Unit 3: DNA & Genetic Technologies Notes

Unit 3: DNA & Genetic Technologies

Organelles in Cells

  • Animal Cell

  • Plant Cell

  • Organelles to identify:

    • Smooth ER

    • Golgi Body

    • Cell membrane

    • Rough ER

    • Nucleus

    • Ribosome

    • Lysosome

    • Vacuole

    • Mitochondrion

    • Cytoplasm

    • Chloroplast

    • Cell Wall

Introduction to DNA

  • DNA is the blueprint for a living thing, containing the genetic information in cells.

  • Nearly every cell in an organism has the same genetic information.

  • In animal and plant cells, DNA is stored in the nucleus.

  • DNA (deoxyribonucleic acid) determines organ and part development, assembly order, and how they work together.

Key Terms

  • Cell: Smallest unit of living things.

  • Nucleus: Control center of the cell.

  • DNA: Deoxyribonucleic acid, encoding genetic information, composed of nucleotides linked in a chain.

  • Chromosome: Thread-like structures where DNA is tightly packaged.

  • Gene: Segment of DNA molecule with coded instructions, determining an organism's characteristics.

  • Allele: Alternative forms of a gene arising by mutation, found at the same place on a chromosome.

DNA Structure

  • DNA stands for deoxyribonucleic acid, a chemical substance in the nucleus of all living cells.

  • DNA controls all chemical changes in a cell.

  • DNA determines the type of cell produced (muscle, blood, bone, etc.).

  • DNA determines the type of organism produced (buttercup, giraffe, penguin, human, etc.).

Genome

  • Genetic information is carried by DNA, a polymer of nucleotides in a double helix.

  • DNA is found within chromosomes.

  • A gene is a DNA section that carries coding for a protein, containing instructions for an organism's characteristic.

Structure of DNA

  • DNA is a long-chain molecule made of repeating sub-units (monomers) called nucleotides.

  • DNA usually has two strands twisted into a double helix.

  • Each nucleotide includes:

    • A phosphate (PO43−)(PO_4^{3-}) group

    • A deoxyribose sugar

    • An organic base

Deoxyribose vs Ribose Sugars

  • Ribose is a five-carbon sugar.

  • Deoxyribose is similar but has one less oxygen atom.

Nitrogenous Bases

  • Four different nitrogenous bases in DNA:

    • Adenine (A)

    • Cytosine (C)

    • Guanine (G)

    • Thymine (T)

DNA: A Polynucleotide

  • DNA is a polymer of mononucleotides.

  • Mononucleotides join between the sugar of one nucleotide and the phosphate group of the next.

  • The sugar and phosphate units make up the “backbone” of the nucleic acid.

  • A base is attached to each sugar molecule.

DNA Base Pairing

  • DNA usually has a double strand of nucleotides pairing up to form a “ladder”, then twisted into a double helix.

  • Sugar-phosphate “backbones” are on the outside, held by hydrogen bonds between bases.

  • Hydrogen bonds are weak individually but strong collectively.

  • Bases always pair up:

    • Adenine (A) with Thymine (T)

    • Cytosine (C) with Guanine (G)

The Genetic Code

  • DNA bases make up the genetic code.

  • The Human Genome Project found approximately 3.3 billion base pairs in our genome.

  • Human genes vary in size from a few hundred bases to more than 2 million.

  • Chemical cross-links between DNA strands are formed by base pairs (A-T & C-G), known as complementary base pairing.

  • The sequence of base pairs in a gene provides the code for the cell to build a protein.

DNA Adaptation to Function

  • DNA is heredity material for passing genetic information from cell to cell.

  • The structure of DNA has advantages:

    • It is stable.

    • Two strands can separate for self-replication.

    • It is a large molecule that carries lots of information.

    • Base pairing prevents corruption from outside chemicals or physical forces.

Summary of Key Points

  • A person’s genome consists of a complete set of genes.

  • DNA contains the genetic code that controls protein production in living things.

  • DNA is a polymer consisting of millions of nucleotides.

  • A nucleotide consists of sugar, phosphate, and a nitrogenous base.

  • The four bases pair complimentary (A-T and C-G).

  • The order of nitrogenous bases (AGCT) creates variation.

Watson and Crick DNA Model

  • Sugar-phosphate backbone.

  • Base pairs (Cytosine, Guanine, Adenine, Thymine).

  • Hydrogen bonds.

DNA Structure Activity

  • Cut & Paste activity to learn about DNA Structure.

  • Key includes Adenine, Cytosine, Thymine, Guanine, Phosphate, Deoxyribose.

The Double Helix

  • Sugar-phosphate chain.

  • A and T are complimentary base pairs.

  • C and G are complimentary base pairs.

History of DNA Structure

Rosalind Franklin

  • British chemist.

  • Showed phosphates must lie on the outside of the molecule in the early 1950s.

  • Obtained images of DNA using x-ray crystallography, including photo 51.

  • Independently concluded that DNA must have a double helical structure.

  • Her manuscript was published in the same edition of Nature as Watson & Crick’s.

  • Died in 1958 from cancer; her contribution was acknowledged much later.

Maurice Wilkins

  • New Zealand-born physicist.

  • Introduced the idea to study DNA with x-ray crystallography.

  • Franklin’s colleague; relationship was poor.

  • Wilkins shared photo 51 with Watson & Crick, without Franklin’s knowledge or consent.

  • Awarded Nobel Prize, along with Watson & Crick, for his work on DNA in 1962.

James Watson & Francis Crick

  • American zoologist (Watson) and British physicist (Crick).

  • Put together several models of DNA, attempting to incorporate all available evidence.

  • Used Franklin’s data (without her knowledge/consent) to arrive at the correct structure.

  • Awarded Nobel Prize, along with Wilkins, for their work on DNA in 1962.

The Genetic Code – Brief History

  • In the mid-1800s, Gregor Mendel proved that traits were passed on from parent to child.

  • Our understanding of cell biology and genetics increased through the early 1900s, leading to the discovery of DNA structure in 1952.

  • Scientists were unsure how genes encoded in DNA become the proteins that give us our phenotype (observable trait).

Protein Synthesis: Transcription & Translation

  • The processes where the genes encoded in DNA become the proteins.

Proteins

  • Proteins are large, complex molecules made up of one or more polypeptides.

  • Polypeptides are long chain molecules made up of amino acids.

  • Each protein has a specific function, such as enzymes, structural components of cells, hormones, etc.

Messenger RNA (mRNA)

  • DNA contains genes that work as instructions for protein synthesis.

  • DNA cannot leave the nucleus; ribosomes responsible for protein synthesis are outside the nucleus.

  • Messenger RNA (mRNA) is created as a copy of the genetic code that can leave the nucleus; it is a single-strand nucleic acid.

  • mRNA is made from the DNA template during transcription.

  • The role of mRNA is to carry information from the DNA to the ribosomes, which will translate the genetic code to synthesize appropriate proteins.

DNA vs RNA

  • DNA is double-stranded, while RNA is usually single-stranded.

  • The “backbone” of DNA is made of deoxyribose sugars and phosphate groups, RNA is made of ribose sugars and phosphate groups.

  • Both contain four possible nucleobases; thymine (T) is only in DNA, uracil (U) is only in RNA.

  • Adenine (A) can pair with both thymine (T) & uracil (U). Uracil (U) replaces thymine (T) in RNA.

Key Terms

  • Amino Acid: A small molecule that joins with others to form proteins. Amino acids are the building blocks of proteins, which are the building blocks of cells.

  • Polypeptide: A continuous, unbranched chain of amino acids joined by peptide bonds. Proteins are made up of one or more polypeptides.

  • Protein: A large molecule made up of amino acids. Proteins form structures and perform functions in an organism. DNA contains instructions for building proteins.

  • RNA: Ribonucleic acid. A nucleic acid with similar structure to DNA, however, unlike DNA RNA is single stranded. An RNA molecule has a backbone made of alternating phosphate groups and the sugar ribose, rather than the deoxyribose found in DNA.

  • mRNA: Messenger RNA. A type of RNA molecule created from the DNA template during transcription. mRNA acts as a copy of the genetic code that can leave the nucleus and provides instructions to the ribosomes during translation.

Protein Synthesis – Overall Process

  • Since the DNA instructions must remain in the nucleus, an intermediate molecule, messenger RNA (mRNA), is created, carrying a transcribed copy of relevant instructions from the nucleus to ribosomes in the cytoplasm.

  • Ribosomes translate the message carried by mRNA into a cell product such as protein.

Transcription

  • Transcription is the first step in synthesising a protein from the information contained in a gene. It involves copying the gene’s DNA sequence to make an RNA molecule known as messenger RNA (mRNA).

  • This process occurs in the nucleus of the cell.

  • Transcription is performed by enzymes called RNA polymerases, which link nucleotides to form an RNA strand (using a DNA strand as a template).

Phase 1: Initiation

  • RNA polymerase binds to a sequence of DNA called the promoter, found near the beginning of a gene.

  • Each gene has its own promoter.

  • Once bound, RNA polymerase separates the DNA strands, providing the single-stranded template needed for transcription.

Phase 2: Elongation

  • One strand of DNA acts as a template for RNA polymerase.

  • As it