Molecular Biology: DNA and RNA Structure

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Questions and Answers

What role do grooves play in the structure of DNA?

They contribute to the hydrophilic nature of the backbone.

They provide stability to the double helix structure.

They allow the attachment of regulatory proteins. (correct)

They determine the sequence of nucleotides.

How are the two strands of DNA in the double helix arranged?

They are antiparallel, running in opposite directions. (correct)

They are connected by covalent bonds between sugars.

They are formed by a single strand twisted into a helix.

They run parallel to each other in the same direction.

What happens to DNA during denaturation?

Proteins are attached to the nucleotides.

Hydrogen bonds between bases are broken. (correct)

Phosphodiester bonds are cleaved.

The DNA strands rearrange to form a triple helix.

What is the distance between adjacent base pairs in the DNA double helix?

0.34 nm Signup and view all the answers

What distinguishes RNA from DNA in terms of their structure?

RNA contains ribose instead of deoxyribose. Signup and view all the answers

What are the three components of a nucleotide?

Nitrogenous base, pentose sugar, phosphate Signup and view all the answers

Which statement best explains the role of ribosomes in protein synthesis?

They are responsible for translating mRNA into proteins Signup and view all the answers

What distinguishes DNA from RNA structurally?

The type of sugars present in the nucleotides Signup and view all the answers

Which of the following statements is incorrect regarding nucleic acids?

DNA and RNA have identical functions within a cell Signup and view all the answers

What is the primary structure of nucleic acids determined by?

The order of nitrogen bases Signup and view all the answers

How are the components of nucleic acids linked together?

By covalent bonds formed between nucleotides Signup and view all the answers

Which sugar component is present in RNA?

Ribose Signup and view all the answers

What is the primary function of mRNA in protein synthesis?

To carry instructions from DNA to the ribosome Signup and view all the answers

What type of bond connects nucleotides in a polynucleotide chain?

Phosphodiester bonds Signup and view all the answers

Which of the following correctly describes the structure of the DNA double helix?

Two strands of nucleotides twisted around each other Signup and view all the answers

In the context of nucleic acids, what does a nucleoside consist of?

A sugar and a nitrogen base Signup and view all the answers

Which of the following statements is true about the structure of a single strand of DNA?

It has a free phosphate group on the 5’ end Signup and view all the answers

Which pair of nucleotides correctly forms hydrogen bonds in DNA?

Adenine and Thymine Signup and view all the answers

Which class of bases includes adenine and guanine?

Purines Signup and view all the answers

What functional group on the sugar component interacts with the phosphate group in adjacent nucleotides?

Hydroxyl group on C3’ Signup and view all the answers

How many total bases are there in DNA and RNA combined?

Five Signup and view all the answers

What does a higher melting temperature (Tm) of DNA indicate?

Higher G-C content Signup and view all the answers

Which of the following can denature double helical DNA?

Disruption of base stacking Signup and view all the answers

How many codons are responsible for coding different amino acids?

61 Signup and view all the answers

What type of sugar is found in RNA molecules?

Ribose Signup and view all the answers

Which function does mRNA primarily serve in the cell?

Carrying genetic information for protein synthesis Signup and view all the answers

Which of these is NOT a type of RNA?

dRNA Signup and view all the answers

What is the primary structural composition of ribosomes?

65% RNA and 35% protein Signup and view all the answers

What role does transcription play in protein synthesis?

Copies DNA to mRNA Signup and view all the answers

What is the main function of tRNA in protein synthesis?

It transfers amino acids to the ribosome. Signup and view all the answers

Which of the following bases are classified as purines?

Adenine and Guanine Signup and view all the answers

What stabilizes the double helix structure of DNA?

Base-pairing, hydrophobic/hydrophilic interactions, and base stacking Signup and view all the answers

In which direction is the DNA sequence read during transcription?

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

What role do phosphodiester linkages play in nucleic acids?

They join nucleotides together to form nucleic acids. Signup and view all the answers

Study Notes

Nucleic Acids

Nucleic acids are organic molecules found in living organisms, primarily composed of Carbon, Hydrogen, Oxygen, and Nitrogen.
Four major classes of biomolecules are lipids, proteins, carbohydrates, and nucleic acids.
Nucleic acids are long biopolymers with structural similarities, serving as carriers of information, but with individual roles.
DNA (Deoxyribonucleic Acid) and RNA (Ribonucleic Acid) are types of nucleic acids.

Learning Outcomes

Understand the basic structure of a nucleotide.
Outline the structure of the DNA double helix.
Explain the structure and function of mRNA and tRNA for protein synthesis.
Appreciate the role of the ribosome for protein translation.

Questions

Students should use the provided TEAM platform for questions.
Students should not consider questions silly.
Emailed questions will be posted on the platform for the whole class to benefit from the answers.
Anyone with the answer to a question can contribute, fostering collaborative learning.

Biomolecules

A nucleoside consists of a base bonded to a sugar.
A nucleotide combines a nucleoside with a phosphate group.

The Central Dogma

DNA replicates to produce more DNA.
DNA is transcribed into RNA (mRNA).
mRNA undergoes translation into protein.

Nucleic Acids (Detailed)

DNA is deoxyribonucleic acid.
RNA is ribonucleic acid.
Both are long biopolymers with structural similarities.
Both carry information, but have individual roles.

Nucleic Acids as Polymers

Nucleic acids are polymers formed from monomers called nucleotides.
Nucleotides are composed of a nitrogenous base, a pentose sugar, and a phosphate group.

Nucleotide Structure

Nucleotides contain a nitrogenous base, a pentose sugar (ribose or deoxyribose), and a phosphate group.

Sugar: Pentose-Ribose

A five-carbon sugar, ribose, forms part of RNA's structure.

Sugar: RNA or DNA

RNA uses ribose.
DNA uses deoxyribose, differing by the presence of an oxygen atom on carbon 2.

Nitrogen Bases

There are five nitrogenous bases in DNA and RNA.
Two classes include pyrimidines and purines.

Bases: Purines

Adenine (A) and Guanine (G) are purines, larger, double-ringed structures.

Bases: Pyrimidines

Cytosine (C), Uracil (U), and Thymine (T) are pyrimidines (smaller, single-ringed structures).
Uracil (U) is found in RNA; thymine (T) is in DNA.

Nucleosides and Nucleotides

A nucleoside is a base bound to a sugar.
A nucleotide is a nucleoside attached to a phosphate group on the 5' carbon.

Names of Nucleosides and Nucleotides

Nucleosides and nucleotides have specific names based on the nitrogenous base (e.g., adenosine, cytidine).
Nucleotides often have "5'-monophosphate" added to their names (e.g., adenosine 5'-monophosphate).
Different names for DNA and RNA nucleosides/nucleotides reflecting the sugar (deoxy- prefix for DNA).

Bases

The order of nitrogenous bases (A, T/U, C, G) dictates the genetic code.

DNA Structure

DNA has a phosphate group at the 5' end and a hydroxyl group at the 3' end.
DNA sequences are read from the 5' end.
RNA, in contrast, has uracil (U) instead of thymine (T) and a ribose sugar instead of deoxyribose.

The DNA Double Helix

DNA exists as a double helix.
Two strands wind around each other, held together by hydrogen bonds between bases (A-T, C-G).
The phosphate-sugar backbone is on the outside of the helix, with the bases inside.

Base-Pairing

Hydrogen bonding between bases (A-T, G-C) holds the DNA strands together within the double helix.
Purines pair with pyrimidines for proper base pairing.

Base Pairing in the DNA Double Helix

Strands run antiparallel (3' to 5' and 5' to 3').
Strands are described as complementary.
Genetic information resides on one coded strand.
Another strand acts as an anti-template.

Helix Dimensions

Base pairs are 0.34 nm apart.
A complete turn of the helix is 3.4 nm.
Ten base pairs are found per turn.
External diameter of the helix is 2 nm.

Grooves

DNA has two grooves, major and minor, created by the twisting helix.
Proteins interact with specific sites exposed in these grooves (e.g., transcription factors, repressors, and silencers).

DNA Denaturation

DNA double strands can be separated by breaking hydrogen bonds (using changes in pH or heat).
Phosphodiester bonds are not broken during denaturation.
Temperature of melting (Tm) describes the temperature where 50% of the DNA becomes single-stranded.
Higher Tm signifies a greater proportion of G-C base pairs, requiring more energy to break.

Double Helical DNA Denaturation

DNA strands can be reversibly separated by extreme heat (above 80°C), changes in pH, and breaking hydrogen bonds.
This process does not affect phosphodiester bonds.
Renaturation restores the double helix.

The Genetic Code

64 codons, 61 for specific amino acids, and 3 for stop codons, describe the genetic code.
There is redundancy since multiple codons can code for the same amino acid.

Codon Usage Bias

Different organisms show variations in codon usage, favoring certain codons for specific amino acids.

RNA Synthesis & Function

Synthesis of mRNA occurs in the nucleus from a DNA template.
mRNA then translocates to the cytoplasm via nuclear pores for protein synthesis.

RNA Structure

RNA is a single-stranded polymer of nucleotides.
RNA employs ribose sugar and has bases A, G, C, and U.

Types of RNA

Ribosomal RNA (rRNA) is largely involved in ribosome structure.
Messenger RNA (mRNA) carries genetic information to direct protein synthesis.
Transfer RNA (tRNA) delivers amino acids to the ribosome during translation.

RNA Messenger - mRNA

mRNA is a copy of a DNA sequence (transcription).
mRNA carries genetic information needed for protein synthesis.
mRNA undergoes post-transcriptional modification.
mRNA leaves the nucleus and travels to the cytoplasm, where proteins are produced.
mRNA is a complementary copy of one DNA strand.

Ribosomal RNA - rRNA

Ribosomes, where proteins are synthesized, are found in the cytoplasm.
Ribosomes are composed primarily of rRNA (65%) and proteins (35%).
They participate in binding mRNA, essential for proper protein translation.

Transfer RNA - tRNA

tRNA transports amino acids to ribosomes during protein translation.
Many types of tRNA exist, one for each amino acid.
Each tRNA has an anticodon that complements an mRNA codon.

Protein Translation

Protein synthesis occurs at ribosomes in the cytoplasm.
mRNA, tRNA, and ribosomes collaborate for protein building, assembling amino acids as dictated by mRNA codons.

DNA Structure Review

A single strand of DNA has a free phosphate group at the 5' end and a free hydroxyl group at the 3' end.
The sequence moves from 5' to 3' ends, with bases indicating particular amino acid instructions.

Summary (Nucleic Acids)

Nucleotides consist of a nitrogenous base, a pentose sugar, and a phosphate group.
DNA and RNA have specific structures and functions related to encoding and translating genetic information.
RNA and DNA have complementary sequences.

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Description

Explore the fundamental concepts of DNA and RNA structure through this quiz. You'll learn about the role of grooves, the double helix arrangement, and the differences between nucleic acids. Test your knowledge on nucleotides, ribosomes, and more in molecular biology.