Nucleus and Protein Synthesis Flashcards
Briefly describe the process of DNA transcription.
(a) Initiation: Transcription begins when RNA polymerase binds to a promoter region near the beginning of a gene. The promoter often contains a TATA box, a sequence rich in adenine (A) and thymine (T) bases.
(b) Transcription Factors: RNA polymerase requires the assistance of transcription factors to recognize and bind to the promoter region. One such transcription factor is the TATA-binding protein (TBP), which specifically recognizes the TATA box.
(c) Opening the Helix: Upon binding, RNA polymerase, along with transcription factors, causes the DNA strands to unwind, forming a transcription bubble.
(d) Elongation: RNA polymerase moves along the DNA template strand, synthesizing a complementary RNA strand by adding RNA nucleotides in the 5’ to 3’ direction.
(e) Termination: The process ends when RNA polymerase encounters a termination signal, leading to the release of the newly synthesized RNA molecule.
Where is rRNA synthesized?
nucleolus
Name two purines and three pyrimidines. (Remember: Purines are two-carbon nitrogen ring bases while pyrimidines are one-carbon nitrogen ring bases.)
purines: adenine and guanine
pyrimidines: cytosine, thymine, uracil
What is pre-mRNA?
This is the primary transcript from a protein coding gene and contains both introns and exons.
What is small nuclear RNA? (snRNA)
This is a type of RNA that directs the splicing of pre-mRNA to form mRNA.
Further notes:
The primary function of snRNA is in the processing of pre-messenger RNA in the nucleus. They play a critical role in the splicing of pre-mRNA, which is the process by which introns, or non-coding sequences, are removed from pre-mRNA transcripts, and exons, or coding sequences, are joined together to form mature messenger RNA (mRNA).
Which type of RNA carries genetic code to the cytoplasm for controlling the type of protein formed?
mRNA
What is ribosomal RNA (rRNA)?
rRNA, along with proteins, forms the ribosome.
What are microRNAs (miRNAs)?
These are single stranded RNA molecules of 21 to 23 nucleotides that regulate gene transcription and translation.
*Side note: siRNAs (silencing RNA/short interfering RNA) are synthetic miRNAs and can be administered to silence expression of specific genes.
What is a polyribosome?
This is a cluster of ribosomes attached to one mRNA.
Which enzyme facilitates formation of peptide bonds between successive amino acids during translation?
peptidyl transferase
State two methods whereby biochemical activities in the cell are controlled.
- genetic regulation: degree of activation of the genes and the formation of gene products are themselves controlled
- enzyme regulation: activity levels of already formed enzymes in the cell are controlled
Each active ribosome has 3 different binding sites for tRNA molecules: ____(1)____, which holds the tRNA which is linked to the growing polypeptide chain; the ____(2)____ which holds the tRNA bringing the next amino acid to be added to the chain; and the ____(3)____, which releases the tRNA molecules back into the cytoplasm.
Further notes:
tRNA serves as an adaptor molecule that translates the genetic code from mRNA into the amino acid sequence of proteins. It carries specific amino acids to the ribosome, where proteins are synthesized. Each type of tRNA is specific to one amino acid and recognizes one or more codons for that amino acid on the mRNA through its anticodon.
tRNA molecules have a characteristic cloverleaf structure with several important regions:
(a) Anticodon loop: contains a set of three nucleotides that are complementary to the codon on the mRNA.
(b) Acceptor stem: the 3’ end of the tRNA where the corresponding amino acid is attached.
(c) D-arm and T-arm: these are additional structures that help stabilize the tRNA and aid in its recognition by the correct aminoacyl-tRNA synthetase.
Before tRNA can deliver an amino acid, it must be “charged” with the correct amino acid by an enzyme called aminoacyl-tRNA synthetase. This enzyme ensures the correct pairing of tRNA with its corresponding amino acid. [Diagram]
Termination of protein synthesis: “A protein called a ________ binds to the exposed A site causing the polypeptide to separate from the remaining tRNA molecule.”
release factor
- What are the three stop codons?
- What is the start codon and which amino acid does it encode for?
- UAA, UAG, UGA
- AUG, methionine
What are mutations?
They are changes in the nucleotide sequence of DNA and can either by genetic/hereditary or acquired/somatic.
(Note that many mutations are repaired by enzymes.)
Under causes of mutations, there are mutations that are spontaneous and there are those that are induced. Briefly state how each of the 2 are caused.
a) Spontaneous mutations are caused during DNA replication/incorporation of incorrect nucleotide into growing DNA chain.
b) Induced mutations are caused by changes in DNA brought about by some environmental factors e.g. mutagens such as chemicals, smoking and exposure to radiation.
List the classifications of types of mutations.
- Genome mutation
- Gene mutations (change in nucleotide sequence of a gene)
- Chromosomal mutation
List the types of gene mutations.
- Point mutation - single nucleotide base may be substituted by a different base
- Insertion
- Deletion
Why are insertion and deletion during gene mutations known as frame shift mutations?
This is because they lead to alterations in the reading frame of the DNA strand.
What are snRNPs? What is their role in transcription?
snRNPs (small nuclear ribonucleoproteins) are composed of snRNA (small nuclear RNA) and proteins. They work together in the spliceosome to catalyse the removal of introns and joining of exons in pre-mRNA strands.
Side note: What is a spliceosome?
A spliceosome is a large ribonucleoprotein complex found primarily within the nucleus of eukaryotic cells. It is assembled form snRNAs and numerous proteins. The spliceosome catalyses the removal of introns, and the ligation of flanking exons.
Redundancy of the genetic code occurs during which step of protein synthesis?
The genetic code is degenerate, meaning that multiple codons can code for the same amino acid. This redundancy allows for flexibility and protection against mutations. This redundancy occurs during the translation step of protein synthesis.
What process initiates protein synthesis?
Translation. During translation, the genetic information stored in the messenger RNA (mRNA) is decoded to synthesize a protein. The process of translation begins with the binding of the small ribosomal subunit to the mRNA molecule, followed by the recruitment of the initiator transfer RNA (tRNA) molecule that carries the amino acid methionine. The large ribosomal subunit then joins the complex, and the process of elongation begins.
A researcher made an interesting observation about a protein that was translocated into the rough endoplasmic reticulum (ER) during its synthesis and eventually ending up in the plasma membrane. Significantly, the protein in the plasma membrane was found to be slightly larger than the cognate protein in the ER. The protein was probably changed in the
Select one:
a. smooth endoplasmic reticulum
b. mitochondrion
c. Golgi apparatus
d. lysosome
e. nucleus
Choice C.
The Golgi apparatus is known for its role in modifying, sorting, and packaging proteins for transport to various locations within the cell, including the plasma membrane. As proteins move through the Golgi apparatus, they can undergo a variety of modifications such as glycosylation (the addition of sugar groups), which can increase the size of the protein. Therefore, the observation that the protein in the plasma membrane is slightly larger than the protein in the ER suggests that it may have been modified in the Golgi apparatus.
What’s a cognate protein?
In the context of molecular biology, a “cognate protein” typically refers to a protein that has a specific, known, and validated relationship with another biomolecule. This could be a receptor and its cognate ligand, or a tRNA and its cognate amino acid. In other words, it’s about proteins that are meant to interact with each other in a functional complex. The term “cognate” is borrowed from linguistics, where it signifies a correspondence or relation. So, when we talk about a “cognate protein”, we’re referring to a protein that corresponds to, or is related to, another specific molecule in a meaningful way.
