Nucleic Acids and Their Functions

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Questions and Answers

What do nucleic acids primarily function as in living organisms?

Repositories and functional expression of biological information (correct)

Energy reserves for cellular metabolism

Transport molecules for nutrients

Structural components of the cell membrane

Which of the following is NOT a known function of DNA?

Catalyzing chemical reactions (correct)

Transmission of information to the next generation

Storage of biological information

Serving as a template for RNA synthesis

What role do nucleoside triphosphates play in cellular metabolism?

They are responsible for transporting oxygen in the blood

They serve as an energy currency and regulatory signals (correct)

They act as genetic material in viruses

They are structural components of membranes

Which statement about monomeric subunits in nucleic acids is true?

Their specific sequences provide information essential for life Signup and view all the answers

Which type of RNA acts as an adapter to translate information from mRNA into amino acids?

Transfer RNA (tRNA) Signup and view all the answers

What role do nucleotides NOT play in cellular metabolism?

Regulatory enzymes for metabolic pathways Signup and view all the answers

Which sugar is found in RNA nucleotides?

Ribose Signup and view all the answers

What distinguishes deoxyribose from ribose in nucleotides?

Absence of one oxygen atom Signup and view all the answers

Which of the following statements about ribose and deoxyribose is false?

Both sugars are classified as hexoses. Signup and view all the answers

What is the basic structure of a nucleotide?

A sugar bound to a phosphate group and a nitrogenous base Signup and view all the answers

What is the structural characteristic of purines?

They consist of fused five- and six-membered rings. Signup and view all the answers

Which nitrogenous base in RNA replaces thymine found in DNA?

Uracil Signup and view all the answers

What links a nitrogenous base to the sugar in nucleosides?

N-glycosidic linkage Signup and view all the answers

Which of the following nucleobases is classified as a pyrimidine?

Thymine Signup and view all the answers

How does the structure of nucleotides differ from nucleosides?

Nucleotides include a phosphate group. Signup and view all the answers

Study Notes

Biomolecules

Biomolecules are large molecules essential for life
Types of biomolecules: proteins, carbohydrates, lipids, nucleic acids
Nucleic acids are polymers comprised of repeating units called nucleotides

Nucleic Acids and Nucleotides

Nucleic acids store and express genetic information
There are two types of nucleic acids: DNA and RNA
Nucleic acids are biopolymers made of monomers called nucleotides
Nucleotides consist of a sugar, a phosphate group, and a nitrogenous base
The types of sugars found in nucleotides are ribose and deoxyribose
Specific nitrogenous bases—adenine (A), guanine (G), cytosine (C), thymine (T), and uracil (U)—are fundamental components of DNA and RNA

Functions of DNA and RNA

DNA stores and transmits biological information
Genes are segments of DNA specifying protein or RNA production
Several RNA classes exist (rRNA, tRNA, mRNA):
- rRNA are ribosome components
- mRNA translates DNA code to proteins
- tRNA acts as an adaptor carrying amino acids to ribosomes

Nucleotides

Nucleotides have various roles in cellular metabolism:
- Energy currency (e.g., ATP)
- Involved in cellular communication
- Structural components of enzymes and cofactors.
Nucleotides are also constituents of nucleic acids (DNA and RNA)

Nucleotides – Basic Structure

Each nucleotide comprises a sugar bound to a phosphate group and a nitrogenous base

Nucleotides – Chemical Structure

Each nucleotide includes a phosphate group, a sugar, and a nitrogenous base

Nucleotides - (1) Sugar Base

Nucleotides have two types of sugars – ribose and deoxyribose
- DNA nucleotides only contain deoxyribose; RNA nucleotides only contain ribose.
Numbers on the sugar ring are "primed" to distinguish them from the numbered atoms of the nitrogenous bases

Ribose and Deoxyribose

Ribose and deoxyribose are five-carbon sugars
The only difference is that deoxyribose lacks the oxygen atom at the 2nd carbon position, which makes deoxyribose more stable.

Conformation of Ribose

Ribose has aldehyde and ring forms
RNA: β-D-ribofuranose ring form
DNA: β-2'-deoxy-D-ribofuranose exclusively

Nucleotides – (2) Phosphate Group

Nucleotides are polar due to highly ionized oxygen atoms in the phosphate groups
ATP (adenosine triphosphate) is a crucial nucleotide in energy transfer in cells.

Nucleotides – (3) Nitrogenous Bases

Nitrogenous bases are organic molecules with nitrogen and act as bases in chemical reactions.
Planar, aromatic, and heterocyclic structures
Derived from purines (adenine & guanine) or pyrimidines (cytosine, thymine & uracil)

Two Classes of Nitrogen Bases

Purines (A, G) are double-ring structures
Pyrimidines (C, T, U) are single-ring structures

Purines and Pyrimidines

Purines include adenine and guanine.
Pyrimidines include cytosine, thymine, and uracil.

Nucleoside

Nucleoside formed by removing the phosphate group from a nucleotide

Structure – Review

Nucleotides are the building block of nucleic acids

Bonding of the groups to the sugar – (1) Nitrogenous Base

The nitrogenous base is connected to the sugar via an N-glycosidic bond, which is a covalent bond.
Purines (A, G) bond at the C1' carbon via the N9 atom
Pyrimidines (C, T, U) bond at the C1' carbon via the N1 atom

Bonding of the groups to the sugar – (2) Phosphate Group

The phosphate group is esterified to the 5' carbon of the sugar

To Review at home

The base, sugar and phosphate are joined covalently in a nucleotide
The elements of water are removed to form an N-glycosidic bond.
- A hydroxyl group from the pentose sugar
- A hydrogen from the nitrogenous base

Nucleotides (Summary)

Monomers of nucleic acids (DNA, RNA)
Nucleotides link to create nucleic acids via esterification

Naming Conventions

Nucleosides end in "-sine" (purines) or "-dine" (pyrimidines)
Nucleotides add "mono-," "di-," or "triphosphate" to the nucleoside name

Nomenclature of Nucleosides and Nucleotides

Nucleotides vary by the bases and sugars they contain; their names often reflect this variation.
These terms are important in biochemistry for naming and describing nucleotides

DNA

DNA is the repository of genetic information
DNA is found in chromosomes—the structures in which genetic material is organized
In eukaryotic cells, DNA is packaged around proteins called histones to form nucleosomes
Bacteria lack a membrane-bound nucleus and thus DNA is found in the nucleoid region.

Structure of DNA

DNA is a polymer of deoxyribonucleoside monophosphates linked through phosphodiester bonds.
DNA exists as a double-stranded helix
- The two strands wind around the central axis

Phosphodiester Bonds

Phosphodiester bonds are the covalent bonds connecting nucleotides in a DNA strand or RNA strand—forming the “backbone” of the nucleic acid

Formation of the Phophosdiester Bonds

The bonds form between the 3' hydroxyl group of one nucleotide and the 5' hydroxyl group of an adjacent nucleotide, releasing water.

DNA Structure/Conformation

Complementary base-pairing (A-T, G-C) stabilizes the DNA double helix and is crucial for DNA replication.
Antiparallel arrangement of strands in DNA
Base stacking—hydrophobic interactions between bases

Watson-Crick Model

Offset pairing of the two DNA strands; The two strands wind around an axis to form the double helix structure
There are major and minor grooves within the helix,
The double helix is stabilised by:
- Metal cations shielding backbone charges.
- Base stacking.
- Van der Waals interactions

Double Helix

The two strands in the DNA helix are antiparallel, winding around a central axis
The grooves in the DNA helix provide access for regulatory proteins.

Base Pairing

Specific pairing of nitrogenous bases (A with T and G with C).

Bonding of Base Pairs

The base pairs are held together by hydrogen bonds

Separation of the Two DNA Strands

DNA strands separate when the hydrogen bonds between bases are disrupted; this can occur by altering pH or heating the solution
Separation occurs at a temperature called the melting temperature (Tm).

Replication of DNA

DNA replication involves separation of parent strands with each strand acting as a template

DNA Interaction with Proteins

DNA interacts with proteins to form a complex structure, called chromatin, or chromosomes
These proteins tightly package DNA to fit into the cell nucleus, ensuring that it is protected and controlled properly.

Histones and the Formation of Nucleosomes

Histones are proteins with positive charges that bind tightly to negatively charged DNA, organizing it into condensed structures
DNA wraps around histone octamer protein clusters, forming nucleosomes

Histones (Summary)

Specific types of positively charged proteins
Play a critical role in DNA organization.
Binding to DNA causes DNA to coil into a compacted structure

Structure of RNA

RNA is a single-stranded polymer of ribonucleotides linked through phosphodiester bonds

Types of RNA

Three major types in protein synthesis—rRNA, tRNA, mRNA
- rRNA : structural components of ribosomes (protein synthesis machines)
- tRNA: adaptor molecules carrying amino acids to the ribosome
- mRNA: carries the genetic code from the DNA to the ribosome

Messenger RNA (mRNA)

mRNA carries the genetic instructions from DNA to direct protein synthesis
mRNA comprises a polypeptide sequence specifying for a certain protein.

mRNA Structural Characteristics

mRNA contains a 5’ cap, a coding region, and a poly-A tail
- These special features help stabilize and translate the mRNA strand into a protein.
Eukaryotic mRNA structure is unique and allows for efficient protein production.

Ribosomal RNA (rRNA)

rRNAs are essential components of ribosomes
rRNAs make up a large portion of the cell's total RNA

Transfer RNA (tRNA)

tRNAs act as carriers for amino acids
They use a specific structure (secondary and tertiary) and unique bases to accurately transport amino acids during protein synthesis

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Description

Test your knowledge on the primary functions of nucleic acids, the roles of DNA and RNA, and the structure of nucleotides. This quiz covers essential concepts related to nucleic acids and their importance in cellular metabolism and protein synthesis.