3.1: Types of Organelles and their Major Functions

Question 1

Nucleus

Answer 1

contains DNA, RNA synthesis, cell cycle

Question 2

Golgi Apparatus

Answer 2

post translational modification of proteins, protein and membrane trafficking

Question 3

Smooth Endoplasmic Reticulum

Answer 3

• Site of lipid, cholesterol, steroid biosynthesis
• Site of carbohydrate synthesis inside the lumen.
• Site of Ca+2 channels: Ca+2 level high in ER (used in cell signaling, muscle
  contraction) . Ca+2 can be released in the cytosol in response to a particular signal.

-SER is Detoxification Center for xenobiotic compounds (foreign substances, drugs)

-Hydrophobic toxins are hydroxylated by monooxygenase enzymes (P450 family
of enzymes) and then flushed out by kidney.

-Hydroxyl group is generated by activation of molecular oxygen and
electrons supplied by NADPH. The molecular oxygen is reduced to water
in the chemical process.
RH + O2 + NADPH + H+ → ROH + H2O + NADP+

-Also referred to as transitional ER. Vesicle budding site (for vesicles going to Golgi) - vesicular transport starts in the smooth ER

Question 4

Rough endoplasmic reticulum

Answer 4

A site of protein synthesis and translocation (co-translational translocation).

-Proteins in the endosomal pathway are made and translocated here.

-ER lumen is a site of post-translational protein modification, such as glycosylation,
disulfide bonds, etc.

-ER lumen is a site of surveillance for misfolded proteins

Question 5

Secretory vesicles

Answer 5

export of proteins, some plasma membrane components such as surface receptors (acetycholine)

Question 6

Endosomes

Answer 6

import of large structures such as bacteria and other cells

Question 7

mitochondria

Answer 7

oxidative respiration, cell survival, apoptosis

Question 8

choroplasts

Answer 8

photosynthesis and carbon fixation

Question 9

lysosomes

Answer 9

neutralization and digestion of endosome/phagosome contents

play important roles in neutralizing harmful
substances and recycling the contents of cells such as aging proteins.

Involved in at least 5 cellular processes

Endocytosis: digest materials brought in from the outside by endosomes
 Phagocytosis: digest bacteria and large particles
 Autophagy: donor membranes wrap organelles and fuse with lysosomes to break down
organelles and cellular components that are no longer needed.
 Autolysis: “programmed cell death” – “suicide”
 Digestion of extracellular materials: lysosomes dishcharge acid hydrolases to the
extracellular space
 Sperm head releases lysosomal enzymes to degrade oocyte surface membrane during
fertilization
 Primary lysosomes: contain acid hydrolases, but do not engage in digestive activity
 Secondary lysosomes (endolysosome): result from fusion of primary lysosome and
endosomes with particles to be digested.

Question 10

peroxisomes

Answer 10

management of oxidative rxn’s

Question 11

Clathrin coated vesicles

Answer 11

import of fluid and membrane associate proteins

Question 12

Proteins in the endosomal pathway are made and translocated here

Answer 12

RER

Question 13

Site of protein synthesis and translocation (co-translational translocation). Post translational protein modification such as glycosylation, disulfide bonds, etc.

Answer 13

RER

Question 14

Where does surveillance for misfolded proteins occur?

Answer 14

RER