Name___________________________________

Unit 5A Gene Expression

13.1 RNA (Textbook pages 362-365)

Lesson Objectives- At the end of the lesson, you should be able to:

1. Contrast RNA and DNA.2. Explain the process of transcription.

https://youtu.be/h5mJbP23Buo

A. The Role of RNARNA (ribonucleic acid) is a nucleic acid like DNA. It consists of a long chain of nucleotides. The RNA base

sequence directs the production of proteins – RNA puts the genetic code into action. Ultimately, cell proteins result in phenotypic traits.

The main differences between RNA and DNA are:

1. The sugar in RNA is *__________________ instead of deoxyribose. 2. RNA is generally *_____________-stranded and not double-stranded like DNA.3. RNA contains *_____________ in place of thymine.

RNA can be thought of as a disposable copy of a segment of DNA. Most RNA molecules are involved in protein synthesis. The three main types of RNA are:

1. Messenger RNA (mRNA)

2. Ribosomal RNA (rRNA)

3. Transfer RNA (tRNA)

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B. RNA Synthesis (Transcription) - https://www.youtube.com/watch?v=ztPkv7wc3yU&safe=active

Most of the work of making RNA takes place during transcription. In transcription, segments of DNA serve as templates to produce complementary RNA molecules.

1. In prokaryotes, RNA synthesis and protein synthesis takes place in the *______________________.

2. In eukaryotes, RNA is produced in the cell’s *_____________ and then moves to the *_______________________ to play a role in the production of protein.

The following focuses on Transcription in eukaryotic cells.

1.The enzyme *_____________________ binds to DNA during transcription and separates the DNA strands. It then uses one strand of DNA as a template from which to assemble nucleotides into a complementary strand of RNA. This strand of DNA is called the “sense” strand.

1. The instructions for assembling proteins are contained in theA. genes.B. ribosomes.C. cytoplasm

2. The central dogma of molecular biology is that information is transferred fromA.DNA to protein to RNA.B. protein to DNA to RNA.C. DNA to RNA to protein.

3. The way in which DNA, RNA, and proteins are all involved in putting genetic information into action in living cells is calledA. translation.B. transcription.C. gene expression.

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13.2 Ribosomes and Protein Synthesis (Textbook pages 366-371)

Lesson Objectives- At the end of the lesson, you should be able to:1. Identify the genetic code and explain how it is read.2. Summarize the process of translation. - https://www.youtube.com/watch?v=B6O6uRb1D38

3. Describe the “central dogma” of molecular biology.

A. The Genetic Code A specific sequence of bases in DNA carries the directions for forming a *___________________, a chain of amino acids.

The types and order of amino acids in a polypeptide determine the properties of the protein. The sequence of bases in mRNA is the genetic code.

The four bases, *______ *______ *______ *_____ , act as “letters.”

The code is read three “letters” at a time, so that each “word” is three bases long and corresponds to a single amino acid. Each three-letter “word” in mRNA is known as a *__________________

Because there are four different bases in RNA, there are *_______ possible three-base codons in the genetic code. (43).

How many different amino acids are there?*_____With the exception of Methionine and Tryptophan, there is more than one triplet for each amino acid.

Decoding for us is made easier by use of a genetic code table. (See pages 14 and 15 for Codon Charts)

NOTE: Some codons serve as “start” and “stop” signals for protein synthesis.

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B. Translation Ribosomes use the sequence of codons in mRNA to assemble amino acids into polypeptide chains. The process of decoding of an mRNA message into a protein is translation.

Messenger RNA is transcribed in the nucleus and then enters the * .

On the ribosome, translation begins at the *___________________. Each codon attracts an *___________________, the complementary sequence of bases on tRNA.

Each tRNA carries one kind of *______________ _____________. The match between the codon and anticodon ensures that the correct amino acid is added to the growing chain.

The amino acids bond together, each in turn. The ribosome moves along the mRNA, exposing codons that attract still more tRNAs with their attached amino acids.

The process concludes when a *___________ _____________is reached. The newly formed polypeptide and the mRNA molecule are released from the ribosome.

The Steps to Translation

Prior to translation, the mRNA is transcribed in the nucleus – then enters the cytoplasm.

1. Translation begins when a ribosome attaches to an mRNA molecule in the cytoplasm.

As the ribosome reads each codon of mRNA, it directs tRNA to bring the specified amino acid into the ribosome.

One at a time, the ribosome then attaches each amino acid to the growing chain.

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2. Each tRNA molecule carries just one kind of *

In addition, each tRNA molecule has three unpaired bases, collectively called the anticodon—which is complementary to one mRNA codon.

The tRNA molecule for methionine (AUG) has the anticodon *________________.

3. The ribosome has a second binding site for a tRNA molecule for the next codon.

If that next codon is UUC, a tRNA molecule with an AAG anticodon brings the amino acid phenylalanine into the ribosome. (see image above)

4. The ribosome helps form a peptide bond between the first and second amino acids—methionine and phenylalanine.

At the same time, the bond holding the first tRNA molecule to its amino acid is broken.

5. That tRNA then moves into a third binding site, from which it exits the ribosome. (see image above)

The ribosome then moves to the third codon, where tRNA brings it the amino acid specified by the third codon (in this example, Lysine).

6. The polypeptide chain continues to grow until the ribosome reaches a “stop” codon on the mRNA molecule.

When the ribosome reaches a stop codon, it releases both the newly formed polypeptide and the mRNA molecule, completing the process of translation.

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Think about it:

Which direction is the mRNA moving through the ribosome? Label it on the diagram.

Which direction is the polypeptide growing ? Label it on the diagram.

What are the four types of molecules required for translation?

1._____________________________________________________

2._____________________________________________________

3. _____________________________________________________

4. _____________________________________________________

C. The Molecular Basis of Heredity

1. Molecular biology seeks to explain living organisms by studying them at the molecular level, using molecules like DNA and RNA.

2. The central dogma of molecular biology is that information is transferred from DNA to RNA to protein.*___________ *___________ *__________________ *__________________

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1. Gene expression is the way in which DNA, RNA, and proteins are involved in putting genetic information into action in living cells.

The genetic code is generally *( the same/ different ) in all organisms. The genetic code is said to be “Universal”.

13.3 Mutations (Textbook pages 372-376) https://youtu.be/GieZ3pk9YVoLesson Objectives- At the end of the lesson, you should be able to:1. Define mutations and describe the different types of mutations.2. Describe and predict the effects different mutations can have on genes.

*Think about it: The sequence of bases in DNA is like the letters of a coded message. What would happen if a few of those letters changed accidently, altering the message? Could the cell still understand its meaning?

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______________________________________________________________________________________________ What effects do you predict these changes would have on genes and the polypeptides for which they code? ______

____________________________________________________________________________________________________________________________________________________________________________________________________

A. Types of Mutations Mutations are *_______________________________________________________.

There are two categories of mutations:

1. * ____ _______________ produce changes in a single gene. Such mutations involve*___________ or a *____________ _______________. These mutations generally occur during *________________________. If a gene in one cell is altered, the alteration can be passed on to every cell that develops from the original one.

*________________, *________________, and *__________________________ are all types of point mutations.1.In a substitution, *________ ________ is changed to a *____________ __________, which may affect only a

single amino acid and have no effect at all.2.In insertions and deletions, one base is inserted or removed from the DNA sequence. Insertions and deletions are

called *_______________ _____________ because they shift the “reading frame” of the genetic message. Such mutations can change every amino acid that follows the point of mutation and can have dramatic effects on the organism.

*Stop and Review: Which type of point mutation affects only a single amino acid in protein?______________Is this always harmful? _________________Which type of point mutation can affect more than one amino acid? _________________Is this usually harmful?_______________________Identify the type of mutation that changes the word “milk” to “mile”:________________

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2. The second category of mutations are *__________________ ________________ which produce changes in the number or structure of chromosomes. They include _____________, ________________, ________________, and _________________________.

1.*_________________ involves the loss of all or part of a chromosome.

2.* ________________ produces an extra copy of all or part of a chromosome.

3.* ________________ reverses the direction of parts of a chromosome.

4.* ________________ occurs when part of one chromosome breaks off and attaches to another.

B. Effects of Mutations

Genetic material can be altered by *__________ ____________ or by *____________ ______________.

Many errors can be made during * _______________ _____________, specifically, replication. The cellular machinery that replicates DNA inserts an incorrect base roughly every *__________________________ bases.Stressful *_________________ conditions may also increase the rate of mutation in certain organisms.

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*______________________________ are chemical or physical agents in the environment that cause mutations.

Examples of Chemical agents that cause mutations Examples of Physical agents that cause mutations* *

The effects of mutations on genes vary widely:1. Some mutations have *______________ or ___________effect.2. Some mutations produce *_________________________variations. One example is polyploidy in plants, in

which an organism has *___________ _________ of ____________. Polyploid plants are often larger and stronger than diploid plants. Mutations can also produce *_______________ with new or altered functions that can be useful to organisms in different or changing environments.

3. Some mutations *______________________ gene function or *__________________protein structure. Genetic disorders such as sickle cell disease or haemophilia are the result of inherited mutations.

*Think about it: An altered gene may be passed on to every cell that develops from it. But, in which cells must a mutation occur in order for the mutation to be passed on to the next generation of a sexually reproducing organism? _________________________________________________.

If you inherit a disease like sickle cell anemia, what are you actually inheriting?______________________________________________________________________________________________________________________________________________________________________________________________________________________________________

*Analogy: A mutation is like a ___________________________ because they both ______________________

Codon Charts

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