U2L6 DNA Structure and Function Notes DNA Structur… · • When a cell needs to make a protein,...

Unit 2 Lesson 6 DNA Structure and Function

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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 up DNA, and others learned how these chemicals fit together.

• Still others determined the three-dimensional structure of the DNA molecule.



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 a twisted ladder shape called a double helix.



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

• The rungs of the ladder are made of pairs of bases.




• A base, a sugar, and a phosphate group make a building block of DNA called a nucleotide.

• 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 two strands of DNA separate.

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



• As bases on the original molecule are exposed, 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? (The first row is the original sequence.)



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 genetic disorders are inherited, or passed on from parent to offspring.

• Other disorders result from mutations during a person’s lifetime. Most cancers fall in this category.



Protein Factory


What is the role of DNA and RNA in building 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).

• Three types of RNA have special roles 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.



U2L6 DNA Structure and Function Notes DNA Structur… · • When a cell needs to make a protein,...

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