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11.3: Metabolism and Replication

Difficulty Level: Basic Created by: CK-12
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What is an RNA world?

DNA passes most genetic information today. But some scientists think that for the first life on Earth genetic information was passed by RNA. They call this the RNA world hypothesis.


Organic molecules must carry out the chemical work of cells. This is their metabolism. Living organisms need chemical reactions to live, grow, and reproduce. The chemical reactions occur in sequences of steps. These sequences are known as metabolic pathways. The metabolic pathways are very similar for all life on Earth. That includes single celled bacteria that have been around for billions of years. It includes the most complex life forms on Earth today. What does it mean that the metabolic pathways are so similar for all life? This means that the metabolic pathways evolved very early in Earth's history.


Living cells need organic molecules, known as nucleic acids. Nucleic acids are molecules store genetic information. They pass that genetic information to the next generation. Deoxyribonucleic acid (DNA) is the nucleic acid that carries information for nearly all living cells today. DNA has done this for most of Earth's history. Ribonucleic acid (RNA) delivers genetic instructions to the location in a cell where protein is synthesized. RNA regulates protein synthesis. Some scientists think that RNA was the first replicating molecule.

The famous double helix structure of DNA is seen in this animation: http://upload.wikimedia.org/wikipedia/commons/8/81/ADN_animation.gif.

A segment of DNA that is inheritable is a gene. Every organism has a collection of genes that code for the traits that organism could have. Not all genes are expressed so knowing all of your genes does not tell you exactly who you are.


  • gene: A piece of DNA that passes genetic information from parent to offspring.
  • metabolism: The chemical work of cells. The chemical reactions a living organism needs to live, grow and reproduce.
  • nucleic acid: Biological molecules necessary for life; includes DNA and RNA


  • An organism's metabolism is the chemical reactions that allow it to live, grow, and reproduce.
  • Nucleic acids pass genetic information to the next generation.
  • DNA passes genetic information for living cells. RNA passes genetic information for protein synthesis.


Use this resource to answer the questions that follow.


  1. What is the function of the nucleus?
  2. What is DNA?
  3. What are genes?
  4. What do genes do?
  5. What is a chromosome?


  1. What is the purpose of an organism's metabolism?
  2. Metabolic pathways are similar between very simple and very complex organisms. What do scientists think this means?
  3. What do nucleic acids do? What are the two nucleic acids?




Piece of DNA that passes genetic information from parent to offspring.


Chemical work of cells; the chemical reactions a living organism needs to live, grow, and reproduce.
nucleic acid

nucleic acid

Biological molecules necessary for life; includes DNA and RNA

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Difficulty Level:
6 , 7
Date Created:
Jan 04, 2013
Last Modified:
Mar 23, 2016
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