathrin on the vesicle after the vesicle is formed

Answer 40

it breaks off and attaches back to the membrane