Structures in Cells

Question 1

Plasma membrane

Answer 1

Made of phospholipids. Prevents movement of large hydrophilic molecules into cell.

Question 2

Membrane Protein functions

Answer 2

Integral: Enzymes, receptors, linkers (attach to extracellular fibres to provide integrity), tight junctions.
Transmembrane: Channel proteins.
Superficial: Glycoproteins. Used for self-identification.

Question 3

Nucleus

Answer 3

Double phospholipid membrane bound with nuclear pores.
Intermediate filaments form nuclear lamina and nuclear matrix for structural integrity.
Contains DNA wound 2 times around a cluster of 8 histones to form a nucleosome.
Nucleolus present to produce ribosomal RNA and ribosomes.

Question 4

Ribosomes

Answer 4

Made of two subunits consisting of rRNA. Can be free or bound to endomembrane.
Free: Produces proteins used in cell.
Bound: Produces extracellular proteins or lysosomal proteins.

Question 5

Rough endoplasmic reticulum

Answer 5

Part of endomembrane. Synthesises, labels and packages proteins into vesicles to be transported to Golgi apparatus. Proteins are folded here by chaperone proteins
Produce some phospholipids for membranes. Integral membranes embedded into membranes here.

Question 6

Smooth endoplasmic reticulum

Answer 6

Produces lipids, such as hormones, steroids and phospholipids of membranes. Involved in carbohydrate metabolism and detoxifies toxins by sticking a hydroxyl on the molecule to increase solubility.

Question 7

Golgi Apparatus

Answer 7

3-20 stacks of membranous sacs with a shipping trans face and a receiving cis face.
Proteins are modified and tagged to sort them into correct secretory vesicles. This occurs in the medial cisternae.
Modifications can include phosphorylation (activation), addition of sugar chains (interactivity), ubiquitination (direction).
Polymer synthesis, secreted from cis-face.

Question 8

Lysosome

Answer 8

Membrane bound vesicle of hydrolytic enzymes in acidic conditions. Used to digest organelles (autophagy- organelle is placed into vesicle and fused with lysosome) and entire cells (autolysis).

Question 9

Mitochondria

Answer 9

Double membrane bound organelle involved in synthesis of ATP. Has own DNA and ribosomes to produce proteins required for aerobic respiration.

Question 10

Cytoskeleton

Answer 10

Form a dome like scaffold to allow for even distribution of pressure. Organelles are anchored these frameworks.
Can be used for transport within the cell.

Question 11

Microfilaments

Answer 11

Thin helical rod made of actin -7nm diameter.
Cortical filaments form a network under the plasma membrane to provide support. Said network binds to proteins on the membrane as anchorage,
Forms pseudopoda for movement.

Question 12

Intermediate filaments

Answer 12

Cytoplasmic. 8-12 nm diameter. Bears tension in heavy stress areas and provides structure for cellular projections. Provides scaffolding for organelles. Very permanent.

Question 13

Microtubules

Answer 13

25nm diameter formed from alpha and beta tubulins forming a coiled dimer. One end grows and shrinks faster that the other.
Provides structural integrity
Involved in transport within cells like movement of chromatids in mitosis, or the movement of vesicles by motor proteins along it.
Grows from a centrosome near the nucleus outwards towards the periphery.
Forms centrioles, which is a set of 9 microtubule triplets.
Flagella and cilia also made of microtubules in a 9+2 arrangement. Motion is controlled by dyenins.

Question 14

Peroxisomes

Answer 14

Vesicles of peroxidase and catalase. Breaks down and detoxifies toxic products of metabolism. Found in liver.

Question 15

Proteasomes.

Answer 15

4 barrel shaped structures joined to a core. Degrades cytosolic proteins by protease action.