Sections 12.3, 13.1, 13.2

Transcription

1 Sections 12.3, 13.1, 13.2

2 Background: Watson & Crick recognized that base pairing in the double helix allows DNA to be copied, or replicated Each strand in the double helix has all the information to remake the other strand DNA strands are called complementary because they can be used to make the other strand

3 Replication: the process of copying DNA before cell division To begin, the DNA molecule separates into two strands Starting molecule: Double stranded DNA

4 Overall, what happens? DNA makes an exact copy of itself before cell division can occur Because it is DNA, only the nitrogenous bases adenine, guanine, thymine, and cytosine can be used

5 Steps in DNA Replication: 1. The two strands of DNA separate 2. Each strand serves as a template 3. New nucleotides are added to each of the single DNA strands rules of base pairing are followed for DNA (A-T, C-G) 4. Two identical DNA molecules are formed

6 Original Strand of DNA A T G T T C G G A A C T T A C A A G C C T T G A Top Strand (DNA) A T G T T C G G A A C T Bottom Strand (DNA) T A C A A G C C T T G A

7 Ending molecules: two identical DNA molecules that are the same as each other and to the original starting strand Where does this take place? Inside the cell s nucleus

8 Now that the DNA has been copied, it needs to send its genetic message to the ribosomes so proteins can be made Transcription: synthesis (making of) an RNA molecule from a DNA template DNA is too big to leave the nucleus, so it sends it message using RNA to the ribosomes in the cytoplasm

9 Starting molecule: double-stranded DNA Overall, what happens? Segments of DNA serve as templates to make complementary RNA molecules The nitrogenous bases used in the DNA strand are: adenine, thymine, guanine, cytosine The nitrogenous bases used in the RNA strand are: adenine, uracil, guanine, cytosine

10 Steps in Transcription: 1. The two strands of DNA separate 2. Each strand serves as a template 3. New nucleotides form a strand of mrna that is complementary to the starting DNA strand (use base pairing rules for RNA)

11 Original Strand of DNA A T G T T C G G A A C T T A C A A G C C T T G A Top Strand (DNA) A T G T T C G G A A C T Bottom Strand (DNA) Complementary mrna strand T A C A A G C C T T G A

12 Ending molecule: single stranded mrna Where does this take place in the cell? In the cell s nucleus

13 The diagram shows the entire process of protein synthesis. Questions: 1. What structure is A pointing to? 2. What is structure B? How do you know? 3. Which process is taking place as structure B leaves structure A?

14 One of the many functions of the cell is to produce proteins that direct cellular activities Now that the DNA message has been transcribed into mrna, the message must be read, or translated, by the ribosome so the proteins can be made Translation: The process of decoding a mrna message into a protein

15 Starting molecule: single-stranded mrna Overall, what happens? Ribosomes read the mrna sequence, complementary trna binds the mrna, and the trna adds its amino acids to the polypeptide chain The nitrogenous bases used in the RNA strands are: adenine, uracil, guanine, cytosine

16 What is a codon? A codon is made of three consecutive bases that specify a single amino acid A U G U U C G G A A C U 1. First codon: 2. Second codon: 3. Third codon: 4. Fourth codon:

17 How do you read a codon? 1. Find the first letter of the codon in the center circle of the chart. 2. Find the second letter of the codon in the next ring on the chart, next to the first letter. 3. Find the third letter of the codon in the outer ring on the chart, and determine the amino acid that will be made.

18 Steps in Translation: 1. mrna travels from the nucleus to the cytoplasm, where it reaches a ribosome 2. Translation begins at AUG, the START codon. The ribosome recognizes this codon, and attracts the anticodon on a complementary trna molecule. 3. The ribosome shifts down the mrna strand, binding the next codon and anticodon. 4. The ribosome joins the two amino acids together and releases the trnas that brought them there. 5. The ribosome continues this process, forming a polypeptide chain.

19 Translation of the mrna message by the ribosome continues until the ribosome reaches one of the three STOP codons. At this time, the mrna and the polypeptide are released. Ending molecule: a protein is made (polypeptide) Where does this take place in the cell? On the ribosomes in the cytoplasm

20 Fill in the complementary trna that will match up to the mrna strand below. When using the codon chart to identify amino acids, be sure to use the mrna strand! Complementary trna A U G U U C G G A A C U Ribosome mrna strand

21 Use the mrna strand to find the first 4 amino acids: Complementary trna A U G U U C G G A A C U Ribosome mrna strand

22 The diagram shows the entire process of protein synthesis. Questions: 1. What structure is C pointing to? 2. What is structure D? 3. What is structure E?

23 The diagram shows the entire process of protein synthesis. Questions: 4. What structure is F pointing to? 5. What is structure G? 6. What process is happening as structure C reads structure G?

24 Use the diagram to help you answer the questions below. 1. The structures labeled A and B are called. 2. Structure C is cytosine, which is a type of.

25 Use the diagram to help you answer the questions below. 3. The structure labeled D is. 4. Structure E has three letters, which is known in general as a.

26 Use the diagram to help you answer the questions below. 5. The specific name for structure E is. 6. Structure F is another example of a.

27 Use the diagram to help you answer the questions below. 7. Which of the amino acids will be made by structure E?. 8. The process shown by arrow X is called.

28 Use the diagram to help you answer the questions below. 9. The process shown by arrow Y is. 10. Together, the processes shown by X and Y are called.