Question

In cells, most RNA molecules are ________ and DNA molecules are ________. a. single-stranded; double-stranded b. double-stranded; single-stranded c. double-stranded; double stranded

Short answer

a. single-stranded; double-stranded

Step-by-step solution

Identify RNA Structure

RNA molecules are typically single-stranded in cells, although they can form complex three-dimensional shapes by folding upon themselves through base pairing.

Identify DNA Structure

In cells, DNA is primarily found as a double-stranded helix, where two complementary strands are joined together by hydrogen bonds between base pairs.

Match the Structures to the Options

Based on the identified structures: RNA is single-stranded and DNA is double-stranded. Therefore, we need to select option 'a' which states that RNA molecules are single-stranded and DNA molecules are double-stranded.

Key concepts

RNA Structure

RNA, which stands for ribonucleic acid, is a crucial biomolecule in the world of molecular biology. Unlike DNA, RNA is primarily single-stranded in cells. This single-stranded nature gives RNA its flexibility to fold into various structures, enabling it to perform an array of functions within the cell. Although it's single-stranded, RNA can still form complex three-dimensional shapes through intra-molecular base pairing. This happens when complimentary sections within the same molecule pair up, much like how pieces of a puzzle fit together.

RNA plays multiple roles in cells:

• Messenger RNA (mRNA) carries genetic information from DNA to the ribosome, where proteins are synthesized.
• Transfer RNA (tRNA) helps in the decoding of mRNA into proteins.
• Ribosomal RNA (rRNA) is a key component of the ribosome's structure and function.

The versatility of RNA highlights its importance beyond just being a genetic messenger. Recent discoveries have shown that RNA can also act as an enzyme, a regulatory molecule, and more.

DNA Structure

DNA, or deoxyribonucleic acid, is the hereditary material in humans and almost all other organisms. In cells, DNA typically exists as a double-stranded helix. This means that two long strands of nucleotides are wound around each other, resembling a twisted ladder. Each rung of this ladder consists of a pair of nitrogenous bases connected through hydrogen bonding.

The four bases in DNA are adenine (A), thymine (T), cytosine (C), and guanine (G). Base pairing rules are specific:

• Adenine always pairs with thymine.
• Cytosine pairs with guanine.

These specific pairings allow the DNA to replicate with high fidelity, ensuring genetic information is accurately passed on during cell division. DNA's double-stranded nature provides durability and stability, which is essential for storing genetic instructions over generations. Furthermore, the structure allows for easy access for transcription, where segments of DNA are copied into RNA.

Molecular Biology

Molecular biology is a branch of science that delves into the molecular fundamentals of biological processes. It primarily focuses on understanding how various molecules within a cell interact and function. A central theme of molecular biology is the flow of genetic information, often referred to as the "Central Dogma." This refers to the process by which DNA is transcribed into RNA, which is then translated into proteins, the workhorses of the cell.

The study of molecular biology includes several key aspects:

• DNA Replication - the process by which DNA makes a copy of itself during cell division.
• Transcription - where DNA is transcribed to RNA. This is a crucial step, as RNA acts as an intermediary, carrying the genetic blueprint to produce proteins.
• Translation - where the RNA is used to synthesize proteins, which perform most cellular functions.

Advancements in molecular biology have propelled our understanding of genetics and heredity, allowing for developments in biotechnology, medicine, and genetics. This field provides foundational knowledge for tackling biological mysteries, from genetic disorders to improving crop yields.