U8L1 DNA Structure & Function

Unit 8 Lesson 1 DNA Structure and Function

Copyright © Houghton Mifflin Harcourt Publishing Company


Indiana Standards


• 8.3.4 Understand the relationship between deoxyribonucleic acid (DNA), genes, and chromosomes.

Cracking the Code


What is DNA?

• The genetic material in cells is contained in a molecule called deoxyribonucleic acid, or DNA.

• Scientists describe DNA as containing a code. A code is a set of rules and symbols used to carry information.

• To understand how DNA functions, you first need to learn about the structure of the DNA molecule.


How was DNA discovered?

• Many scientists from all over the world contributed to our understanding of DNA.

• Some scientists discovered the chemicals that make it up.

• Other scientists learned about how these chemicals fit together.



Unraveling DNA


What does DNA look like?

• Experiments and imaging techniques have helped scientists to infer the shape of DNA.

• The structure of DNA is called a double helix.



• The two sides of the ladder shape are made of sugars and phosphate groups.

• The rungs of a DNA strand are made of pairs of bases.




• The building block of DNA is called a nucleotide, which is a base, a sugar, and a phosphate group.

• There are four different nucleotides in DNA.




• The bases in nucleotides are paired, or complementary.

• Adenine always pairs with thymine (A-T).

• Cytosine always pairs with guanine (C-G).

• The order of the nucleotides in DNA is a code that carries information.




• Genes are segments of DNA that relate to a certain trait.

• The code in the nucleotide order has information about which proteins the cells should build.

• The types of proteins that your body makes help determine your traits.



Replication and Mutation


How are copies of DNA made?

• The cell makes copies of DNA molecules through a process known as replication.

• During replication, the DNA separates.

• The bases on each side are used as a pattern for a new strand.



• As replication proceeds, complementary nucleotides are added.

• When replication is complete, there are two identical DNA molecules.




• Describe what is happening in the diagram.



When are copies of DNA made?

• Before a cell divides, it copies its DNA.

• Our cells can replicate DNA in just a few hours, because replication begins in many places along a DNA strand.

• Many groups of proteins are working to replicate your DNA at the same time.



What are mutations?

• Mutations are changes in the number, type, or order of bases on a piece of DNA.

• There are three main kinds of mutations: deletions, insertions, and substitutions.



What are mutations?

• In a deletion mutation, a base is left out.

• In an insertion mutation, an extra base is added.

• The most common mutation, substitution, happens when one base replaces another.



What are mutations?• Which type of

mutation is shown in each row?



What are mutations?

• Mutations can happen by random error, and also by damage to the DNA molecule by physical or chemical agents called mutagens.

• Cells make proteins that can fix errors in DNA, but sometimes the mistake is not corrected.

• The mistake then becomes part of the genetic code.



What are mutations?

• A genetic disorder results from mutations that harm the normal function of the cell.

• Some harmful mutations are inherited, or passed on from parent to offspring. Others can lead to cancer.



Protein Factory


What is the role of DNA and RNA in building proteins?• To build proteins, some of the information in the

DNA is copied to a separate molecule called RNA, or ribonucleic acid.

• RNA is used to build proteins.


What is the role of DNA and RNA in building proteins?• Like DNA, RNA has a sugar-phosphate backbone

and the bases adenine (A), guanine (G), and cytosine (C).

• Instead of thymine (T), RNA contains uracil (U).

• There are three types of RNA. Each type has a special role in making proteins.



What is the role of DNA and RNA in building proteins?• When a cell needs to make a protein, it makes an

RNA copy of a section of the DNA. This is called transcription.

• In transcription, DNA is used as a template to make a complementary strand of messenger RNA (mRNA).

• The information in the mRNA is then used to build proteins. This is called translation.



What is the role of DNA and RNA in building proteins?• In translation, the mRNA passes through a protein

assembly line within a ribosome.



What is the role of DNA and RNA in building proteins?• A ribosome is a cell organelle made of ribosomal

RNA (rRNA) and protein.

• As mRNA passes through, transfer RNA (tRNA) delivers amino acids to the ribosomes.

• The order of the bases codes for which amino acid is attached.

• The amino acids are joined together to form a protein.



Science

U8L1 DNA Structure & Function