IB Biology HL - Unit D1.2: Protein Synthesis

What is protein synthesis?

The process of creating a polypeptide from the instructions in a gene.

What are the two main steps of protein synthesis?

Transcription and Translation.

Where does transcription occur in eukaryotic cells?

In the nucleus.

Where does transcription occur in prokaryotic cells?

In the cytoplasm.

What is the role of messenger RNA (mRNA) in transcription?

It carries the genetic code from DNA to the ribosomes for protein synthesis.

What enzyme is responsible for transcription?

RNA polymerase.

What is the promoter in transcription?

A site on the DNA where RNA polymerase binds to initiate transcription.

What direction does RNA polymerase move along the DNA during transcription?

In the 3' to 5' direction.

What is the antisense strand?

The DNA strand used as a template for mRNA synthesis.

What is the sense strand?

The DNA strand that is nearly identical to the mRNA strand, except for thymine being replaced by uracil.

What is gene expression?

The process by which the information in a gene is used to produce a functional product, usually a protein.

What are transcription factors?

Proteins that help regulate the transcription of genes by binding to the promoter.

What are enhancers?

DNA sequences that increase transcription of a gene when bound by activator transcription factors.

What are silencers?

DNA sequences that decrease transcription of a gene when bound by repressor transcription factors.

What is the role of non-coding DNA?

It plays essential roles in gene regulation and cellular functions, even though it does not code for proteins.

What are exons?

Sequences of DNA that are transcribed and translated into a polypeptide.

What are introns?

Non-coding sequences inside genes that are removed during mRNA processing.

What is the function of telomeres?

To prevent the loss of important coding DNA during replication.

How does alternative splicing relate to introns?

Introns allow for alternative splicing, which can produce different protein variants from the same gene.

What is the significance of the TATA box?

It is a short DNA sequence in the promoter region that is crucial for the initiation of transcription.

What happens at the terminator during transcription?

Transcription stops, and the completed RNA molecule is released.

What is the role of hydrogen bonds in DNA stability?

They provide structural integrity by holding the two DNA strands together.

What is the difference between coding and non-coding DNA?

Coding DNA is transcribed into proteins, while non-coding DNA does not code for proteins but may have regulatory functions.

How do regulatory sequences affect gene expression?

They control when, where, and how much a gene is expressed.

What is the main control point for gene expression?

Transcription.

What is the function of activators in gene regulation?

They increase transcription of a gene by recruiting or stabilizing RNA polymerase.

What is the role of repressors in gene regulation?

They decrease transcription of a gene by blocking RNA polymerase from binding.

What type of RNA is produced during transcription?

Messenger RNA (mRNA).

What are telomeres?

Regions that prevent the loss of important coding DNA during replication.

What happens to telomeres as we age?

They shorten with each round of replication.

What do RNA genes produce?

Functional RNAs, not proteins.

What is the role of rRNA?

It forms the structural and catalytic core of ribosomes.

What is the function of tRNA?

It carries amino acids to the ribosome during translation.

What are the three main post-transcriptional modifications to mRNA?

Addition of a 5' cap, addition of a poly-A tail, and mRNA splicing.

What is pre-mRNA?

The mRNA molecule before post-transcriptional modifications.

What is mature mRNA?

The mRNA molecule after modifications are made.

What is the purpose of the 5' cap?

It prevents degradation of mRNA and enables binding to the ribosome.

What is polyadenylation?

The addition of a long chain of adenine nucleotides to the 3' end of the transcript.

How does the length of the poly-A tail affect mRNA stability?

A longer poly-A tail increases stability and lifespan, while a shorter tail leads to faster degradation.

What is mRNA splicing?

The process of removing introns and joining exons to form mature mRNA.

What are introns and exons?

Introns are non-coding sequences that are removed, while exons are coding sequences that are expressed.

What are snRNPs?

Small nuclear ribonucleoproteins that help cut out introns during splicing.

What is alternative splicing?

The process of removing certain exons to create different polypeptides from a single gene.

What is the first step of protein synthesis?

Transcription, where DNA is used to make mRNA.

What is the second step of protein synthesis?

Translation, where mRNA is used to produce a polypeptide.

Where does translation occur?

At the ribosomes.

What are the two parts of a ribosome?

The small subunit and the large subunit.

What are the three sites on the large ribosomal subunit?

A site (amino acid site), P site (peptide site), and E site (exit site).

What is a codon?

A sequence of three bases on mRNA that codes for a specific amino acid.

What is an anticodon?

A triplet of bases on tRNA that pairs with a complementary codon on mRNA.

What is the average length of mRNA molecules in mammals?

About 2,000 nucleotides.

How many different combinations of bases can be formed in a three-base codon?

64 combinations (4^3 = 64).

What is the maximum number of amino acids that could be coded for with two nucleotides?

16 amino acids (4^2 = 16).

What is the maximum number of amino acids that can be coded for with only 2 nucleotides?

16 amino acids

What are the two key features of the genetic code?

Universality and degeneracy

What does universality in the genetic code mean?

Codons code for the same amino acids in almost all species.

What does degeneracy in the genetic code refer to?

Multiple codons can code for the same amino acid.

Which amino acid is always the first in a polypeptide chain?

Methionine, coded by the start codon AUG.

What are the three stop codons in mRNA?

UAA, UAG, UGA

What is the role of the initiator tRNA during translation initiation?

It binds to the P site of the small ribosomal subunit with methionine.

What is the process of elongation in translation?

The methionine from the initiator tRNA is transferred to the amino acid on the second tRNA, forming a peptide bond.

What happens during translocation in translation?

The ribosomal complex moves down the mRNA strand by three base pairs.

What is the function of the release factor in translation termination?

It signals the end of translation when a stop codon is encountered.

What are post-translational modifications?

Changes that polypeptides undergo to become functional, including cleavage, folding, and addition of chemical groups.

What is a proteome?

The entire set of proteins produced or modified by an organism at a specific time.

Why do cells constantly adjust their proteome?

To manage misfolded proteins, regulatory proteins, and proteins marked for degradation.

What are proteasomes?

Large protein-degrading complexes that break peptide bonds and recycle amino acids.

How are proteins tagged for destruction in proteasomes?

They are tagged with ubiquitin by ligase enzymes.

What happens to proteins once they enter the proteasome?

They are unfolded and threaded through the proteolytic core, where peptide bonds are hydrolyzed.

What is the significance of the third base position in codons?

Mutations in the third base often do not change the amino acid due to degeneracy.

How does the ribosomal subunit recognize the mRNA during translation initiation?

By recognizing the guanine cap placed during post-transcriptional modifications.

What is the role of disulfide bridges in protein structure?

They increase stability between cysteine residues in proteins.

What is the first step in the translation process?

Initiation, where the initiator tRNA binds to the P site of the ribosome.

What occurs during the cleavage of amino acids in post-translational modification?

The polypeptide is converted from a precursor state to its final functional state.

What is the final molecule called after proinsulin undergoes modifications?

Insulin

What happens to the C-peptide during insulin modification?

It is cleaved off after proinsulin passes through the Golgi.

What is the significance of AUG being the first codon in mRNA?

It establishes the start of translation and codes for methionine.

What is the role of the endomembrane system in protein transport?

It facilitates the transport of proteins to their final destination.

What is the relationship between the genome and proteome?

The proteome carries out most cell functions, while the genome contains the genetic information.

What is the process of forming a peptide bond?

A covalent bond formed between two amino acids by dehydration synthesis.

How many amino acids does the human protein titin have?

33,000 amino acids