Molecular Biology: DNA Function and Replication

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Questions and Answers

What is the primary function of DNA within a cell?

Protein synthesis

Energy production

Storage and transfer of genetic information (correct)

Cellular respiration

Where is most of the DNA located in a cell?

In the cytoplasm

Within the cell nucleus (correct)

In ribosomes

In the mitochondria

Which sugar is found in RNA?

2′-deoxyribose

Glucose

Fructose

Ribose (correct)

What component is NOT part of a nucleotide?

Amino acid Signup and view all the answers

What distinguishes 2′-deoxyribose from ribose?

Missing an oxygen at carbon 2′ Signup and view all the answers

What type of acids do nucleotides combine to form?

Nucleic acids Signup and view all the answers

Which of the following bases is derived from pyrimidine?

Thiamine (vit B) Signup and view all the answers

What does the prefix 'deoxy-' in 2′-deoxyribose indicate?

Missing an oxygen Signup and view all the answers

What term describes the type of DNA replication where one strand is the parent and the other is newly synthesized?

Semiconservative replication Signup and view all the answers

What is the role of DNA helicase during DNA replication?

To unwind the DNA double helix Signup and view all the answers

During DNA replication, which strand is synthesized continuously?

Leading strand Signup and view all the answers

What is the purpose of the enzyme primase in DNA replication?

To generate RNA primers for DNA synthesis Signup and view all the answers

What occurs during the termination step of DNA replication?

RNA primers are removed and replaced with DNA Signup and view all the answers

In the Meselson-Stahl experiment, what determined the observation of heavy and light DNA strands?

Growth in a nitrogen isotope medium Signup and view all the answers

What characteristic distinguishes Okazaki fragments during DNA replication?

They consist of multiple RNA primers Signup and view all the answers

What is the primary role of hydrophobic interactions in cell membranes?

To provide structural stability Signup and view all the answers

What is the genetic information carried in eukaryotic chromosomes called?

Genome Signup and view all the answers

Which of the following statements describes prokaryotic chromosomes?

They have a simple structure Signup and view all the answers

What structural component allows DNA to fit into the cell nucleus in eukaryotes?

Histone proteins Signup and view all the answers

How many pairs of chromosomes do humans have?

23 pairs Signup and view all the answers

What is the first level of structure in eukaryotic chromosomes?

Nucleosome Signup and view all the answers

How does the structure of eukaryotic chromosomes vary among different species?

By the size and number of chromosomes Signup and view all the answers

Which part of the chromosome provides structural support?

Histone Signup and view all the answers

What complex of DNA and protein forms the eukaryotic chromosomes?

Chromatin Signup and view all the answers

What type of proteins are represented by red beads in the chromosome structure description?

Histone proteins Signup and view all the answers

What is formed when a sugar, base, and phosphate combine?

A nucleotide Signup and view all the answers

Which part of a nucleotide chain is responsible for its directionality?

The free hydroxyl group and free phosphate group Signup and view all the answers

How is the sequence of bases in a nucleic acid strand conventionally read?

From the 5′ end to the 3′ end Signup and view all the answers

What type of linkage bonds sugar molecules in the nucleotide chain?

3′,5′-phosphodiester linkages Signup and view all the answers

What charge does each nonterminal phosphate group in the nucleic acid backbone carry?

1- charge Signup and view all the answers

What does the primary structure of a nucleic acid depend on?

The sequence of bases present Signup and view all the answers

What is the term used to describe a nucleotide derived from a nucleoside?

5′-monophosphate Signup and view all the answers

In the nucleotide structure, what is located at the 5′ end?

Free phosphate group Signup and view all the answers

What type of bond is formed between phosphate groups and sugar molecules in a nucleotide?

Phosphoester bonds Signup and view all the answers

What does the sequence 5′ T–G–C–A 3′ represent?

A nucleotide chain base sequence Signup and view all the answers

What is the primary difference between a nucleoside and a nucleotide?

A nucleotide includes a phosphate, but a nucleoside does not. Signup and view all the answers

Which of the following correctly describes how nucleotides are formed?

Nucleotides are formed from the reaction of a sugar and a base followed by a reaction with a phosphate. Signup and view all the answers

What type of bond connects the sugar to the nitrogenous base in a nucleoside?

A β-N-glycosidic bond Signup and view all the answers

Which suffix is used to name nucleosides derived from pyrimidine bases?

-idine Signup and view all the answers

What is produced during the formation of a nucleoside?

A molecule of water Signup and view all the answers

In the context of nucleotide formation, what position on the sugar does the phosphate group attach?

C5′ Signup and view all the answers

What indicates that a sugar molecule is deoxyribose in a nucleoside?

The presence of the prefix deoxy- Signup and view all the answers

What type of reaction occurs during the formation of nucleotides and nucleosides?

Condensation reaction Signup and view all the answers

Which attachment is specific to purine bases in nucleoside formation?

Attachment through N9 Signup and view all the answers

What is the solubility characteristic of nucleosides compared to free heterocyclic bases?

Nucleosides are more soluble because of the pentose’s -OH groups. Signup and view all the answers

Study Notes

Nucleic Acids

Nucleic acids are unbranched polymers made up of nucleotide monomer units
Two main types: Deoxyribonucleic acid (DNA) and Ribonucleic acid (RNA)

Types of Nucleic Acids

DNA: Found primarily in the cell nucleus. Its function is storing and transferring genetic information passed from existing cells to new cells during cell division.
RNA: Found in all parts of a cell. Functions primarily in the synthesis of proteins, which carry out essential cellular functions.

Components of Nucleic Acids

Sugar: A five-carbon (pentose) sugar.
Phosphate: Derived from phosphoric acid.
Nitrogenous bases: Four heterocyclic amines: Purines (Adenine, Guanine) and Pyrimidines (Cytosine, Thymine, Uracil)

Nucleotides

Nucleotides are the structural building blocks of nucleic acids.
Three subunits:
Pentose sugar (ribose or 2'-deoxyribose)
Nitrogenous base
Phosphate group(s)

Nucleotide Formation

Happens in two steps:

Sugar and base combine to form nucleoside.
Nucleoside combines with phosphate to form nucleotide.

A bond called ẞ-N-glycosidic linkage joins sugar to base.
A molecule of water is formed as by-product when the sugar and base (form nucleoside) and nucleoside and phosphate (form nucleotide) combine.
Nucleosides are named as derivatives of the base with a suffix (-idine for pyrimidines, -osine for purines). The prefix "deoxy" is added is sugar is deoxyribose. No prefix is used if ribose is present.

Nucleotide Formation: Phosphate

The phosphate component is derived from phosphoric acid (H3PO4).
Under cellular pH, phosphoric acid loses two hydrogen atoms to form a hydrogen phosphate ion.

Nucleotides: Structural Building Blocks for Nucleic Acids (continued)

Adenosine triphosphate (ATP), a ribonucleotide, is an important example.
It is the primary energy currency of the cell.
Different abbreviations are used to represent different types of nucleotides.

Nucleotides: Pentose Sugar

Sugar unit is either ribose or 2'-deoxyribose.
The difference between the two sugars is at carbon 2', where ribose has an -OH group, and 2'-deoxyribose has an -H atom.

Nucleotides: Nitrogen-Containing Heterocyclic Bases

Purines (Adenine and Guanine) are double-ring structures
Pyrimidines (Cytosine, Thymine, and Uracil) are single-ring structures.
To remember purines, use the mnemonic: "Pure As Gold"
Caffeine and thiamine (Vitamin B1) are derivatives, respectively, of purines and pyrimidines

DNA Structure: The Double Helix

DNA is a double helix
Two strands of DNA form a right-handed double helix
The bases in opposite strands hydrogen bond according to the AT/GC rule.
Two strands are antiparallel (orientated in opposite 5' to 3' directions)
There are ~10.0 nucleotides in each strand per complete 360° turn of the helix

DNA Structure: Base Pairing

Only A-T and C-G base pairs occur because of a physical restriction that is due to the size of the interior of the helix.
The base-pairing enables a double helix structure

DNA Structure: Hydrogen Bonding and Base Stacking

Hydrogen bonds between base pairs are important for stabilizing the DNA double helix.
Base-stacking interactions involving a given base and the parallel bases above and below it also stabilize the helix.
The bases are positioned with their planes parallel

DNA Structure: Chromosomes

Chromosomes are pieces of DNA in cells
Prokaryotes have one chromosome, and the structure is simple
Eukaryotes have multiple chromosomes each having multiple levels of structure
The first level is nucleosome: DNA wrapped around a small disk including histone proteins

DNA Replication

This biochemical process, which produces exact copies of DNA molecules, is critical for cells to perform correctly.
If mistakes are made during DNA replication in genes that are essential for the correct function of a cell, it can be lethal.

DNA Replication: Overview

Chromatin disassembly
DNA double helix unwinding
Primer binding
Elongation
Termination

Telomeres

Telomeres function as protective caps at the ends of linear DNA.
They protect important genes from being deleted as cells divide and DNA shortens during replication
A 6 base pair sequence (TTAGGG) is repeated 100-1000 times in humans.

Chromosomes (continued)

Chromosomes are a complex of DNA and protein
Typically, a chromosome is about 15% by mass DNA and 85% by mass protein.
Chromosomes occur in homologous pairs, which are similar but not identical, for example, blue eyes versus brown eyes.

Bacterial DNA Replication

DNA replication begins at a unique sequence called replication origin
Replication occurs bidirectionally at a high rate

Eukaryotic DNA Replication

DNA replication in eukaryotes is much more complex
The human genome consisting of billions of nucleotide pairs makes this process more complex
Replication begins at many origins and proceeds bidirectionally

Information Flow in Biological Systems

The central dogma of molecular biology states that the flow of genetic information in cells is one-way from DNA to RNA to protein.

Types of RNA

hnRNA: Heterogeneous nuclear RNA, is RNA formed directly by DNA transcription.
mRNA: Messenger RNA carries instructions for protein synthesis and the length varies with the length of protein synthesis.
snRNA: Small nuclear RNA facilitates the conversion of hnRNA into mRNA.
rRNA: Ribosomal RNA combines with proteins to form ribosomes, the sites of protein synthesis
tRNA: Transfer RNA, delivers amino acids to the sites for protein synthesis.

Alternative Splicing

Different proteins can be produced from a single gene
Important for the complexity of organisms such as humans where the number of proteins is high.

The Genetic Code

mRNA is a sequence of amino acids in the mRNA that determines the amino acid order of the protein
A given triplet in mRNA will translate to a specific amino acid. The triplet is called a codon.
A total of 64 possible codon combinations, and certain codons signal the start and end of polypeptide chain.
The three codons (UGA, UAA, and UAG) are stop signals for protein synthesis.
AUG is the start codon that codes for methionine.

Translation: Protein Synthesis

The process is carried out on ribosomes, which are complexes of ribosomal RNA and proteins.
Translation starts from a start codon on mRNA
The tRNA molecule (with attached amino acid) recognizes the codon
The first tRNA leaves and the next tRNA arrives to bond to mRNA, continuing the chain until a stop codon is reached, and the polypeptide chain is released.

Post-Translation Processing

Proteins undergo modifications after translation to take their final form. These processes include: removal of met, formation of disulfide bridges, and completion of protein folding.

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Description

Test your knowledge on the fundamental functions of DNA within a cell, as well as the various components involved in DNA replication. This quiz covers essential concepts such as nucleotide structure, types of DNA replication, and key experiments in molecular biology. Perfect for students studying cell biology or genetics.