molecular genetics 2014

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Learning Objectives:

(a) outline the relationship between DNA, genes and chromosomes.

(b) state the structure of DNA in terms of the bases, sugar and phosphate groups found in each of their nucleotides.

(c) state the rule of complementary base pairing.

(d) state that DNA is used to carry the genetic code, which is used to synthesise specific polypeptides.

(e) state that each gene is a sequence of nucleotides, as part of a DNA molecule.

(f) explain that genes may be transferred between cells

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Learning Objectives:

(g) briefly explain how a gene that controls the production of human insulin can be inserted into bacterial DNA to produce human insulin in medical biotechnology.

(h) outline the process of large-scale production of insulin using fermenters.

(i) discuss the social and ethical implications of genetic engineering, with reference to a named example.

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"Cloning is all very well in theory, but do you have any proof it can actually work?"

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1. We inherit traits from aunts, uncles, cousins and siblings because family members point out the resemblance between students and their relatives.

2. Some people think that most common traits are “better”.

3. Dominant alleles or traits are always the most common.

4. DNA is a living thing.

5. Only animal contains DNA.

6. Genes from one type organism will not function in a different type organism.

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1. Traits can only be inherited from parents, and by extension, grandparents.

2. No. The traits simply show up more frequently in the human population.

3. Not necessary. ( A dominant trait may be quite rare, while a recessive trait

may be the most common one observed.)

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× DNA is a living thing.

× Genes from one type organism will not function in a different type organism.

× Only animal cells contain DNA.

4. DNA is a molecule with instructions for a cell.

5. Plants also contain DNA

6. There is a genetic code common to all living things.

20.1 DNA

20.2 Genes

20.3 Transferring Genes between Organisms

20.4 Effects of Genetic Engineering on Society

Chapter 20 Molecular Genetics

Learning Outcomes

After this section, you should be able to:

• describe the basic unit of DNA – the nucleotide;

• state and apply the rule of complementary base pairing.

20.1 DNA

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Chromosomes

• Inheritable materials in nucleus of a cell. Numerous genes are located on it.

• Chromosomes can exist in coiled compact form or uncoiled extended form.

• Cells undergoing cell division will contain chromosomes in coiled compact form.

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Function of DNA

• It codes for the synthesis of polypeptides.

• Many polypeptides will join together to form protein, which is responsible for your traits.

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Structure of DNA

• A molecule that carries genetic information

• The basic unit of DNA is known as nucleotide;

Video:http://www.youtube.com/watch?v=ubq4eu_TDFc

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adenine nucleotide

thyminenucleotide

guaninenucleotide

cytosinenucleotide

• Each nucleotide (basic unit) is a complex of three subunits:

a) a sugar (deoxyribose/ribose)b) a phosphate groupc) a nitrogenous base

• Many nucleotides can be joined together to form polynucleotides.

adenine nucleotide

thymine nucleotide

guanine nucleotide

cytosine nucleotide

bases

sugar-phosphate backbone

polynucleotide

“Rule of base pairing”

• Adenine (A) bonds with thymine (T)

• Guanine (G) bonds with cytosine (C)

These pairs of bases are called complementary bases.

• The DNA molecule is made of two anti-parallel polynucleotide strands. (The two strands run in opposite directions.)

• The bases on one strand form bonds with the bases on the other strand according to the rule of base pairing.

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Animation: DNA Structure

The two anti-parallel strands of the DNA molecule coil to form a double helix three-dimensional structure.

bases

sugar-phosphate backbone

coiling of DNA

the double helix 3D structure of DNA

Coiling of DNA

Uncoiled DNA resemble a ladder

(2D structure)

Coiled DNA resemble a spiral

staircase/ double-helix

(3D structure)

Coiling of DNA

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Activity: Build Your DNA Model

• Create a DNA model using materials of their own choice.

• Suggested materials include straws, pipe cleaners, pasta

• They should include a key that explains what each item represents. After you have completed their models, display the models to the whole class.

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Examples:

http://luehy.wikispaces.com/DNA+Pasta

Checkpoint 1

1. a) State the bases that are complementary to the bases on strand shown below:

b) State the ratio of:

(1) adenine : thymine, and

(2) guanine : cytosine

in the DNA of a cell.

Answer:

Answer:

(1)1 : 1

(2)1 : 1

• What is the base sequence of the DNA strand that would be complementary to the following single-stranded DNA molecule?

GGATCTGATCCAGTCA

A : GGAUCUGAUCCAGUCA

B : CCTAGACTAGGTCAGT

Checkpoint 2

• The percent of cytosine in a double-stranded DNA is 21. What is the percent of thymine in that DNA?

A 21%

B 29%

Checkpoint 3

• According to base pair rule, the percentage of As, Ts, Cs, and Gs should add up to 100%, because

A

C

T

G

=

=

Adding all the bases together should make up 100% of the DNA molecule.

• The percent of adenine in a double-stranded DNA is 38.

What is the percent of cytosine in that DNA?

A 12%

B 38%

Checkpoint 4

• The percent of guanine in a double-stranded DNA is 14. What is the percent of adenine in that DNA?

A 14%

B 36%

Checkpoint 5

© Boardworks Ltd 2004

What’s the order? Let’s Recap !

Let’s Recap !

Investigation 13.2 : DNA Extraction of Onion

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Add 10cm3 detergent To break nuclear

membrane

Add 10cm3 of ethanol To separate out the

DNA strand

Add phenol red indicator Indicate presence of DNA

20.1 DNA

20.2 Genes

20.3 Transferring Genes between Organisms

20.4 Effects of Genetic Engineering on Society

Chapter 20

Learning Outcomes

After this section, you should be able to:

• state that DNA molecules contain the genetic code;

• state what is meant by the genetic code;

• state that a gene is a specific sequence of nucleotides in a DNA molecule that controls the production of a polypeptide.

20.2 Genes

What is a gene?

• It is a segment of DNA.

• The nucleotide sequence in the gene determines the polypeptide formed.

gene

DNA

polypeptide coded by the gene

20.2

• Three bases, or codon, code for one amino acid.

• A chain of amino acids makes up one polypeptide, which later can be used to make proteins.

Codonon DNA

Example of amino acid coded for

TAC Methionine (M)

TAT Alanine (A)

CAT Lysine (K)

GAG Glutamic acid (E)

ACA Serine (S)

“One gene, one polypeptide” theory

• The theory that each gene is responsible for the synthesis of a single polypeptide

What happens when the nucleotide

sequence in a gene is altered?

What happens when the nucleotide

sequence in a gene is altered?

A change in the nucleotide sequence of a gene is termed as gene mutation.

A mutation may or may not lead to a change in the protein product.

A change in the protein product may or may not lead to an observable phenotype.

Recall

Two examples of gene mutation was mentioned in Chapter 19. Can you state the two examples?

(1)Albinism

(2)Sickle-cell anaemia

Important!•A cell cannot directly use the DNA template to make proteins. It has to go through the following stages.

How are proteins made?

How are proteins made?

(a) Transcription: • Messages in DNA template is copied into

messenger RNA in the nucleus.

• (b) Translation : messenger RNA carries the message to cytoplasm and ribosome helps to convert them into proteins.

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(a) Transcription

(b) Translation

MicroQuestions1. Describe the relationship between DNA, genes

and chromosome. [3]

2. Using the idea of molecular structure, describe the structure of DNA and its function in leading to a trait. [4]

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1) (a)•Gene is a segment of the DNA molecule .

•Chromosomes are made of coiled DNA molecules.

•DNA carries many genes along its length.

1) (b)

Function:

DNA codes for the synthesis of polypeptide.

Polypeptides are used to make proteins , which are responsible for many traits.

Structure of DNA: • Basic unit made of nucleotide• Nucleotide is made a phosphate group, a sugar and a

base.

• The 2 strands of polynucleotide joined together by the ‘complementary base pairing rule’ (A & T , G & C)

• 2 strands are twisted to form a double helix 3D structure

DNA template

transcription

mRNA - RNA contains

uracil (U) instead of thymine (T)

polypeptide

translation

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It is a temporary molecule that is made when needed.

It is a permanent molecule in the nucleus.

It is a small soluble molecule.It is a large insoluble molecule.

No fixed ratio between A and U and between G and C.

Ratio of A:T and G:C is 1:1.

Nitrogen-containing bases are adenine (A), uracil (U), guanine (G) and cytosine (C).

Nitrogen-containing bases are adenine (A), thymine (T), guanine (G) and cytosine (C).

Sugar unit is ribose.Sugar unit is deoxyribose.

RNADNA (double helix)

DNA vs. RNA

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Transcription and translation

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2

template strand gene unzips

transcription

ribosome

mRNA

mRNA molecule

3 attachment to ribosome

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The biological molecules involved are:(1) Amino acids

- There are a total of 20 different amino acids.

(2) Transfer RNA (tRNA) molecules- Each tRNA molecule has an amino acid attached.- The amino acid attached depends on the tRNA’s anticodon.

(3) Ribosomes- Ribosomes help make polypeptides from mRNA molecules.

(4) mRNA molecules

Translation

anticodon

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Translation

peptide bondamino acids attached to tRNA

ribosome

codon

first tRNA is released

a new tRNA fits into the ribosome

ribosome moves along the mRNA strand

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2

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3 polypeptide formed

stop codon

Amino acids are continually attached until the ribosome reaches the stop codon on the mRNA.

Upon encountering the stop codon, the ribosome leaves the mRNA.

The complete polypeptide is produced.

URL

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20.1 DNA

20.2 Genes

20.3 Transferring Genes between Organisms

20.4 Effects of Genetic Engineering on Society

Chapter 20

Pure Biology

Learning Outcomes

After this section, you should be able to:

• define genetic engineering;

• describe human insulin production as an example of an application of genetic engineering;

• differentiate between selective breeding and genetic engineering.

20.3

Pure Biology

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“Pigs that glow in the dark””

• The scientists will use the transgenic pigs to study human disease.

• Because the pig's genetic material encodes a protein that shows up as green, it is easy to spot.

http://science.howstuffworks.com/framed.htm?parent=question388.htm&url=http://news.bbc.co.uk/1/hi/world/asia-pacific/4605202.stm

• Genetic engineering refers to the manipulation of an organism’s genetic material.

• It involves the transfer of genes from one organism to another.

• This is done by the use of a vector.

• A vector molecule is DNA molecule that is used to carry the gene or genes to be transferred.

• Plasmids (circular DNA) from bacteria are commonly used as vectors.

Genetic engineering

The process

Isolate the desired gene

- Cut the gene using restriction enzymes.

Insert the gene into the vector DNA

- Restriction enzymes that were used to cut the desired gene are used to cut the vector DNA.

- Both the cut vector DNA and gene are mixed together with DNA ligase, an enzyme that will help join the two molecules together.

Insert the recombinant plasmids into bacteria

- Mix recombinant plasmids with bacteria and heat- or electric-shock the cells.

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2

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20.3

• Mass production of human insulin for type 1 diabetes patients was made possible through the use of genetic engineering.

• The human insulin gene is transferred to bacterial cells that are able to express the gene. The product (insulin) can then be harvested.

Producing human insulin

Background:Type 1 diabetes is caused by the inability of the islets of Langerhans to produce sufficient insulin.

insulin gene

cut using restriction enzyme

sticky end

DNA fragment that contains the insulin gene

Isolating the human insulin gene1

Inserting the gene into the vector2

cut by same restriction enzyme

sticky ends

insulin gene inserted into plasmid

insulin gene

bacterial plasmid

Inserting the recombinant plasmids into bacteria

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recombinant plasmid (bacterial plasmid with

human insulin gene inserted)

bacterial DNA

recombinant plasmid

transgenic bacterium

• The transgenic bacteria need to be burst open in order to extract the human insulin that is produced in the bacteria.

• In order to obtain large amounts of human insulin, large amounts of transgenic bacteria need to be cultured.

• This is done through the use of large sterile containers called fermenters.

Large-scale production of human insulin

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Mass production of insulin in a

fermenter

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• Creation of transgenic plants that are resistant to herbicides.

• Creation of transgenic plants that are pest-resistant.

• Gene therapy – healthy genes can be transferred from one person to the cells of another person with defective genes.

Other applications of genetic engineering

20.3

• Genes can be transferred between organisms of different species (as shown in the production of insulin) and between organisms of the same species.

• An example of gene transfer between organisms of the same species is the transfer of a pest-resistant gene from wild wheat plants to common wheat plants that are grown as crop.

Note that:

20.3

Selective breeding vs. genetic engineering

More efficient as transgenic organisms grow faster and may require less food

Less efficient as organisms grow more slowly and may require more food

A process which uses individual cells that reproduce rapidly in a small container in a laboratory.

Slow process that involves several generations.

Selection of genes before transfer eliminates the risk of transferring a defective gene.

There is a possibility that defective genes will be transmitted to the offspring.

Genes from an organism can be inserted into non-related species or different species.

Organisms involved in selective breeding must be closely related or of the same species.

Genetic engineeringSelective breeding

20.1 DNA

20.2 Genes

20.3 Transferring Genes between Organisms

20.4 Effects of Genetic Engineering on Society

Chapter 20

Molecular Genetics

Learning Outcomes

After this section, you should be able to:

• discuss the advantages and disadvantages of genetic engineering;

• state the social and ethical implications of this technology.

Advantages of genetic engineering

Nutritional quality of foods are improved.

Development of foods designed to meet specific nutritional goals

The use of costly pesticides that may damage the environment is reduced.

Development of pesticide-resistant crops

Farmers are able to grow crops in environmental conditions that are not favorable for cultivating most crops.

Production of crops that grow in extreme conditions

Drugs like human insulin become more affordable.

Low cost production of medicines

Benefits to societyApplications of genetic engineering

Disadvantages of genetic engineering

Environmental hazards

• Genetically-modified (GM) crop plants that produce insect toxins may result in the deaths of insects that feed on them and may result in loss of biodiversity.

Economic hazards

• If the prices of the seeds of modified crop plants are not regulated, poorer farmers may not have the financial capacity to benefit from this technology while richer farmers continue to get richer through the technology.

Disadvantages of genetic engineering

Social and ethical hazards• Genetic engineering may lead to class distinctions.• Some religions do not approve of genetic engineering as

it may not be appropriate to alter the natural genetic make-up of organisms.

Health hazards• Genes that code for antibiotic resistance may be

accidentally incorporated into bacteria that cause human diseases.