CHAPTER 17 Molecular Genetics

Why do Animals look the same?

17.1DNA 17.2Genes Chapter 17 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 DNA

A cell contains a nucleus and in the nucleus are chromatin strands that are made up of proteins and deoxyribonucleic acid (DNA). an animal cell nucleus with chromatin strands inside DNA molecule protein molecules 17.1 DNA

How is DNA organised inside the cell nucleus? Each DNA molecule consists of two parallel strands twisted around each other to form a double helix. During cell division, the chromatin threads coil more tightly to form chromosomes inside the cell nucleus. A molecule of DNA is wrapped around proteins to form a single chromatin thread DNA

What is DNA? A molecule that carries genetic information. It is made up of nucleotides. A nucleotide is made up of: (1) a deoxyribose (sugar) molecule, (2) a phosphate group, and (3) a nitrogen-containing base - adenine (A), thymine (T), guanine (G), or cytosine (C) DNA

Possible nucleotides that can be formed: adenine nucleotide thymine nucleotide guanine nucleotide cytosine nucleotide bases sugar-phosphate backbone polynucleotide These nucleotides can be joined together to form polynucleotides DNA

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 DNA

Rule of base pairing Adenine (A) bonds with thymine (T) Guanine (G) bonds with cytosine (C) These pairs of bases are called complementary bases. Adenine (A) and thymine (T) are complementary bases. Guanine (G) and cytosine (C) are complementary bases DNA

The two anti-parallel strands of the DNA molecule coil to form a double helix structure. bases sugar-phosphate backbone coiling of DNA the double helix structure of DNA 17.1 DNA

Mini project Edwin Chargaff was the biochemist who discovered that: the percentage of adenine = the percentage of thymine and the percentage of guanine = the percentage of cytosine in the DNA of a cell. Find out more about Edwin Chargaff and his contributions to molecular genetics. Prepare a poster and a short presentation on your findings DNA

Checkpoint 2.State the complementary base pair to the strand shown below: Answer: 1.DNA molecules found in the cell nucleus are compacted to form chromatin strands. Other than DNA, what other molecule is found in chromatin strands? Answer: Protein molecules 17.1 DNA

3. State the ratio of: (1) adenine : thymine, and (2) guanine : cytosine in the DNA of a cell. Answer: (1)1 : 1 (2)1 : 1 4.The strands in a DNA molecule are ___________. The strands coil together to form a ______ ______ structure. anti-parallel double helix 17.1 DNA

REMINDER Nucleotide

17.1DNA 17.2Genes Chapter 17 Molecular Genetics

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 Genes

The Eye Colour is Green due to proteins. Proteins are formed thanks to genes found in the DNA that encodes for eye colour. Over time, eye colour may change (either lighten or darken) This is due to different expressions of the gene which leads to different release of proteins thus a different colour!

What is a gene? It is a segment of DNA. The nucleotide sequence in the gene determines the protein formed thus the hereditary trait. Since there are four different nucleotides, for a gene made up of n nucleotides, there are 4 n different combinations of nucleotides. gene DNA polypeptide coded by the gene 17.2 Genes

Three nucleotides in a gene form a codon and each codon codes for one amino acid. The genetic code states which amino acid each codon codes for. Example: Codon (DNA) Amino acid coded for TACMethionine (M) TATAlanine (A) CATLysine (K) GAGGlutamic acid (E) ACASerine (S) 17.2 Genes

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 16. Can you state the two examples? (1)Albinism (2)Sickle-cell anaemia What happens when the nucleotide sequence in a gene is altered? 17.2 Genes

Gene mutation refers to the change in genetic material of a gene. Examples of gene mutation: (1) Albinism - mutation in the gene causes an absence or defect in the enzyme that produces pigment Revision (2) Sickle-cell anaemia - mutation in the gene causes the protein product to differ from the normal protein by a single amino acid, causing red blood cells to be sickle- shaped 17.2 Genes

How are proteins made?

The DNA template is first transcribed into a messenger RNA (mRNA) molecule through a process called transcription. Transcription occurs in the nucleus of the cell. During transcription, the DNA codons in the gene are converted into RNA codons. The mRNA molecule is then translated into polypeptides through the process of translation. Translation occurs in the cytoplasm of the cell. How are proteins made? 17.2 Genes

DNA template transcription mRNA - RNA contains uracil (U) instead of thymine (T) polypeptide translation 17.2 Genes

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 17.2 Genes

17.2 Transcription and Translation Genes 1 2 template strand gene unzips transcription ribosome mRNA mRNA molecule 3 attachment to ribosome

Translation Attachment of the mRNA to a ribosome is the start of the translation process. The codons on the mRNA tells the cell what amino acids to attach together and in what order. peptide bond amino acids attached to tRNA ribosome codon 17.2 Genes

Attachment of mRNA with ribosome mRNA is then read by codons (every 3 bases) Bases found on mRNA will be complementary to tRNA (transfer) bases. Thus, formation of polypeptide chain begins with bonding of other tRNA (different amino acids). Polypeptide chain elongates with reading of every 3 bases on mRNA by ribosome. It will elongate till it reaches the termination codon found on mRNA. Once completed, ribosome shall release mRNA and protein is released into cytoplasm for processing.

Chapter 17 Molecular Genetics

Genetic engineering: an example Genetic Engineering

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

The process Isolate the desired gene Insert the gene into the vector DNA Insert the recombinant DNA into bacteria Genetic Engineering

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. Genetic Engineering

insulin gene cut using restriction enzyme DNA fragment that contains the insulin gene Isolating the human insulin gene 1 Genetic Engineering

Inserting the gene into the vector 2 cut by same restriction enzyme sticky ends insulin gene inserted into plasmid insulin gene bacterial plasmid Genetic Engineering

Inserting the recombinant plasmids into bacteria 3 recombinant plasmid (bacterial plasmid with human insulin gene inserted) bacterial DNA recombinant plasmid transgenic bacterium Genetic Engineering

Activity Have you heard of the term ‘designer babies’? Find out more about more about designer babies on the Internet and prepare a presentation on it. Genetic Engineering