Gene Structure And Expression Flashcards
What is the function of genes?
Genes influence traits by encoding proteins that perform biochemical, cellular, and organismal functions.
What is the Central Dogma of molecular biology?
DNA → RNA → Protein
What is transcription?
DNA is transcribed into RNA by RNA polymerase.
What is translation?
RNA is translated into protein using ribosomes.
What are non-coding RNAs?
Not all genes code for proteins (e.g., rRNA, tRNA); these RNAs have specialized functions.
What components are included in gene structure?
Promoters, exons, and introns (in eukaryotes)
What is the orientation of genes?
5’ → 3’
What is a key difference in gene structure between prokaryotes and eukaryotes?
Prokaryotes lack introns.
What do prokaryotes use for transcription termination?
Simpler termination sequences.
What processes are required for RNA processing in eukaryotes?
Splicing, capping, polyadenylation.
What do eukaryotes use for RNA polymerase binding?
Transcription factors.
What are codons?
Triplets of nucleotides that encode amino acids.
What is the start codon?
AUG (Methionine).
What are the stop codons?
UAA, UAG, UGA.
What is meant by redundancy in the genetic code?
Multiple codons encode the same amino acid due to ‘wobble pairing.’
What are the four types of mutations?
- Silent
- Missense
- Nonsense
- Frameshift
Each type of mutation can affect protein function in different ways.
What characterizes a silent mutation?
No change in protein.
Silent mutations do not affect the amino acid sequence of the protein.
What is a missense mutation?
Amino acid substitution (e.g., sickle cell disease).
Missense mutations can lead to altered protein function.
What happens in a nonsense mutation?
Premature stop codon.
Nonsense mutations can result in truncated proteins.
Define frameshift mutation.
Alteration of the reading frame.
Frameshift mutations can significantly change the resulting protein.
What are the potential impacts of mutations?
Can have evolutionary impacts or cause diseases.
Mutations can influence genetic diversity and disease susceptibility.
What is the first step of transcription in eukaryotes?
Initiation: Transcription factors recruit RNA polymerase to the promoter.
This step is crucial for starting the transcription process.
Describe the elongation phase of transcription.
RNA polymerase synthesizes RNA in 5’ → 3’.
This phase involves the addition of RNA nucleotides complementary to the DNA template.
What occurs during the termination phase of transcription?
Cleavage occurs after the 3’ UTR.
This step marks the end of RNA synthesis.
What is the purpose of 5’ capping in RNA processing?
Stabilizes RNA; recognized by ribosomes.
Capping is essential for mRNA stability and translation initiation.
What is the function of the Poly(A) tail in RNA processing?
Protects RNA from degradation.
The Poly(A) tail enhances mRNA stability and export from the nucleus.
What is the role of splicing in RNA processing?
Removes introns; allows alternative splicing to create diverse proteins.
Alternative splicing can lead to the production of multiple protein variants from a single gene.
What is the first stage of translation?
Initiation: Ribosome assembles on mRNA at start codon
The start codon is typically AUG, which codes for methionine.
What occurs during the elongation stage of translation?
Amino acids added sequentially, reading the mRNA from 5’ to 3’
This process involves tRNA bringing amino acids to the ribosome.
What triggers the termination stage of translation?
Stop codon prompts release of the ribosome
Common stop codons include UAA, UAG, and UGA.
What is the function of the A site on the ribosome?
Accepts new tRNA
The A site is crucial for adding new amino acids during protein synthesis.
What is the role of the P site on the ribosome?
Forms peptide bonds
This site holds the tRNA carrying the growing polypeptide chain.
What happens at the E site on the ribosome?
Releases empty tRNA
The E site is where tRNA exits the ribosome after transferring its amino acid.
What are polysomes?
Multiple ribosomes translating a single mRNA
This allows for efficient and rapid protein synthesis.
What are post-translational modifications?
Folding (chaperones), phosphorylation, glycosylation, lipidation
These modifications can affect protein activity and stability.
What is the main purpose of protein sorting?
Directs proteins to specific cellular locations
This process is essential for maintaining cellular organization and function.
What are sorting signals in proteins?
Specific sequences or structural features that act as ‘postal codes’ for protein targeting
Sorting signals guide proteins to their correct destinations within the cell.
What are signal peptides?
Short amino acid sequences at the N-terminus that direct proteins to the endoplasmic reticulum (ER)
Signal peptides are essential for the initial targeting of proteins during synthesis.
Define Nuclear Localization Signals (NLS).
Short sequences that direct proteins to the nucleus
NLS are critical for the transport of proteins into the nucleus.
What are transit peptides?
Target proteins to organelles like mitochondria or chloroplasts
Transit peptides facilitate the import of proteins into specific organelles.
Where are proteins destined for secretion or membrane synthesized?
In the rough endoplasmic reticulum (ER)
The rough ER is studded with ribosomes, which synthesize these proteins.
How are other proteins synthesized?
In the cytosol and sorted post-translationally
This means that these proteins are synthesized first and then directed to their destinations.
What is the role of a signal recognition particle (SRP)?
Binds the signal peptide on a nascent polypeptide and guides the ribosome to the SRP receptor on the ER membrane
SRP plays a crucial role in initiating protein translocation into the ER.
What occurs during translation into the ER?
The growing polypeptide chain is fed into the ER lumen
This process allows for proper folding and modification of the protein.
What happens to the signal peptide inside the ER?
It is removed by signal peptidase
This step is essential for the maturation of the protein.
What modifications occur inside the ER?
Folding and initial modifications such as glycosylation
These modifications are important for protein functionality and stability.
What is the role of the Golgi apparatus in protein sorting?
Proteins are further modified and sorted for final destinations like the plasma membrane or lysosomes
The Golgi apparatus is a key site for protein processing and distribution.
What directs proteins to specific organelles?
Transit peptides
Transit peptides are short sequences that signal the destination of proteins within the cell.
What role do chaperones play in protein sorting?
Assist in translocation across organelle membranes
Chaperones help proteins fold properly and assist in their transport into organelles.
What is the function of nuclear localization signals?
Allow proteins to pass through nuclear pores
Nuclear localization signals are specific sequences that facilitate the import of proteins into the nucleus.
Is full unfolding of the protein required for passage through nuclear pores?
No
Proteins can pass through nuclear pores without fully unfolding.
What tag is used to send proteins to lysosomes?
Mannose-6-phosphate
This tag is added in the Golgi apparatus and directs proteins to lysosomes for degradation.
What is phosphorylation in the context of protein sorting?
Activates or deactivates sorting signals
Phosphorylation involves adding a phosphate group, which can change a protein’s activity or its interactions.
What role does glycosylation play in protein sorting?
Helps in sorting within the ER and Golgi
Glycosylation is the addition of sugar molecules to proteins, which aids in their proper localization.
What is lipidation’s function in protein sorting?
Anchors proteins to membranes
Lipidation involves the addition of lipid groups to proteins, facilitating their attachment to cell membranes.
Why is protein sorting important for cells?
Maintains cellular compartmentalization
Proper sorting ensures that enzymes and proteins are located where they can function effectively.
What can errors in protein sorting lead to?
Diseases such as cystic fibrosis or lysosomal storage disorders
Mis-sorted proteins can disrupt cellular functions and lead to various health conditions.
