Chapter 17 Questions Flashcards
Which specific regions of DNA are transcribed?
Genes ?
Which two processes carryout gene expression?
Transcription and Translation
Which two molecules produced because of gene expression are considered “worker” molecules?
RNA and Proteins
Which type of RNA is considered the intermediate between DNA and proteins?
Messenger RNA ?
What are the three main differences between DNA and RNA?
- RNA contains ribose instead of deoxyribose
- RNA is typically single stranded while DNA is usually double stranded
- RNA contains uracil instead of thymine
What are the three types of RNA that are produced by transcription and what specific role does each play during protein synthesis?
- Messenger RNA (mRNA)- contains the code for proteins
- Ribosomal RNA (rRNA)- major component of ribosomes
- Transfer RNA (tRNA)- carries amino acids to ribosomes during protein synthesis
What cellular location does transcription take place in bacteria? What location does translation take place in bacteria?
Since bacteria lack nuclei, they can undergo transcription and translation at the cytoplasm simultaneously
What cellular location does transcription take place in eukaryotes? What cellular location does translation take place in eukaryotes?
transcription occurs in the nucleus, while translation occurs in the cytoplasm
What are the main differences between transcription and translation in bacteria vs. eukaryotes?
Eukaryotes have three different RNA polymerases (one for mRNA, one for tRNA, and one for rRNA) while bacteria only have one RNA polymerase that make all three forms of RNA
What is the strand of DNA that used during transcription called?
Template strand
Which direction does RNA polymerase adds complementary nucleotides to DNA?
5’ to 3’ direction
How can only four DNA nucleotides be used to encode all 20 different amino acids.
since each position in a three nucleotide codon has four possibilities (one for each of the four RNA bases) there are 43 different codons
How many RNA nucleotides make up a codon?
Three
Do some amino acids have multiple codons?
Yes
Know how to add the correct complementary mRNA nucleotides to the template
?
Know how to use the resulting mRNA sequence to encode the correct amino acid sequence using a codon chart
?
What type of mutation leads to a change in the correct reading frame of mRNA?
frame shift mutation
What are the three main stages of transcription and what happens during each stage for both prokaryotes and eukaryotes?
Initiation
Elongation
Termination
What does RNA polymerase recognize and bind to in order to initiate transcription in bacteria?
RNA polymerase itself recognizes and binds to the promoter and initiate transcription
How does initiation of transcription begin in eukaryotes? (i.e. describe the eukaryotic transcription initiation complex)
transcription factors must first bind to a specific sequence in the promoter called the TATA box; the bound transcription factors then recruit RNA polymerase II to bind to the promoter and initiate transcription
During elongation, can multiple RNA polymerase molecules transcribe the same gene at one time?
Yes
What molecule is responsible for separating double stranded DNA during transcription?
RNA polymerase
Which direction does RNA polymerase add complementary nucleotides to the DNA template strand?
5’ to 3’ direction
What is the difference between bacterial and eukaryotic termination?
- In bacteria, the polymerase stops transcription at the end of the terminator sequence and the mRNA can be translated without further modification
- In eukaryotes, RNA polymerase II transcribes the polyadenylation signal sequence (AAUAAA); the pre-RNA transcript is released 10–35 nucleotides past this polyadenylation sequence
- In eukaryotes, the pre-mRNA will then undergo processing prior to being translated; no processing is needed for bacterial mRNA and the mRNA is translated as it is being made
What are the three ways that mRNA is processed after transcription?
- The 5’ end receives a 5’ cap made of a modified guanine nucleotides
- The 3’ end receives a poly A tail made of 50-250 adenine nucleotides
- Introns are removed through RNA splicing
What are the functions of the 5’ cap and poly A tail?
They facilitate the export of mRNA out of the nucleus
They protect mRNA from hydrolytic enzymes
They help ribosomes attach to the 5′ end
Why are introns removed from the primary transcript?
The nucleotide sequences of introns are not used for translation and therefore, must be removed prior to translation
Explain what is involved in the process of intron removal
RNA splicing is a process that removes introns and joins exons to create an mRNA molecule with a continuous coding sequence
What types of special enzymes are used for intron removal?
RNA splicing is carried out by a protein and RNA enzyme complex called a spliceosome
The RNA molecules in the spliceosome are ribozymes
Describe the structure of tRNA molecules:
Single or double stranded?
Two-dimensional vs three dimensional shape?
What are located at each end of tRNA molecules?
- single strand of RNA (~80 nucleotides long)
- tRNA is able to fold upon itself to form a three dimensional structure
- At one end of the tRNA is an amino acid attachment site. At the other end is an anticodon on the other end (the anticodon base-pairs with a complementary codon on mRNA)
What is the name of the enzyme that attaches amino acids to tRNA?
aminoacyl-tRNA synthetase
What does the anticodon on tRNA bind to?
mRNA codon
Can some tRNA bind to multiple codons? Is this an exact complementary match?
There are 61 different amino acid codons, but only 45 different tRNAs; this means that some tRNAs can bind to more than one codon through “wobble” binding
What type of molecules make up ribosomes?
proteins and ribosomal RNA (rRNA)
What are the two ribosomal subunits called?
The two ribosomal subunits (large and small) are made of proteins and ribosomal RNA (rRNA)
How many tRNA binding sites are there on the ribosome and what are they called?
- The P site, the A site, and the E site.
What does the initiation complex consist of?
mRNA, an initiator tRNA , and the two ribosomal subunits
What are the three steps of elongation?
codon recognition, peptide bond formation, and translocation
Describe the process of polypeptide elongation starting with the binding of the initiator tRNA to how amino acids are added to the growing polypeptide chain, to the process of translocation and finally termination.
During elongation, amino acids are added one by one to the growing polypeptide chain
Each addition involves proteins called elongation factors and occurs in three steps: codon recognition, peptide bond formation, and translocation.
Termination occurs when a stop codon in the mRNA reaches the A site of the ribosome
What are the two major ways that polypeptides are processed after being translated?
- Folding
- Post translational modifications (addition of other molecules or functional groups to polypeptide)
Where do proteins synthesized by cytosolic ribosomes function in the cell?
cytoplasm
Where happens to proteins synthesized by ER ribosomes?
Ribosomes bound to the ER make proteins that will go through the endomembrane system to form, secretory proteins, membrane proteins, or proteins that will go to various organelles within the cell (lysosome, mitochondrial, chloroplast, etc.)
