Gene Expression Control Mechanisms

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Questions and Answers

What is the primary function of helicase in the replication process?

To synthesize Okazaki fragments

To initiate the leading strand synthesis

To bind to single-stranded DNA and prevent reactions

To open the parental DNA duplex (correct)

How many primers are required for the leading strand during DNA replication?

Two primers

One primer (correct)

Three primers

No primers needed

What are Okazaki fragments associated with in the context of DNA replication?

Leading strand synthesis

Lagging strand synthesis (correct)

DNA methylation

Single-stranded DNA binding

What is meant by the term 'replichores' in chromosome structure?

The two halves of a chromosome Signup and view all the answers

What role do SSB proteins play during DNA replication?

They bind to single-stranded DNA to stabilize it Signup and view all the answers

What is a distinguishing feature of lagging strand synthesis compared to leading strand synthesis?

It requires multiple primers Signup and view all the answers

What ultimately happens to proteins that bind to single-stranded DNA during eukaryotic replication?

They fall off after completing their function Signup and view all the answers

Which of the following describes the nature of the replication forks in bacterial replication?

They proceed counter-clockwise and clockwise until they meet Signup and view all the answers

What is the primary consequence of preventing DNA methylation during replication?

Blocks replication initiation and leads to increased DNA mutations. Signup and view all the answers

In bacterial replication termination, what role does the tus protein play?

Binds to ter-sites, creating a replication fork trap. Signup and view all the answers

What function does replicative DNA polymerase serve during DNA replication?

It copies both DNA strands and verifies nucleotide accuracy. Signup and view all the answers

What role does RNase H serve in the context of Okazaki fragments?

It removes RNA primers from Okazaki fragments. Signup and view all the answers

What happens when the replication forks meet during termination?

Topoisomerase (Topo 1) is released from the cycle. Signup and view all the answers

What occurs due to the absence of methylation tags during DNA replication?

Original and new DNA strands cannot be differentiated. Signup and view all the answers

What enzyme is responsible for filling in the gaps left between Okazaki fragments?

DNA polymerase Signup and view all the answers

How does co-directionality between transcription and replication benefit bacterial cells?

It helps to minimize accidents between transcription and replication. Signup and view all the answers

Which of the following statements about DNA methylation is correct?

Adenine in GATC sequences is methylated by adenine methyl-transferase. Signup and view all the answers

Which characteristic of the replicative DNA polymerase resembles a hand?

The orientation of its active center. Signup and view all the answers

What is the significance of hemimethylated GATC sites at the origin of replication?

They prevent the origin from being reused until fully methylated. Signup and view all the answers

Which factor is involved in preventing the methylation of hemimethylated GATC sequences?

SegA Signup and view all the answers

Why do unfixed errors accumulate in DNA when methylation is prevented?

Because the mismatch repair mechanism fails to function correctly. Signup and view all the answers

How does DNA methylation assist the DNA mismatch repair (MMR) system?

By allowing the MMR system to distinguish between parent and newly synthesized strands. Signup and view all the answers

What happens to the parental strand during DNA replication in relation to methylation?

It retains methylation, while the new strand remains unmethylated. Signup and view all the answers

What final step is involved in creating a complete DNA strand from Okazaki fragments?

DNA ligase seals the gaps between fragments. Signup and view all the answers

Study Notes

Gene Expression

Seven layers of control occur to form a protein from DNA
Transcriptional control
RNA processing
Transport and localisation
Translational control
RNA degradation
Protein degradation
Protein activation

Control of Gene Expression

DNA is identical in all cells
Differential gene expression allows different types of cells to form
Certain genes function in all cells (e.g., RNA genes, ATPase)
Other genes are only needed in specific tissues
Some genes are temporally regulated (stages of development)
Examples: developmental stages, differentiation stages, cell cycle stages, inducible expression

Transcriptional Control

Transcription factors bind to promoters, guiding and activating RNA polymerase II
Trans-acting factors bind and recognise cis-acting elements
Inducible transcription factors respond to signals (e.g., signalling, hormones)

RNA Processing

Different exon combinations produce tissue-specific protein isoforms
Repressor proteins prevent splicing
Activator proteins cause splicing and shortening of RNA
Alternative polyadenylation affects placement of poly-A tails

mRNA Editing

Different RNA edits occur in different tissues
Deamination of adenine to inosine (A to I) within the introns, alters RNA folding
Deamination of cytosine to uracil, creating a stop codon, is less common

Transport and Localisation

mRNA transported to ER or ribosome
Destination determined by 3' untranslated region (UTR)

Protein Translation

Cis-acting regulatory sequences target trans-acting RNA to regulate mRNA longevity or inhibit translation via microRNA (miRNA)

RNA Degradation

Longer mRNA = more protein
Eukaryotic cells rapidly degrade mRNA via 5' cap removal or 3' degradation

Protein Degradation

Ubiquitin-proteasome pathway degrades proteins
Phosphorylation, unmasking areas of protein that enzymes bind to, influence cleavage and protein stability.

Protein Activity Control (Post-translational)

Cleavage: Removal of amino acids
Inhibitors of protein activity
Binding (e.g., RhoA with actin polymerization)
Transport

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Description

Explore the intricate layers of gene expression control, including transcriptional regulation, RNA processing, and protein activation. Understand how differential gene expression leads to the formation of various cell types and functions. This quiz will cover key concepts related to the control of gene expression in different cellular contexts.