DNA and Genetics Dr André van Wyk UFS
38 46 • Somatic cells • Cells of the “Soma”= Body cells • Complete number of chromosomes = 2n • Diploid 48
2n 2n 2n Growth = 2n – 2n Mitosis 2n • Somatic cells • Cells of the “Soma”= Body cells • Complete number of chromosomes = • Diploid Mitosis: 2n = 2n or n – n this correct?
n n mitosis n
2n n 2n 2n – n Meiosis Sex cells = Half of the chromosome number = n = haploid cells Reduction of the chromosome number – a must for the survival of the species 2n n + n = 2n Haploid + Haploid = Diploid FERTILISATION
The importance of Meiosis: • The process of meiosis reduces the number of • chromosomes by half. • Meiosis is the process through which somatic cells (2n) • are changed into sex cells (n). • Meiosis ensures that the number of chromosomes in • the species stays the same over generations • Meiosis is important to introduce genetic variation.
DNA –Position in the cell DNA double helix Nucleus Chromosomes
In the nucleus of almost every cell in your body is the collection of DNA needed to make you. DNA in the nucleus is grouped into 23 sets (pairs) of chromosomes that are called your "genome." • In each chromosome, the DNA is grouped into • "genes." • Your genome contains about 35,000 genes.
Instructions to make your whole body and keep it working is contained in DNA • Instructions is called genetic code • The DNA in your genes tells the cell which • amino acids (protein building blocks) must • combine to make a protein. It also gives • instructions in which sequence the amino • acids must combine. • Thus, DNA provides the blueprint of all life in • a living body. • Let us investigate how that this happens.
DNA STRUCTURE • DNA molecule – double helix (ladder) • String of repeating molecules units called nucleotides • Each nucleotide consist out of - Deoxyribose sugar - One phosphate group - One nitrogen containing base (A,G,C and T) • Adenine and Guanine – purine bases • Thymine and Cytosine – pyrimidine bases
Remember Did you know : The total length of DNA in mammal cells is 2 metres – in your body 10 billion km
Structure of DNA Phosphate A T C G Deoxyribose Sugar Britannica video
It's hard to believe that an alphabet with only four letters can make something as wonderful and complex as a person
DNA Replication • With cell division -chromosome split in two (mitoses and meiosis ) • DNA must divide • DNA must make exact copies of itself • DNA molecule – unzip • New bases attached themselves in correct place of each strand • Each strand becomes a double helix • Sometimes mistakes happens – mutation • Mutations is important in evolution
DNA Replication Unzip into two single strands
DNA replication continue New bases attached themselves in the correct place of each strand Free nucleotides in nucleoplasm
Two identical strands are formed Each strand now becomes a double helix. Strand 1 Strand 2
Activity 1 • DNA structure and DNA replication • Group work. • Instructions - Use the package marked “DNA” and place the pieces together in order to: • Know the structure of DNA • Use the pieces and demonstrate the DNA replication process.
Significance of DNA replication: • Important for growth, reproduction • Mutations can cause variation • The main enzyme that catalyze the process is DNA polymerases • Forms building block for amino acids that forms proteins • Three bases provides more than the 20 combinations needed to code amino acids (p23) • The sequence of the three bases is called a codon.
Activity 2:Extraction of DNA (LO1) • Instructions : Use Worksheet 1 • Step 1 • Place ½ teaspoon of ground wheat in a spice jar. Add 10 teaspoons of tap water to the ground wheat and mix non-stop with a wooden stick for 3 minutes • Step 2 • Add ¼ teaspoon of dishwashing liquid to the cells that have been suspended in water in step 1. Mix gently with a wooden stick every ½ minutes for 5 minutes.
Step 3 • Remove all foam that may have formed on top of the mixture with a paper towel. Step 4 • Tilt the jar and slowly add an estimated equal volume of methylated spirit to the mixture and carefully pouring it down the side of the jar. Step 5 • Use the wooden sticks to fish these “white slimy threads” out of the spice jar and transfer it to a 10ml pill vial. Rubric You have extracted DNA
Assessment of DNA • Draw and label a diagram of DNA (LO1:AS2) (manipulate data) • Make a model of DNA – (LO1:AS3) ( Communicate data/findings) • Extraction of DNA out of wheat (LO1:AS2) • http://rubistar.4teachers.org(example rubric 1)
Questions on the DNA Molecule 1 G 2 3 T 4 5 • Identify the above molecule. • Give labels for parts numbered 1to 5 • 3. Describe how the above molecule • replicates itself. • Why is it of significance that this molecule can • replicate itself?
Bacterial DNA - Manufacturing of insulin • Diabetics need insulin to live • Diabetes use insulin from pigs and cattle. This is not the same as human insulin and sometimes produces side effects. With genetic engineering, bacteria are used to produce some human insulin
1. A string of DNA is taken from a bacterium 6. The insulin is collected and purified ready for use • The bacteria • reproduce, making clones of themselves • A piece is cut out using enzymes • as ‘chemical scissors’ 3. A cell is taken from a human pancreas. The gene for insulin is cut from the chromosome 4. The insulin gene is put into the string of bacteria DNA
U G A C Structure of RNA • Single strand • Sugar is ribose • Four nitrogen bases • Adenine and Uracil • Guanine and Cytosine Assessment : Make a stick drawing of RNA
Three types of RNA and their functions • 1. Messenger RNA (mRNA) which acts as a template for protein synthesis and has the same sequence of bases as the DNA strand that has the gene sequence. 1. Messenger RNA (mRNA) 2. Transfer RNA (tRNA) 3. Ribosomal RNA (rRNA)
2. Transfer RNA (tRNA), one for each triplet codon that codes for a pecific amino-acid (the building blocks of proteins). tRNA molecules are covalently attached to the corresponding amino-acid at one end, and at the other end they have a triplet sequence (called the anti-codon) that is complementary to the triplet codon on the mRNA. 3. Ribosomal RNA (rRNA) which make up an integral part of the ribosome, the protein synthesis machinery in the cell.
RNA Transcription • DNA is the template • DNA manufactures mRNA in nucleus • Transported out from the DNA of nucleus into the cytoplasm • Transcription similar to DNA replication
mRNA structure A C U U G A G C RNA bases pairing TRANSCRIPTION
tRNA Anticodon C C G G G C Codon mRNA mRNA` Crystal structure of tRNA molecules. The single-stranded chain is folded in a 'clover-leaf’
The process of translation and protein synthesis TRANSLATION TRANSCRIPTION mRNA moves to ribosome r RNA Amino acids linked up to form protein molecule tRNA carries amino acid to ribosome DNA unzip to expose a gene mRNA copies the gene
Protein synthesis in the cell Free amino acids tRNA brings amino acid to ribosome Ribosome incorporating amino acid in protein chain mRNA being translated
PROLINE G C U Assessment of RNA (LO2) • Describe the role of DNA and RNA in the following • 1.1 Formation of mRNA by transcription • 1.2 Movement of mRNA from the nucleus to cytoplasm • 1.3 Translation of mRNA (codon) to form protein using tRNA (anticodon) • Determine the sequence of bases in mRNA from DNA molecule. GTA ATG TGG TTT 3. Give the mRNA sequence that matched the anticodons of the tRNA
Activity 2 • Transcription and translation. • Group work. • Instructions - Use the package marked “Protein synthesis” and imitate the processes of transcription and translation with the pieces in the pack.
Protein synthesis (assessment) 1. 2 3 4 6 5 7 • Give labels for number 1 to 7 • Describe the processes that occur at numbers 2,3,5
Mitoses Mitoses • Revision: • Group work: • Using the clay provided and build a model of the process of mitoses. The clay must represent the chromosomes. • Cut pieces of paper to represents the cell structures/stages. • Especially pay attention to the structure of the chromosomes.
Prophase 1 Metaphase 1 Anaphase 1: Two daughter cells Meiosis First meiotic division
Meiosis I Interphase: Duplication of each chromosome Prophase I: Paring of homologous Chromosomes - chiasmata – crossing over Metaphase I: Organisation of two tetrads in the equatorial plane Anaphase I: Separation ofhomologous chromosomes Completion of Meiotic division: Two daughter cells each with two dyads
Crossing over Significance of crossing over: Genetic material is exchanged – cause variation
Second meiotic division Metaphase II Anaphase II Four haploid cells, each with two chromosomes known as reproductive cells. (ovum or sperm)
Second meiotic division Metaphase II: Each daughter cell from the previous division has two dyads Anaphase II:–Mitotic separation of chromatids of each chromosome Completion of second meiotic division – four haploid cells, each with two chromosomes known as reproductive cells. (ovum or sperm)
Sex cells Sperm and Ovum
Activity 3 (LO1) Each group use the clay and build the process of meiosis
The importance of Meiosis: • The process of meiosis reduces the number of • chromosomes by half • One cell divides into four cells with each the haploid (n) • number of chromosomes • The first meiotic division reduces the number of chromosomes • The second meiotic division is actually mitosis which • increases the number of cells • Meiosis is the process through which gametes are prepared for • fertilisation. • Meiosis ensures that the number of chromosomes in the species stays the same over generations • Meiosis is important to introduce genetic variation.