Cell architecture

Question 1

What are the features of the nucleus?

Answer 1

1. Nuclear envelope: consists of outer nuclear membrane and inner nuclear membrane. The space between inner and outer membrane is called perinuclear space.
2. nuclear lamina: filament basket made of lamins, attached to inner nuclear membrane
3. Nuclear pores: nuclear import/export
4. nucleolus: dense, membrane-less structure composed of RNA and proteins. rRNA synthesis
5. chromatin: long entangled structure of DNA and proteins, during cell division, chromatins are arranged into chromosomes

Question 2

what is the general function of the nucleus?

Answer 2

• Storage of hereditary material in the form of DNA strands, referred to as chromatin.
• site for DNA replication where the whole genome is copied before the cell divides
• site for transcription in which messenger RNA (mRNA) are produced for protein synthesis.
• Production of ribosomal RNA (major component of ribosomes) in the nucleolus.
• Selective transportation of regulatory factors and energy molecules through nuclear pores

Question 3

What is the nuclear lamina?

Answer 3

• A fibrous meshwork that gives structural support to the nuclear envelope.
• Composed of proteins called lamins.

Question 4

Describe the nucleolus.

Answer 4

• within the nucleus
• Not membrane bound
• Primary site for ribosome synthesis
• Consists of highly dense macromolecules (RNA etc.)

Question 5

What is the function of the Rough ER.

Answer 5

• site for protein synthesis (ribosomes attach to ER and synthesise proteins)
• protein folding
• protein quality control
• transportation of proteins

Question 6

What are the functions of the Smooth ER.

Answer 6

• Synthesis of lipids
• Calcium ions storage
• Carbohydrate metabolism
• Synethesis of steroid hormones

Question 7

What are the main functions of the Golgi apparatus.

Answer 7

sorting, modification, packaging of proteins and lipids

Question 8

Describe the intrinsic directionality of golgi apparatus.

Answer 8

1. cis golgi network
2. cis cisterna
3. medial cisterna
4. trans cisterna
5. trans golgi network

1 is closest to the ER and 5 is the furthest (5 is closest to plasma membrane)

Question 9

what are lysosomes

Answer 9

• membrane bound organelle
• contain digestive enzymes (therefore needs to be enclosed)
• Denature and degrade proteins, nucleic acids, carbohydrates, lipids etc.
• membrane bound
• about pH 5

Question 10

what are endosomes

Answer 10

• membrane-bound vesicles, formed via endocytosis from plasma membrane
• regulate trafficking of proteins and lipids among other subcellular compartments of the secretory and endocytic pathway
• 3 types of endosomes:
  
  1. early endosomes:
     
     • fromed by endocytosis
     • Receive endocytic vesicles from plasma membrane
     • main sorting sites on the endocytotic pathway
  2. late endosomes:
     
     • formed from maturation of early endosomes
     • sort cargo for transport to lysosomes and golgi apparatus
  3. recycling endosomes: trasport cargo back to plasma membrane
• dragram:
  
  • endocytic pathway green
  • secretory pathway red
  • retrieval pathway (things get sent back to where they are from) blue

Question 11

what is endocytosis

Answer 11

• process by which extracellular materials are internalised into the cell
• plasma membrane surrounds such materials, invaginates and budds off into the cytosol

Question 12

what is the secretory pathway

Answer 12

• pathway by which the cell secretes proteins into the extracellular environment
• consists of endoplasmic reticulum, Golgi apparatus and the vesicles that travel in between them as well as the plasma membrane, and lysosomes

Question 13

what are peroxisomes

Answer 13

• membrane bound organelle
• oxidative reactions which break down various substrates:
  
  • oxidation of fatty acids provides metabolic energy
  • oxidation of toxic substrates such as alcohol
• Contains catalase to decompose hydrogen peroxide produced in oxidative reactions. The hydrogen peroxide is either converted into water or used to oxidise other organic substrates.

Question 14

what are chloroplasts

Answer 14

• double membrane bound
• photosynthesis
• has its own DNA and ribosomes to synthesise some of its proteins

Question 15

what are mitochondria?

Answer 15

• double membrane bound
• respiration
• has its own DNA and ribosomes to synthesise some of its proteins

Question 16

what are ribosomes

Answer 16

• fromed by assembly of rRNAs and proteins
• facilitate mRNA translation = protein synthesis