Chapter 17 Flashcards
Gene expression
Process by which DNA directs protein synthesis
How does RNA’s structure differ from DNA’s?
- Sugar is ribose instead of deoxyribose
- Single stranded
- Uracil instead of Thymine
- Nonhelical
Why must only eukaryotic pre-mRNA go through RNA process?
It must pass through the nuclear envelope
Primary trasnscript
Initial RNA transcript from a gene (pre-mRNA)
What does RNA polymerase do?
- Pries DNA strands apart
- Hooks RNA nucleotides together
What is the stretch of DNA that is transcribed?
Transcription unit
Where does the RNA polymerase attach to to start initiation?
Promoter
What is the TATA box?
Stretch of nucleotides in the promoter region
What do transcription factors do?
Bind to promoter to signal RNA polymerase to come over to the promoter
What signals RNA polymerase to bind to the promoter?
Transcription factors
What does the transcription initiation complex consist of?
RNA polymerase II and transcription factors
How does DNA reallign so quickly after RNA polymerase transcribes the template strand?
Previous RNA stretches peel away
What happens in termination for eukaryotes?
RNA strand is cut from the polymerase that continues to transcribe past the DNA strand
What three things occur in RNA processing?
- Introns are cut away
- 5’ cap is added
- Poly-A tail is added
What are the functions of the 5’ cap and poly-A tail?
- Facilitate export of mRNA
- Protect mRNA from hydrolytic enzymes
- Help ribosomes attach to 5’ end
Introns
Noncoding sequences between coding sequences
What does RNA splicing do?
Removes introns and joins exons
What do spliceosomes consist of?
small sibonucleicproteins (snRNP) and proteins
Spliceosomes are a type of what?
Ribozyme
Ribozyme
RNA molecule that functions as an enzyme
What performs RNA splicing?
Spliceosomes
What properties of RNA allow it to function as an enzyme?
- Can form 3D shape from ability to pair with itself (specific structure)
- Some bases in RNA contain functional groups
- May hydrogen bond with other nucleic acid molecules (adding specificity)
What is alternative RNA splicing?
Fact that some genes can form different polypeptide types depending on which parts are treated as exons during splicing
Why can the number of different proteins an organism can produce be larger than its number of genes?
Alternative RNA splicing
Domains
Discrete regions of proteins
How can exon shuffling result in new proteins?
Introns provide more area for crossover of exons
What are ribosomes made up of?
Proteins and ribosomal RNA (rRNA)
What are the three binding sites of ribosomes?
E site, P site, A site
What is the start codon that the small ribosomal subunit stops at?
AUG
What is the initiator tRNA carrying to pair with codon AUG?
Methionine
What brings the large subunit the complete the translation initiation complex?
Initiation factors
What does the translation initiation complex consist of?
Both ribosomal subunits, mRNA, initial tRNA
In translation, protein factors aid in each of the three processes. Which factors are used in each and how?
- Initiation: initiation factors bring in large subunit
- Elongation: elongation factors help to add amino acids in polypeptide chain
- Termination: release factors hydrolyze polypeptide chain
When does termination in translation occur?
When a stop codon in mRNA reaches the A site
When stop codon in the mRNA reaches the A site what happens?
Release factor accepted at A site to hydrolyze bonds and split polypeptide
Polyribosome
String of ribosomes translating 1 strand of mRNA at the same time
How are polypeptides usually made functional after translation?
- Polypeptide chains modified
2. Completed proteins sent to specific sites
WHat are some types of post-translational modifications?
- Enzymes cleave polypeptides
- Polypeptides come together
What are the 2 types of ribosomes?
Free and bound
Free ribosomes make proteins for/that ___, bound ribosomes make proteins for ____
- that function in cytosol
- for endomembrane system/for secretion
What are polypeptides destined for ER/secretion marked by?
Signal peptide
A signal peptide calls for what to bring the ribosome to the ER?
Signal-reception particle (SRP)
Mutation
Change in genetic material of a cell or virus
What are the 2 categories of point mutations
- Substitutions
2. Insertions/deletions
What are the 3 types of point mutation substitituions?
- Silent mutation creates the same amino acid
- Missense mutation still codes for amino acid
- Nonsense mutation changes amino acid codon to stop codon
What are frameshift mutations?
Alteration of reading frame from insertion/deletion
How can mutations arise?
- Spontaneously during DNA replication, recombination, or repair
- From mutagens
