Chapter 7 Learnsmart

Organize the steps that are involved in the mechanism of RNA interference (RNAi).

1. Cell produces short single-stranded RNA 2. An RNA-induced silencing complex (RISC) assembles 3. Binding of the RNA in the RISC to mRNA tags the mRNA for destruction 4. Enzymes cut mRNA; RISC can then bind to another molecule

Please place the following events in transcription in the correct order.

1. RNA polymerase binds to the promoter region just upstream of the gene. 2. RNA polymerase unwinds the DNA at the promoter site and begins to transcribe the template strand of DNA. 3. RNA polymerase moves along the template strand of DNA adding complementary RNA nucleotides, extending the mRNA. 4. Transcription continues until a terminator site in the DNA is reached. 5. The mRNA transcript is released.

Inducible enzyme

Not routinely produced at significant levels, but their synthesis can be turned on when needed. These are often used in the transport and breakdown of specific energy sources.

When a repressor binds to the operator site on DNA,

it blocks RNA polymerase binding and mRNA synthesis.

When a bacterium is grown on glucose only,

it must synthesize all the amino acids it needs.

In an inducible operon, when a substrate or inducer is present,

it reacts with the repressor and inactivates it

Transcription begins when RNA polymerase binds to the

promoter on DNA

In some degradative pathways, in the absence of an inducer (such as arabinose),

the activator protein can't bind to DNA, and RNA polymerase can't bind to the promoter site.

When an amino acid such as arginine binds to a repressor,

the repressor binds to the operator site

The process of transcription is similar to

the synthesis of the leading strand during DNA replication.

Which nucleotide is not found in RNA?

thymine

Arrange the following proteins in the correct order in which they participate in DNA replication. 1 = Primase 2 = Helicase 3 = DNA ligase 4 = DNA polymerase

2, 1, 4, 3

If a 75 base-pair fragment of DNA has 25 cytosines in it, how many adenines would you expect it to have?

50

operons

Coordinated sets of genes that are regulated as a single unit

True or false: RNA pol can only add to an existing nucleotide sequence

False

Why is translation needed?

The subunits of nucleic acids are nucleotides, while those of proteins are amino acids.

True or false: Replication, transcription and translation take place in the bacterial cytoplasm.

True

A(n) ______ is a cluster of genes that perform related functions, found in ______.

operon, prokaryotes

Transcription is often controlled by DNA-binding proteins. A(n) ______ is a regulatory protein that blocks transcription, while a(n) ______ is a regulatory protein that facilitates transcription.

repressor, activator

A mechanism that blocks transcription

will block the production of mRNA

If the codon GGU is positioned in the A site of the ribosome, which of the following will occur?

A tRNA with the anticodon CCA will deliver its amino acid to the site. Correct

If an organism lost the ability to make primase, what would it be unable to do?

Add a short sequence of complementary RNA to the existing DNA strand. Correct

Introns are removed and exons are spliced together

Before translation

True or false: The purpose of RNA synthesis is to provide a new copy of DNA as the original strand deteriorates over time.

False

Which of the following statements regarding bacterial gene control is FALSE?

Genes for constitutive enzymes can be turned on and off as necessary.

Please select the statements that are true of inducible operons to test your understanding of the differences between inducible and repressible operons.

Inducible operons are usually in the "on" state and are 'turned off' when not needed. The inducer is often the product of the enzyme that is encoded.

What role does the sigma factor of RNA polymerase have in transcription?

It recognizes and binds to the promoter region of the template DNA.

DNA in cells can encode for thousands of different proteins. Why do cells require mechanisms to regulate expression of the genes that code for these proteins?

Not all proteins are needed at all times, or in equal amounts. Regulating their expression saves energy and time.

The initial transfer RNA occupies the _____ site on the ribosome.

P site

Translation of mRNA into protein begins before transcription is complete in ______.

Prokaryotes only

Which of the following is not involved in the initiation of translation?

RNA pol

Constitutive enzyme

Synthesized constantly, these enzymes usually play a critical and indispensable role in central metabolic pathways.

What happens when a hairpin loop forms in mRNA?

The RNA polymerase and the mRNA dissociate from the DNA.

What component of RNA is different from one person (or one bacterium) to the next?

The order of nitrogenous bases.

If one strand of DNA contains the bases ACAGT, what would be the complementary bases on the mRNA strand?

UGUCA

in the absence of lactose,

a repressor protein binds to the operator.

In the absence of lactose, the lac repressor is

active and can bind to the operator

The lac operon is expressed when

glucose is low and lactose is present

Synthesis of mRNA is

in the 5' to 3' direction with new nucleotides being added to the 3' end of the mRNA molecule.

RNA polymerases:

synthesize chains of ribonucleotides synthesize molecules shorter than the chromosome

Two different mechanisms for copying the DNA strands are used because

The strands are oriented in opposite directions

Which of the following statements about translation are CORRECT?

The three potential reading frames found on mRNA generally code for the same amino acid. One codon can code for two different amino acids.

Repressible enzyme

These are produced routinely, but their synthesis can be turned off when they are no longer required. These are generally used in anabolic (biosynthetic) pathways.

Binding of an activator to an activator binding site on DNA

enhances the ability of RNA polymerase to bind to the promoter site.

RNA interference (RNAi) is a mechanism by which

eukaryotic cells destroy RNA transcripts in a selective and specific manner to control gene expression.

True or false: Eukaryotic mRNA usually specifies multiple proteins.

false