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# 4.4: RNA

Difficulty Level: At Grade Created by: CK-12
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How does the information move from the nucleus, where the DNA is located, to the cytoplasm, where the ribosomes are?

RNA, the other nucleic acid, that's how. Specifically mRNA. RNA, the middle player in the central dogma. This image is an abstract representation of tRNA. Without tRNA, mRNA, and rRNA, proteins cannot be made.

### RNA

DNA alone cannot “tell” your cells how to make proteins. It needs the help of RNA , ribonucleic acid, the other main player in the central dogma of molecular biology. Remember, DNA "lives" in the nucleus, but proteins are made on the ribosomes in the cytoplasm. How does the genetic information get from the nucleus to the cytoplasm? RNA is the answer.

#### RNA vs. DNA

RNA, like DNA, is a nucleic acid. However, RNA differs from DNA in several ways. In addition to being smaller than DNA, RNA also

• consists of one nucleotide chain instead of two,
• contains the nitrogen base uracil (U) instead of thymine,
• contains the sugar ribose instead of deoxyribose.

#### Types of RNA

There are three main types of RNA, all of which are involved in making proteins.

1. Messenger RNA (mRNA) copies the genetic instructions from DNA in the nucleus, and carries the instructions to the cytoplasm.
2. Ribosomal RNA (rRNA) helps form ribosomes, the organelle where proteins are assembled.
3. Transfer RNA (tRNA) brings amino acids to ribosomes, where they are joined together to form proteins.

Shown are the three types of RNA and their roles: (1) mRNA contains the genetic message, (2) tRNA transfers the amino acids to the ribosome, (3) rRNA is the main component of the ribosome. More on the roles of the RNAs will be discussed in these concepts: "Transcription of DNA to RNA," "Genetic Code," and "Translation of RNA to Protein."

### Summary

• RNA differs from DNA in several ways.
• There are three main types of RNA: messenger RNA (mRNA), ribosomal RNA (rRNA), and transfer RNA (tRNA).
• Each type plays a different in role in making proteins.

### Practice I

Use this resource to answer the questions that follow.

• http://www.hippocampus.org/Biology $\rightarrow$ Biology for AP* $\rightarrow$ Search: RNA Structure and Function
1. List three structural differences between DNA and RNA.
2. What is the function of mRNA?

### Review

1. What are the three main types of RNA? Describe their roles.
2. Compare and contrast DNA and RNA.

## Date Created:

Feb 24, 2012

Aug 25, 2014
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