BIOL300: Chapter 7

What is the central dogma of molecular biology?

The process by which DNA is transcribed into RNA, which is then translated into protein.

What are the key chemical characteristics of RNA?

RNA is single-stranded, contains ribose sugar, has uracil instead of thymine, and is unstable/temporary.

How does uracil pair with adenine in RNA?

Uracil binds with adenine through 2 hydrogen bonds, similar to the A-T pairing in DNA.

What is the role of RNA polymerase in transcription?

RNA polymerase unwinds DNA, adds nucleotides to the RNA chain, and forms phosphodiester bonds.

What distinguishes transcription from DNA replication?

Transcription produces shorter RNA strands, while DNA replication duplicates the entire DNA molecule.

What are the differences between eukaryotic and prokaryotic transcription?

Eukaryotes have three types of RNA polymerase and require transcription factors, while prokaryotes use a single RNA polymerase.

What is the function of general transcription factors (GTFs)?

GTFs assemble at the promoter, position RNA polymerase, and help unwind the DNA for transcription.

What is the significance of the TATA box in transcription?

The TATA box is a DNA sequence that helps position transcription factors and RNA polymerase at the promoter.

What is alternative splicing?

A process that allows a single gene to code for multiple proteins by varying the combination of exons included in the mRNA.

What are introns and exons in eukaryotic genes?

Introns are non-coding sequences, while exons are coding sequences that are expressed in the final mRNA.

What is the role of the spliceosome?

The spliceosome, composed of snRNPs, carries out RNA splicing by removing introns and joining exons.

How is mature mRNA recognized for export from the nucleus?

Mature mRNA is marked by a 5' cap and a poly-A tail, which are recognized by proteins that facilitate its export.

What is a codon?

A codon is a sequence of three nucleotides in mRNA that specifies a particular amino acid.

What are the start and stop codons in protein synthesis?

The start codon is AUG (Methionine), and stop codons are UAA, UAG, and UGA.

What is the function of tRNA in translation?

tRNA carries amino acids to the ribosome and matches them to the codons in mRNA.

What is the significance of ribosomes in protein synthesis?

Ribosomes facilitate the translation of mRNA into protein by providing a site for tRNA to bring amino acids.

What happens during the termination of translation?

Release factors bind to stop codons, leading to the release of the newly synthesized polypeptide and disassembly of the ribosome.

How do antibiotics affect protein synthesis?

Many antibiotics inhibit bacterial protein synthesis without affecting eukaryotic protein synthesis.

What is the role of aminoacyl-tRNA synthetases?

These enzymes attach the correct amino acid to its corresponding tRNA, forming a high-energy bond.

What is the purpose of the poly-A tail in eukaryotic mRNA?

The poly-A tail protects mRNA from degradation and aids in the export of mRNA from the nucleus.

What is the difference between the coding potential of prokaryotic and eukaryotic mRNA?

Prokaryotic mRNA can code for multiple proteins, while eukaryotic mRNA typically codes for a single protein.

What is a hybrid RNA/DNA helix?

A transient structure formed during transcription where RNA pairs with the DNA template strand.

What is the significance of the 5' UTR and 3' UTR in mRNA?

The untranslated regions (UTRs) play important roles in the regulation of gene expression.

What is the role of phosphatases in transcription regulation?

Phosphatases dephosphorylate RNA polymerase II, allowing it to bind to DNA and initiate transcription.

What is the function of the 5' cap in eukaryotic mRNA?

The 5' cap protects mRNA from degradation and assists in ribosome binding during translation.

True or false: RNA is always single stranded

False

What is the base the replaces thymine in RNA

Uracil

Is RNA stable or unstable?

unstable

How many bonds are between uracil and adenine?

2

mRNA

codes for proteins

Ribosoomal RNA ( rRNA)

makes up ribosomes

siRNA and miRNA

- Small molecules that bind to mRNA and block translation

- They can bind to, cleave, and degrade mRNA

- Binding to the euchromatin promotes the formation of heterochromatin, preventing transcription

tRNA

transfer RNA; type of RNA that carries amino acids to the ribosome

RNA polymerase II

transcribes mRNA

RNA polymerase I

transcribes rRNA

RNA polymerase III

transcribes tRNA

Start Codon

AUG (methionine)

Bacterial Transcription

initiation, elongation, termination

True or false: one mRNA can code for multiple proteins

True

Eukaryotic RNA polymerase requires accessory proteins called

transcription factors

transcription factors

Collection of proteins that mediate the binding of RNA polymerase and the initiation of transcription.

general transcription factors

. Assemble at promoter

• Position RNA polymerase

• Pull apart the double helix to expose template

• Launch RNA Polymerase

TFIID

the first general transcription factor to bind the promoter, binds to the TATA box through the TATA binding protein (TBP)

3' poly- A - Tail

Poly-A tail - 3' end trimmed at a specific sequence and then a second enzyme

- adds a series of repeated adenine (A) nucleotides to the end

5' capping of mRNA

Phosphate chain at the 5' end

Introns

Noncoding segments of nucleic acid that lie between coding sequences.

Exons

Coding segments of eukaryotic DNA.

spliceosome

RNA splicing carried out by RNA molecules

small nuclear RNAs (snRNAs)

Spliceosomes are composed of _____.

snRNPs and other proteins

Alternative splicing allows for greater protein

diversity

Mature mRNA's are transported to the

cytoplasm. Cap and poly-A tail of mature mRNAs are 'marked' by proteins that recognize these modifications•Once found to be mature mRNA it is exported out of the nucleus

what is a codon

a three-nucleotide sequence that codes for an amino acid

Ribosomes have three sites

E, P, A

What is the E site of a ribosome?

The exit point from the ribosome for the tRNA

What is the P site of a ribosome?

Where a new peptide bond forms

A site of ribosome

holds the tRNA that carries the next amino acid to be added to the chain

What is an anticodon?

the tRNA complement to the mRNA codon