Question

How many chromosomes does a human cell have? What are these chromosomes made of? (pp. 50–51)

Short answer

Answer: Human cells have 46 chromosomes, arranged in 23 pairs. These chromosomes are made up of DNA and proteins, with the DNA carrying the genetic information needed for an organism's growth, development, and function.

Step-by-step solution

Determine the number of chromosomes in a human cell

The number of chromosomes in a human cell is 46. These chromosomes exist as 23 pairs, with one chromosome coming from each parent.

Describe the structure of chromosomes

Chromosomes are made up of a complex combination of DNA (deoxyribonucleic acid) and proteins. DNA contains genetic information that controls the traits, development, and functioning of every living organism, while proteins help maintain the structure of the chromosome and regulate gene activity.

Understanding the role of genes

Genes are segments of DNA that code for specific functional units, such as proteins or RNA molecules. They contain instructions needed to build and maintain an organism's cells and pass traits from parents to offspring. Each chromosome carries several genes, and the human genome contains approximately 20,000 to 25,000 protein-coding genes. In summary, human cells have 46 chromosomes, arranged in 23 pairs. These chromosomes are made up of DNA and proteins, with the DNA carrying the genes that encode the information needed for an organism's growth, development, and function.

Key concepts

DNA structure

DNA, or deoxyribonucleic acid, is the molecule that forms the foundation of genetic information in living organisms. At the core of DNA structure is a double helix, which looks like a twisted ladder. Each "rung" of this ladder is made up of pairs of nucleotides. There are four different nucleotide bases in DNA: adenine (A), thymine (T), cytosine (C), and guanine (G).

A pairs with T, and C pairs with G. This pairing is known as complementary base pairing. These base pairs are held together by hydrogen bonds.

• The order (or sequence) of these bases forms the genetic instructions needed to build proteins.
• The backbone of the DNA strand is formed by sugar and phosphate molecules.

Proteins, in combination with DNA, form a structural entity known as chromatin. Chromatin further coils and compacts to form chromosomes, ensuring that vast amounts of DNA fit inside a cell's nucleus.

gene function

Genes are specific segments of DNA that carry the instructions for building proteins, which are essential for various biological functions. A gene's primary function is to dictate how a protein is constructed, determining its amino acid sequence.

Proteins resulting from gene expression play critical roles, such as:

• Acting as enzymes to speed up chemical reactions in the body.
• Providing structure to cells and tissues.
• Sending signals and coordinating bodily functions.

Genes also influence traits, such as eye color or height. Variations or mutations in genes can lead to differences in these traits or contribute to certain diseases. Understanding how genes function is crucial for advances in medicine and biology, as it can lead to improved treatments and preventive measures.

human genome

The human genome is the complete set of genetic information for humans. It includes all of the DNA contained in a cell. With approximately 3 billion DNA base pairs, the genome serves as a comprehensive instruction manual for the growth, development, and functioning of human beings.

Important aspects of the human genome include:

• It contains about 20,000 to 25,000 protein-coding genes.
• These genes are spread across 23 pairs of chromosomes.
• The genome encodes all the proteins our bodies need to operate effectively.

It's important to note that only a small percentage of the genome actually codes for proteins. The rest includes non-coding DNA, which plays roles in regulating gene expression and maintaining chromosome structure. The mapping and understanding of the human genome, as highlighted by the Human Genome Project, have provided valuable insights into human biology and disease.

chromosomal pairs

Human cells contain a total of 46 chromosomes, organized into 23 pairs. Each pair consists of one chromosome inherited from the mother and one from the father. This combination ensures genetic diversity in offspring, as each child receives a unique mix of parental genes.

Key points about chromosomal pairs include:

• The first 22 pairs are called autosomes and are identical in both males and females.
• The 23rd pair is known as the sex chromosomes, which determine an individual’s sex - typically XX for females and XY for males.

Each chromosome in a pair is similar in structure but may contain variations in the alleles of some genes, contributing to differences in traits between individuals. These pairs are crucial for normal cellular function as they ensure the right amount of genetic material is present and accurately replicated during cell division. Understanding chromosomal pairs is fundamental in genetics, as abnormalities in these can lead to various genetic disorders.