Gene Expression Flashcards
What is gene expression?
The process by which DNA is used to synthesize a functional product (e.g., a protein).
What is the central dogma of molecular biology?
DNA → RNA → Protein (transcription & translation).
What is the difference between genotype and phenotype?
Genotype = inherited genetic information. Phenotype = observable traits influenced by genotype and environment.
What are the three key stages of gene expression?
- Transcription (DNA → RNA), 2. RNA Processing, 3. Translation (RNA → Protein).
What is transcription?
The process of synthesizing RNA from a DNA template.
What are transcription factors?
Proteins that bind to the promoter region to help initiate transcription.
What is the promoter region?
A DNA sequence where RNA polymerase and transcription factors bind to start transcription.
What are the template and coding strands?
Template strand = the DNA strand used to synthesize RNA. Coding strand = the DNA strand that has the same sequence as the RNA (except T → U).
What happens during transcription initiation?
- TATA box (in promoter) is recognized. 2. Transcription factors bind to the TATA box. 3. RNA Polymerase II binds, forming the transcription initiation complex. 4. Transcription starts.
How does RNA polymerase move along DNA?
RNA polymerase moves 3’ to 5’ along the template strand, synthesizing RNA 5’ to 3’.
What happens during transcription elongation?
RNA polymerase adds RNA nucleotides to the 3’ OH of the growing RNA strand, forming phosphodiester bonds.
What happens during transcription termination?
- The polyadenylation signal (AAUAAA) is transcribed. 2. Nuclear enzymes release pre-mRNA. 3. RNA polymerase II dissociates from DNA.
What is pre-mRNA processing?
Modifications that turn pre-mRNA into mature mRNA before it leaves the nucleus.
What are the three main steps of pre-mRNA processing?
- Capping (5’ cap addition), 2. Tailing (Poly-A tail addition), 3. Splicing (removal of introns).
What is capping?
A modified guanine nucleotide is added to the 5’ end of pre-mRNA.
What are the functions of the 5’ cap?
- Protects mRNA, 2. Increases stability, 3. Aids translation, 4. Helps transport through nuclear pores.
What is tailing (Poly-A tail addition)?
50–250 adenine (A) nucleotides are added to the 3’ end of the pre-mRNA.
What are the functions of the Poly-A tail?
- Prevents degradation, 2. Helps nuclear export, 3. Aids in translation initiation.
What is splicing?
Introns (non-coding regions) are removed, and exons (coding regions) are joined together to form mature mRNA.
Why is splicing necessary?
Removes non-coding sequences so only protein-coding information is used during translation.
Where does splicing occur?
In the spliceosome, inside the nucleus.
What is the function of the spliceosome?
Removes introns and joins exons together using RNA-protein complexes.
What happens if splice sites mutate?
It can lead to incorrect splicing, producing faulty or non-functional proteins.
What is alternative splicing?
Different combinations of exons are used to create multiple proteins from a single gene.
What is translation?
The process of converting mRNA into a protein by ribosomes in the cytoplasm.
What are the key components of translation?
mRNA (template), tRNA (transfers amino acids), Ribosomes (protein synthesis site).
What is the role of tRNA?
Carries amino acids and has an anticodon that binds to mRNA codons.
What are the three steps of translation?
- Initiation, 2. Elongation, 3. Termination.
What happens during translation initiation?
- Small ribosomal subunit binds to the 5’ cap of mRNA. 2. Initiator tRNA (carrying Met) binds to the AUG start codon. 3. Large ribosomal subunit attaches, forming the translation initiation complex.
What happens during translation elongation?
- Codon recognition – tRNA binds to the codon in the A site. 2. Peptide bond formation – The growing polypeptide chain moves from the P site to the A site. 3. Translocation – tRNA moves from A → P → E site, then exits.
What happens during translation termination?
- The ribosome reaches a stop codon. 2. A release factor binds instead of tRNA. 3. The polypeptide is released and the ribosomal subunits dissociate.
What is the ribosome’s structure?
- Small subunit: Binds mRNA. - Large subunit: Has A site (acceptor site), P site (polypeptide site), E site (exit site) for tRNA.
What is the Wobble Hypothesis?
There are 64 codons but only ~40 tRNAs because one tRNA can pair with multiple codons due to flexible base-pairing at the third codon position.
Why is gene expression regulated?
To ensure proteins are made at the right time, in the right place, and in the right amount for spatial and temporal control.
How is gene expression regulated?
- Transcription factors assemble correctly. 2. DNA must be accessible for transcription. 3. mRNA modifications (splicing, polyadenylation). 4. mRNA stability affects how long translation occurs. 5. Regulatory proteins can prevent translation.
What are housekeeping proteins?
Proteins that are constantly produced because they are always needed (e.g., tubulin).
What is cell signaling’s role in gene expression?
Receptor activation → signal transduction → transcription activation → protein synthesis.
What is post-translational modification?
Modifications to proteins after translation to make them functional.
What are some types of post-translational modifications?
- Phosphorylation (adds phosphate), 2. Methylation (adds methyl group), 3. Acetylation (adds acetyl group), 4. Carboxylation (adds carboxyl group), 5. Glycosylation (adds sugars), 6. Cleavage (cuts protein to activate it), 7. Ubiquitination (tags protein for degradation).
Where do post-translational modifications occur?
In the Golgi apparatus or cytosol.
Why are post-translational modifications important?
They regulate protein function, activity, stability, and location.
