Cellular Processes and Genetic Control Notes

Organelles and Their Functions

• Nucleus: contains DNA
• Free Ribosomes: make proteins to stay in the cytoplasm
• RER (Rough Endoplasmic Reticulum): make proteins headed outside of the cell
• Golgi Apparatus: modifies and packages proteins for export
• SER (Smooth Endoplasmic Reticulum): synthesizes fats, carbohydrates, storage
• Mitochondria: make ATP (adenosine triphosphate)
• Cytoskeleton: provides structural support and transport "rails"
• Lysosomes: digest cellular waste

Basic Functions

• DNA: the instructions for making all proteins in the body.
• mRNA: A copy of a portion of the DNA molecule used as a template for the ribosome to make a protein.
• Ribosomes: An enzyme that actually makes proteins by using the RNA to "read" the sequence of RNA and match to amino acids and piecing them together.
• Genes: portions of the DNA molecule that contain the code for a particular protein.

Protein Synthesis

1. Activation of Transcription Factors:
   • Transcription factors are activated by signaling molecules.
   • These are frequently needed to initiate transcription, or the production of mRNA.
   • Signaling molecules can be lipid-soluble or water-soluble.
     • Lipid-soluble: receptor-ligand complex acts as a transcription factor.
     • Water-soluble: a kinase is activated, which then phosphorylates a transcription factor, activating it.
2. mRNA Formation:
   • An mRNA is formed from the template strand of DNA during transcription.
3. mRNA Modification and Export:
   • The mRNA is then modified a bit and sent out of the nucleus to a ribosome.
4. Ribosome Activity:
   • The ribosome starts at the end of the mRNA and systematically moves down the mRNA molecule.
   • It matches each codon on the mRNA to the appropriate anticodon on a tRNA (transfer RNA).
5. tRNA and Amino Acids:
   • The tRNA is carrying an appropriate amino acid.
   • As the tRNAs are placed against the mRNA, the ribosome makes bonds between the amino acids that the tRNAs bring in.
6. Protein Completion:
   • When the ribosome has linked a tRNA up to every codon on the mRNA, it has made the entire protein.
7. Protein Folding:
   • The protein needs to fold up properly with the help of chaperones.

Protein Production and Packaging

• Proteins Staying in the Cytosol:
  • These proteins are made on free ribosomes in the cytoplasm.
• Proteins Leaving the Cell/Entering Organelles/Membrane Insertion:
  • These proteins are made on the RER and processed through the Golgi apparatus before getting to their final destination.
  • RER Job: to fold and label the proteins for their final destination.
  • Golgi Job: to sort and package the proteins so that they are carried to the correct final destination.
  • Vesicles are created in the Golgi with proteins going to similar destinations: secretion, another organelle, or insertion into the membrane.

Transcription Factors

• A protein that can activate or inhibit the production of an mRNA from a gene.
• These are activated by signals that bind to their receptors.

Quiz Answers

1. Transcription factors:
   • d. Are required for production of most proteins
2. Ribosomes are required for:
   • e. More than one of the above (The bonding of amino acids to one another & The decoding of the mRNA molecule)

True/False

3. Protein synthesis in any cell must begin with the activation of transcription factors.
   • True
4. Proteins that are intended for secretion need to be made on the RER.
   • True
5. Proteins that are going to remain in the cytoplasm are also made on the RER.
   • False
6. All proteins require chaperons to insure proper folding.
   • True