Nucleotides and Nucleic Acids Overview

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Questions and Answers

What is the role of nucleoside 5'-triphosphates in metabolism?

They facilitate cellular communication.

They act as enzymes.

They are structural components of nucleic acids.

They serve as energy carriers. (correct)

Which nucleoside triphosphate is primarily involved in carbohydrate metabolism?

CTP

UTP (correct)

GTP

ATP

What type of bond forms between nucleotides in a nucleic acid chain?

Hydrogen bonds

Covalent bonds

3',5'-Phosphodiester bridges (correct)

Ionic bonds

Which process is primarily linked with the action of ATP?

Energy metabolism Signup and view all the answers

What is a common function of cyclic nucleotides?

They are involved in signal transduction. Signup and view all the answers

Which of the following is NOT a direct function of nucleoside 5'-triphosphates?

Serving as structural components of cells Signup and view all the answers

What characterizes the structure of DNA as compared to RNA?

Deoxyribose sugar versus ribose sugar Signup and view all the answers

Which type of RNA is responsible for carrying the message for protein synthesis?

Messenger RNA Signup and view all the answers

Which of the following statements accurately describes nucleic acids?

Nucleosides consist of a base bonded to a sugar. Signup and view all the answers

What is the complementary DNA sequence for the segment ATCGGCTAAGC written in the 3′-to-5′ direction?

TAGCCGATTCG Signup and view all the answers

Erwin Chargaff's observations indicated which of the following relationships in DNA?

The A:T ratio is nearly 1:1 across various organisms. Signup and view all the answers

Which statement about the base pairs in DNA is true?

Base pairs have essentially the same shape when paired correctly. Signup and view all the answers

What is the effect of hydroxide ion (OH-) on the C'2 hydroxyl group during RNA hydrolysis?

It abstracts a proton, resulting in a charged oxygen. Signup and view all the answers

What is a major factor contributing to the stability of the DNA double helix?

Hydrophobic effects from stacked base pairs. Signup and view all the answers

What is a product of the hydrolysis of RNA following the creation of a cyclic nucleotide?

It results in the hydrolysis into 2’ and 3’-monophosphate derivatives. Signup and view all the answers

Which of the following statements regarding RNA and DNA sugars is correct?

RNA contains ribose, while DNA contains deoxyribose. Signup and view all the answers

Which statement correctly describes semiconservative replication of DNA?

Each new helix contains both parental strands. Signup and view all the answers

Which statement about the direction nucleic acids are written in is false?

Nucleic acids are written in the 3′-to-5′ direction. Signup and view all the answers

What role do van der Waals forces play in DNA structure?

They contribute to the stability through base stacking. Signup and view all the answers

What role does DNA polymerase play in DNA synthesis?

It catalyzes the formation of phosphodiester bridges. Signup and view all the answers

What direction does chain elongation proceed during DNA synthesis?

5'-to-3' direction. Signup and view all the answers

What activity do many DNA polymerases possess to ensure accuracy during synthesis?

Activity to detect mismatched nucleotides and remove them. Signup and view all the answers

How do some viruses replicate their RNA genomes?

With the help of RNA-directed RNA polymerases. Signup and view all the answers

What is the primary role of transfer RNA (tRNA) in gene expression?

To carry amino acids to the ribosome for peptide-bond formation Signup and view all the answers

Which statement accurately describes the function of ribosomal RNA (rRNA)?

It catalyzes the formation of peptide bonds Signup and view all the answers

Which of the following accurately identifies the result of the transcription process?

Synthesis of messenger RNA (mRNA) from DNA Signup and view all the answers

What is the main requirement for RNA polymerase to synthesize RNA?

Double-stranded or single-stranded DNA template Signup and view all the answers

What distinguishes retroviruses from other types of viruses?

They convert single-stranded RNA to DNA Signup and view all the answers

Which RNA type is most abundant in E.coli, according to the relative amounts provided?

Ribosomal RNA (rRNA) Signup and view all the answers

In what direction does RNA synthesis occur?

5′ to 3′ direction Signup and view all the answers

What does reverse transcriptase specifically do in retroviruses?

Converts RNA into DNA Signup and view all the answers

What drives the synthesis of RNA during elongation?

Pyrophosphate hydrolysis Signup and view all the answers

If the DNA template strand is 3'–TCAAGGCGA–5', what is the resulting mRNA sequence?

5'–AGUUCCGCU–3' Signup and view all the answers

What characterizes the promoter sites for transcription?

Where RNA polymerase binds to initiate transcription Signup and view all the answers

What is the role of the terminator sequence in transcription?

To signal the end of transcription Signup and view all the answers

Which of the following best describes the structure of the terminator sequence in prokaryotes?

A stem-loop structure followed by U residues Signup and view all the answers

Which sequence is a common promoter element in eukaryotes?

CAAT box Signup and view all the answers

How does RNA polymerase recognize where to start transcription?

Through interaction with promoter sites Signup and view all the answers

What is the significance of the base composition found in newly synthesized RNA?

It complements the DNA template strand Signup and view all the answers

Study Notes

Nucleoside 5'-Triphosphates Are Carriers of Chemical Energy

Nucleoside 5'-triphosphates are critical for metabolism due to their high-energy phosphoric anhydride bonds
The bases in nucleotides serve as recognition units
Cyclic nucleotides act as signal molecules and regulators of cellular processes
ATP is essential for energy metabolism
GTP drives protein synthesis
CTP drives lipid synthesis
UTP drives carbohydrate metabolism

The Structure of a Nucleic Acid Chain Can Be Simplified

Nucleic acid chains are represented by the sequence of their bases

3',5'-Phosphodiester bridges link nucleotides together to form polynucleotide chains.

The 5'-ends of the chains are at the top; the 3'-ends are at the bottom.

What Are the Different Classes of Nucleic Acids?

DNA exists in one form and has one primary purpose
RNA exists in three (or four) types and has three (or four) purposes
- Ribosomal RNA (rRNA) forms the structural and functional basis of ribosomes
- Messenger RNA (mRNA) carries the genetic code for protein synthesis
- Transfer RNA (tRNA) carries amino acids to the ribosomes for protein synthesis
- Other types include small nuclear RNA and small non-coding RNAs

The Structure of DNA

Each phosphodiester bridge in a nucleic acid backbone has a negative charge
Nucleosides consist of a base bonded to a sugar
DNA contains the bases adenine (A), thymine (T), guanine (G), and cytosine (C)
Nucleic acids are conventionally written in the 5'-to-3' direction

Base Pairing in DNA

Guanine pairs with cytosine (G:C)
Adenine pairs with thymine (A:T)
The base pairs have similar shapes
Hydrogen bonds hold the base pairs together

Chargaff's Rules

The A:T and G:C ratios are nearly 1:1 in different organisms
The A:G ratio varies between organisms

Stability of the Double Helix

Base stacking contributes to the stability of the double helix due to hydrophobic interactions
Van der Waals forces also stabilize stacked base pairs

DNA Replication

DNA replication involves the unwinding of the double helix and separation of the two strands
Each strand serves as a template for the synthesis of a new complementary strand
DNA polymerase catalyzes the addition of nucleotides to the growing strand in a 5'-to-3' direction
The process is semiconservative, meaning that each new helix contains one parental strand and one newly synthesized strand

RNA

RNA is less susceptible to hydrolysis by dilute base than DNA due to its shorter glycosidic bond
Hydrolysis of RNA by dilute base involves:
- An OH- abstracts a proton from the C'2 hydroxyl group
- The charged oxygen attacks the positive phosphorus, breaking the phosphodiester bond
- The cyclic nucleotide is hydrolyzed by water to form a mixture of 2'- and 3'-monophosphate derivatives

Gene Expression

Gene expression is the process of converting genetic information from DNA into functional molecules
It involves two steps:
- Transcription: DNA is transcribed into mRNA
- Translation: mRNA is translated into proteins

Types of RNA

Messenger RNA (mRNA): serves as a template for protein synthesis
Transfer RNA (tRNA): carries amino acids to the ribosome for protein synthesis
Ribosomal RNA (rRNA): forms the major component of ribosomes and acts as a catalyst for protein synthesis

RNA Polymerase

RNA polymerase synthesizes RNA from a DNA template
It does not require a primer
The process involves the elongation of the RNA strand in a 5'-to-3' direction using ribonucleoside triphosphates (ATP, GTP, UTP, and CTP)
The reaction is driven by pyrophosphate hydrolysis

Transcription

Transcription begins at promoter sites and ends at terminator sites
Promoter sites are regions on DNA that bind RNA polymerase and determine the start of transcription
Terminator sequences are regions that signal the end of transcription

Promoter Sites

Prokaryotes: Pribnow box (-10 region), -35 region
Eukaryotes: TATA box (Hogness box), CAAT box

Transcription Termination

Prokaryotes: terminator sequences or rho protein
Eukaryotes: less well-defined, may involve specific sequences or protein factors
Terminator sequences often involve a stem-loop structure followed by a sequence of U residues

Complementarity Between DNA and RNA

The base sequence of mRNA is complementary to the template strand of DNA
Uracil (U) in RNA replaces thymine (T) in DNA

Key Characteristics of DNA Synthesis

Requires four deoxynucleoside 5'-triphosphates and Mg2+
Occurs on a pre-existing DNA template
Requires a primer to initiate synthesis
Chain elongation proceeds in the 5'-to-3' direction
Many DNA polymerases have nuclease activity to remove mismatched nucleotides

Viral RNA Genomes

Some viruses have RNA genomes that are replicated by RNA-directed RNA polymerases
Retroviruses have single-stranded RNA genomes that are converted to DNA by reverse transcriptase

Hypochromism

Hypochromism is the decrease in UV absorbance at 260 nm when DNA is in a double-stranded form
This phenomenon is due to stacking interactions between base pairs
It is an indication of the double helix formation

X-Ray Diffraction of DNA

X-ray diffraction studies provided essential information about DNA structure
They revealed that DNA is a double helix with a helical structure

Importance of Chargaff's Discovery

Chargaff's discovery of the equivalence of A and T, and G and C, was essential for understanding DNA structure
It supported the idea of base pairing in DNA and provided evidence for the Watson-Crick model

Semiconservative Replication

DNA replication is semiconservative, meaning each new DNA molecule contains one parental strand and one newly synthesized strand

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Description

Explore the vital role of nucleoside 5'-triphosphates in metabolism and their function as energy carriers. This quiz delves into the structure of nucleic acid chains, the significance of phosphodiester bridges, and the classes of nucleic acids including DNA and RNA. Test your knowledge on these essential biomolecules.