The Building Blocks of Life

nuclear family

A family welcomes its newest member.

© Ariel Skelley—Digital Vision/Getty Images

 

Introduction

Have you ever been told that you have your mother's eyes? Or maybe your father's hair? Or your grandmother's chin? What do you think people mean when they say something like that?

Think of characteristics of your mother, father, or any family member that you share with them. 

In your science journal, answer the following questions.

1.  What are some similar traits that you have with a family member?

2.  What are some different traits that you have with a family member?

3.  What do you mean when people say you look like your father or mother?

 

Deoxyribonucleic Acid (DNA)

Deoxyribonucleic acid, or DNA, is a tiny molecule that is the blueprint for all life. To make the complex organism  YOU, you got half of your DNA instructions from your mother and a half from your father. 

 

All living things, including things that were once living, contain DNA. Everything from microscopic bacteria to towering trees, huge blue whales, and small insects contain DNA. Even woolly mammoth fossils still contain DNA that we can study now, thousands of years after they died!

Proteins help form cells; each cell stores an organism's DNA within its nucleus. Complex living organisms can cram so much information, or genetic material, inside every cell.

In your science journal, answer the following questions.

1.  What comes to your mind when you hear the word "DNA?"

2.  What comes to your mind when you hear the word "protein?"

 

Let's explore how DNA is contained in a cell with a nucleus called a eukaryotic cell by looking at the image below.

The image above shows the genetic parts of the eukaryotic cell.

 

        Eukaryotic Cell

Eukaryotic cells are found in almost all living organisms. They hold genetic material, or DNA, within the nucleus. 

Eukaryotic Cell

 

        Chromosomes

Genes are tightly packed into pairs of structures called chromosomes. The job of chromosomes is to help keep the DNA within each cell. The structure of chromosomes keeps DNA wrapped tightly around a protein called histone.

This complete instruction book of genes, or genome, for a human, contains 23 pairs of chromosomes, for a total of 46.

Twenty-two of these pairs looks the same in both males and females. However, the 23rd pair—the sex chromosomes—is different. Females have two copies of the X chromosome, while males have one X chromosome and one Y chromosome.

A human embryo gets 23 chromosomes from its mother and 23 from its father. The genetic code is passed down from biological parents to offspring. Each chromosome has two identical strands, called chromatids, joined together.

Sometimes errors happen when chromosomes are passed down, and the offspring gets more or fewer chromosomes. This can affect how an individual looks and behaves. Down syndrome is one example of a chromosomal condition. Children born with Down syndrome have an extra copy of chromosome #21, creating a total of 47 chromosomes, and they often have delays in their development. 

In your science journal, answer the following questions.

1.  What is the job of chromosomes?

2.  How is the 23rd pair of chromosomes different for males and females?

 

        Genes

 

 

 

A gene is a basic unit of information made out of strands of DNA. It controls how offspring develop different traits from the mother and father. For example, one gene could dictate how your eyes look while another may decide how your face is shaped.

For example, one gene could dictate how your eyes look while another may dictate how your face is shaped.

Every person has two copies of each gene, one inherited from each biological parent. Different forms of a gene are called alleles, which is why each person looks unique. Different alleles, for instance, produce different hair colors, such as brown, blonde, red, and black. 

Gene Alleles

In your science journal, answer the following questions.

1.  What is a gene?

2.  Why does each person look unique?

 

        DNA

DNA is the hereditary material in humans and almost all other organisms. It contains the instructions for developing, growing, and reproducing. If all the DNA from one human cell were unraveled and put on end to end, it would be about six feet long.

DNA is made of four types of bases: adenine (A), cytosine (C), guanine (G), and thymine (T). These bases go together to form base pairs. The sequence of base pairs in each part of the DNA molecule is called a gene, and genes decide how organisms will develop.

Most DNA is in the nucleus of cells throughout an organism.

DNA has two important properties:

The double helix shape of the DNA molecule looks like a twisted ladder. Because of this shape, DNA can make exact copies of itself and pass biological instructions from old to new cells. The information stored in DNA is needed for building and maintaining all parts of an organism.

DNA

In your science journal, answer the following question.

1.  What are the two important properties of DNA?

 

        RNA

Ribonucleic acid, or RNA, is a single-stranded molecule that acts like a messenger to move genetic information stored in the DNA in a cell to other parts of the cell. RNA gives parts of the cell the blueprints for building proteins.

The structure of RNA is similar to that of DNA. But instead of having A, C, G, and T, RNA has A, C, G, and U. RNA has uracil (U) instead of thymine (T).

RNA molecules carry genetic information using the A, C, G, and U codes. RNA makes a copy of part of the DNA, and this strand of RNA has a unique code that parts of the cell can read to create different proteins. This process is called transcription. 

RNA

In your science journal, answer the following question.

1.  What are some differences between RNA and DNA?

 

        Nucleotides

The basic building block of DNA is called a nucleotide. Each nucleotide comprises six molecules: one sugar molecule, one phosphate molecule, and one of four bases (A=adenine, T=thymine, C=cytosine, and G=guanine). The order of nucleotide bases (A, T, G, and C) along the DNA strand is like a recipe that tells the organism how to develop itself, including all of its cells, tissues, and organs. This constitutes the genetic code.

Nucleotides

In your science journal, answer the following questions.

1.  What are four types of bases found in nucleotides?

2.  How is the order of these bases like a recipe?

 

        Amino Acids

Proteins are the most common substances in humans and other animals, and they are needed to build and repair cells and tissues. Amino acids form proteins. Different combinations of amino acids make up different proteins.

There are 20 types of amino acids, and they can be put into many different orders. For example, the protein pepsin is a chain of about 320 amino acids. Antibodies are made of different combinations of amino acids to fight different bacteria and viruses.

Humans can naturally make 10 of the 20 amino acids in their bodies. To get the other ten amino acids, people can eat foods with proteins that have these amino acids.

Amino Acids

In your science journal, answer the following question.

1.  What role do amino acids play in your body?

 

        Proteins

Proteins are necessary for most life on Earth. They can be thought of in two different ways—as nutrients (which you can get from food that contains protein) or as large molecules that do many jobs within an organism.

Proteins are made of amino acids. Amino acids can be formed into proteins inside cells, and they help carry out tasks under the direction of genes.

Without proteins, which do most of the work in our bodies, most organisms would not be able to function correctly. The body uses proteins to build and repair itself. Pepsin is a protein that helps your body digest and breaks down food. Antibodies are proteins your immune system uses to fight bacteria and viruses that can make you sick.

Proteins are the most common substances in humans and other animals and are even found in plants. Proteins in foods help the body build bones, muscles, skin, and blood. The body breaks down proteins found in animals or plants into amino acids, then reuses the amino acids to form different proteins

Proteins

In your science journal, answer the following questions.

1.  What do proteins do?

2.  What are some specific examples?

 

Let's Practice