Lesson 6: Transcription and RNA Processing- II

What is pre-mRNA?

aka primary transcriped produced by RNA polymerase

What is RNA guanylyltransferase?

it adds a GMP to the 5' end of the nascent RNA via a 5'-to-5' triphosphate linkage.

What is RNA (guanine-N7) methyltransferase?

this enzyme methylates the guanosine at the N7 position, producing the characteristic m⁷G cap.

What is heterogeneous nuclear RNA?

initial RNA transcript made in eukaryotic cells before processing (aka pre-mRNA)

What is co-transcriptional?

means something happens at the same time as transcription is occurring.

So instead of waiting for RNA to be fully made, certain processes happen while RNA is still being synthesized from DNA. (splicing)

What are the 5’ donor sequence and 3’ acceptor sequence?

intron beginning and end = this loops around and removed the introns

What is the 5’ donor sequence?

(GU) start of intron

What is the 3’ acceptor sequence?

(AG) end of intron

What does the enzyme Poly(A) polymerase (PAP) do?

adds a poly(A) tail to the 3′ end of eukaryotic mRNA after transcription.

What is the spliceosome is a complex made of

snRNA in the nucleus

What is Splicing Co-transcriptional?

Splicing happens while the RNA is still being made

What is lariat?

the looped structure formed when an intron is cut out of pre-mRNA during splicing, “lasso-shaped”

What is the Ribosomal-binding Site?

a short nucleotide sequence on mRNA where the ribosome attaches to start translation. It ensures the ribosome starts protein synthesis at the correct position.

What is the Ribosomal-binding Site in Prokaryotes?

Shine–Dalgarno sequence

What is the Ribosomal-binding Site in Eukaryotes?

5’ cap structure and ribosome scanning mechanism

If things go wrong in the Eukaryotic transcription process, it can result in?

Marfin Syndrome, Systematic lupus, and β-thalassemia (reduced or no beta-globin chains)

The LDL receptor (low-density lipoprotein receptor) gene—often called the lipoprotein B receptor has how many introns and exons?

18 exons and 17 introns

What are Nuclear Pores?

Recognize the 5’ cap and facilitate the export of mRNA into the cytoplasm.

What is mRNA Export?

Exported mRNA enters the cytoplasm where translation occurs

What is Exonucleases?

Degrade polynucleotides by removing nucleotides from the 5’ and 3’ end of strands.

What is 5’ Cap Protection?

Protects mRNA from degradation by 5’ exonucleases.

What is Translation Initiation?

The 5’ cap serves as an important initiating factor for translation in the cytoplasm.

What is Polyadenylation?

process in eukaryotic cells where a poly(A) tail (a long string of adenine nucleotides) is added to the 3′ end of mRNA after transcription.

A polyadenylation sequence (5’-AAUAAA-3’) signals for what?

cleavage site near the 3’ end of the pre-mRNA

Why are there so many introns?

make all genes that we have and allow for alternative splicing to occur

What is alternative splicing?

a process in eukaryotic gene expression where the same pre-mRNA can be spliced in different ways to produce different mature mRNA molecules, so one gene can make multiple proteins

What does the Prokaryotic Ribosome recongnize?

Shine Delgarno sequence

What does the Eukaryotic Ribosome recongnize?

7-Methyl-G Cap

What is the large subunit of the Prokaryotic Ribosome?

50S

What is the large subunit of the Eukaryotic Ribosome?

80S

What is the small subunit of the Prokaryotic Ribosome?

30S

What is the small subunit of the Eukaryotic Ribosome?

40S

What is the total # of subunits for prokaryotic Ribosome?

70S

What is the total # of subunits for eukaryotic Ribosome?

80S

What are Shiga Toxins?

potent bacterial toxins that inhibit protein synthesis in host cells, leading to cell death and tissue damage.

What are Verotoxin?

another name for Shiga toxins

What do Shiga toxins target?

60S (large) subunit of Eukaryotic Ribosome

What is tRNA?

smallest RNA, responsible for translation process

What are the functions of tRNA?

recongnize codon and pick up amino acid

What is the role of the tRNA’s arms?

helps to keep the tRNA stable

Which end of tRNA is phosphorylayted?

5’ end (not added just part of the structure)

What is the Anticodon loop/sequence?

located on the bottom of the tRNA it has the complementary sequence to the mRNA codon

if the mRNA codon: AUG, what is the tRNA codon?

UAC

New amino acids are attached to what part of the tRNA?

3’ end

What sequence does the 3’ end have?

CCA

How many possible codons are there?

64

How many stop codons are there?

3

What is the Start codon in RNA?

AUG

What is the start codon in DNA?

ATG

What type of mutation changes a codon but not the amino acid?

Silent mutation

What type of mutation chnages the codon and amino acid?

Missence muttaion

What type of muttaion results in an early stop?

nonsense mutation

What type of mutation results in a shift in the coding start letters (due to insertion or deletion)

frameshift muttaion

What type of mutation resulted in Sickle cell anemia (Glu → Val)?

Missense Mutation

What type of mutation resulted in Hemophilia?

Nonsense Mutation

What may be a result of a missense mutation?

Improper folding of protein

What may be a result of a silent mutation?

No effect

What may be a result of a nonsense mutation?

truncated (shortened) protein, generally not compatible with life

What is a point mutation?

general term that includes all types of single-base changes

What type of mutation and chnage is resulted from Duchenne MD → Dystrophin?

Deletion causing frameshift

What type of mutation and chnage is resulted from CF (cystic fibrosis) → CFTR?

Deletion Not causing frameshift

What type of mutation and chnage is resulted from Tay-Sachs → hexosaminidase A?

Insertion causing frameshift

What type of mutation and chnage is resulted from Huntington’s Disease → Huntingtin?

Insertion Not causing frameshift

What are five diseases that are a result of Trinucleotide Repeat Expansions?

1. Huntington disease

2. Fragile X syndrome

3. Myotonic dystrophy

4. Spinobulbar muscular atrophy

5. Friedreich’s Ataxia

What type of mutation results in Huntington disease?

Trinucleotide Repeat Expansions

What type of mutation results in Fragile X syndrome?

Trinucleotide Repeat Expansions

What type of mutation results in Myotonic dystrophy?

Trinucleotide Repeat Expansions

What type of mutation results in Spinobulbar muscular atrophy?

Trinucleotide Repeat Expansions

What type of mutation results in Friedreich’s Ataxia ?

Trinucleotide Repeat Expansions

Why must amino acids be activated to make proteins?

Since peptide bond formation is not energetically favorable on its own. The activation step ensures that the reaction is thermodynamically possible.

How many high energy bonds are lost per amino acid?

2

How many aminoacyl-tRNA synthetases are there?

61 differnt ones (unique to each codon)

What enzyme is used to convert tRNA to aminoacyl-tRNA?

some type of aminoacyl-RNA synthetase

What is peptidyl transferase?

a ribozyme

What two parts of the amino acid react to form a peptide bond?

alpha-carboxyl and alpha-amino

What is an amide bond?

another name for a peptide bond