Unit 4

DNA and Heredity

• The unit explores genetics.
• The global context is identities and relationships.
• The key concept is relationships, with evidence, models, and patterns as related concepts.
• Statement of Inquiry: Genetic factors determine identity and relationships.
• Scientific evidence has led to models that help to understand observed inheritance patterns.
• Inquiry Questions:
• What evidence proves the relationship between species’ genome and identity?
• How are inheritance patterns justified by the model of DNA?
• Should humans base moral reasoning and ethical judgment on phenotypical differences?

Genome – Chromosomes and genes

• Deoxyribonucleic acid (DNA) is a molecule essential to all life on Earth.
• DNA contains the code that determines the shape and structure of living things.
• Offspring inherit characteristics from their parents through DNA.

DNA structure

• DNA is a macromolecule with a double helix structure composed of two strands.
• Each strand consists of nucleotide units.
• Nucleotides are made of a phosphate, a sugar, and a base.
• The four bases are: adenine (A), cytosine (C), thymine (T), and guanine (G).
• A phosphate and sugar join with other nucleotides to form long chains.
• The chains are joined in a double helix with the bases.
• Adenosine (A) always pairs with thymine (T), and guanine (G) always pairs with cytosine (C), this is called complementary base pairing.
• The sugar and phosphates form the backbone of DNA.
• The bases determine the genetic code, which is the set of rules that translates DNA or RNA sequences into amino acid sequences.
• The genetic code determines the characteristics of an organism.

Chromosomes

• DNA is divided into individual lengths called chromosomes.
• Chromosomes are small bodies in the nucleus that carry the chemical instructions for cell reproduction.
• They consist of DNA strands wrapped around a core of proteins.

Diploid vs. Haploid Cells

• A diploid cell has a nucleus containing two sets of each chromosome and is nearly all body cells, or somatic cell.
• A haploid cell contains only a single set of unpaired chromosomes and is sex cells, sperm, and egg, or gametes.

Karyotype

• The number of chromosomes is a characteristic feature of species called the karyotype.
• Humans have 46 chromosomes, or 23 pairs of chromosomes.
• The twenty-third pair determines sex, with XX for females and XY for males.
• There are two types of sex chromosomes: a larger X and a smaller Y.
• If two X chromosomes are present, a baby develops as a female.
• If one X and one Y chromosomes are present, the baby will develop as a male.

Genes and Alleles

• Genes are lengths of genetic code on chromosomes that determine different characteristics.
• A gene is a heritable factor of DNA that influences a specific characteristic.
• Every gene occupies a specific position on a chromosome.
• Bacteria have fewer genes than eukaryotes.
• Some animals have fewer genes than humans, but some have more
• Plants may seem less complex than humans, but some have more genes.
• A gene consists of a sequence of 3 bases (a codon) and codes for a protein molecule.
• Alleles are variant forms of a gene with slight differences in their base sequence.
• Alleles influence the same characteristic, occupy the same position on a chromosome, and have slightly different base sequences.

Example Allele

• The human gene for the protein of haemoglobin is adenine (A) in the most common allele of the gene.
• There is a less common allele which has a thymine (T).
• This allele causes the genetic disease called sickle cell anaemia (type of blood disorder).
• Homologous chromosomes are chromosomes of one particular type.
• Homologous chromosomes have the same genes in the same sequence/place.
• They may not have the same alleles of those genes.

Genome Information

• The genome is the complete genetic information of an organism.
• The size of a genome is the total amount of DNA in one set of chromosomes, measured in millions of base pairs (bp).
• Genome sizes can vary significantly.
• Examples of Genome Sizes:
• T2 phage: 0.18 million base pairs
• E. coli: 5 million base pairs
• D. melanogaster: 140 million base pairs
• Homo sapiens: 3,000 million base pairs
• P. japonica: 150,000 million base pairs

Cell Division

• In eukaryotes, most DNA is stored in the nucleus.
• A human nucleus has 2 meters of DNA but is only 5 µm in diameter.
• DNA fits by attaching to proteins that coil genetic information into chromosomes.
• This process is called DNA condensation.
• Uncoiling of DNA is necessary for DNA replication, mitosis, and meiosis.

DNA Replication

• The uncoiling of chromosomes allows the 'unzipping' of the double helix structure.
• This unzipping allows for genetic information to be read and replicated.
• Is an essential step before cell division.
• Mitosis:
• Both uncoiling and condensation are vital steps in the several stages of cell duplication.
• Meiosis: Both the uncoiling and condensation are vital steps in the several stages of production of sexual cells, also called gametes.

DNA Replication Mechanism

• Semi-conservative replication is a method of copying DNA.
• The two DNA strands are separated by breaking the hydrogen bonds between their bases.
• New nucleotide polymers assemble on each single strand.
• A template strand is a strand of DNA on which a new strand is assembled.
• Due to complementary base pairing, new strands have the same sequence as the old strand.
• The result is two identical DNA molecules, each with one new and one conserved strand, making replication semi-conservative.
• DNA replication creates two identical copies of a DNA molecule.
• This is essential for cell division during growth or repair of damaged tissues.

Simplified DNA Replication Steps

• Helicase unwinds the double helix and separates the two strands.
• DNA polymerase attaches to the old strand and uses it as a template.
• Once DNA polymerase detaches, so does the new DNA strand.
• Helicase is released and the old double-helix is closed.

Mitosis and Cell Division

• Mitosis leads to two genetically identical daughter cells, during cell duplication or reproduction.
• Note: DNA replication is not mitosis, but mitosis separates newly replicated chromosomes.
• Before cell division, each chromosome copies itself into strands through DNA replication during interphase.
• Each strand becomes a chromatid.
• Chromatids are held together by a centromere and are called sister chromatids.
• During mitosis, each double-stranded chromosome becomes single-stranded again.
• One copy of each chromosome is then in a new cell.

Mitosis Stages

• Mitosis has four stages:
• Prophase:
• Chromosomes condense for movement.
• Chromosomes become distinct threads.
• The nuclear membrane breaks down.
• Metaphase:
• Chromosomes line up in the cell's center (equator).
• Spindle fibers move chromosomes into place.
• Anaphase:
• Spindle fibers contract and separate chromatids.
• Chromatids are pulled to opposite ends of the cell.
• Telophase:
• The nuclear membrane reforms.
• Chromosomes unwind for function.
• Cytokinesis follows mitosis the cytoplasm divides, creating two cells.
• Mitosis results in two genetically identical diploid cells from one cell.

Cell Cycle

• The cell cycle is an ordered set of events culminating in cell division.
• The cell cycle has phases:

First growth phase (G1)

• The cell grows to prepare for DNA replication.
• ensuring that all its chromosomal content can fit inside itself. . TheCell is diploid
• Synthesis phase (S): The cell undergoes DNA duplication,
• doubling its chromosome number. at 4n -Example, human cells ends up with chromosomes/92 chromosomes.
• Second growth phase (G2):Cell grows, makes sure gets doubled.Cell is still a tetraploid
• Mitosis: Nuclear division
• cell The nucleus divided into 2x 2n.
• Cytokinesis: Cytoplasmic division, so segregation and division occur.2x 2individual diploid cells

Meiosis – Haploid cells

• Meiosis creates sex cells with reduces chromosomes.sperm/eggs.created in the testes.
• The number of chromosomes are halved to create sex cellslies and testes.All formed egg cells have a chromosome X.
• In meiosis, a diploid nucleus divides twice.chromosomes consists of chromatids.separation of pairs of homologous creates chromosome number in DNA
• In summary:From(4n)-> two (2n).

What you need to know: Meiosis

• Meiosis includes these steps: prophase I, metaphase I, anaphase I, telophase I, prophase II, metaphase II, anaphase II, and telophase II.
• The process results in genetically varied haploid cells for genetic variation.

Manufacture of Proteins Through RNA

• DNA remains in the nucleus.
• The information is stranded in the core of cells.
• The information to manufacture outside its borders at the ribosome.Overcome using the cell’s dogma.

Key concepts

• A three strand base is a DNA that codes the specifics molecules to allow it to be able to translate at the ribosome.RNA copies allowing biology’s dogma.
• RNA is a small molecules that a molecule of DNA where only one strand exists compared to the other counterpart.Role.
• RNA is responsible translation for copying transferring the data sequence into smaller RNA, RNA has to decode,read, and transport to create synthesis of proteins.reading RNA allows all process.

DNA codes Summary

1. In the nucleus, DNA has expose its bases translation- a RNA polymer-copy the strand in bases
2. the process happens by the release of cytosol by ribosomes.Ribosomes have a function determine codes to get translation.

RNA and DNA

• Note the there a differences in nucleotides of both DNA with RNA

1. 2 bases of same are identical- and the bases consist of 3 bases- adenine and the rest is the same.DNA fourth bases is is different in a way
2. Sugars is different in the ribose for RNA and deoxyribose for DNA

Protein Synthesis

Genetic code comes from mRNA is responsible making sequences genetic codes triplets of 3bases- code to singlets of amino acids

Group base

• If there 4 bases assuming to 3- the codes can reach up to a max of 64 combinations.
• Amino acids- linked by reactions of proteins that allows short chains which known called as peptides.The 1 base of amino acids are all connects allowing sequences of bonds called as protein bonds

More Information

• -Chains with more than 40 peptides- di chains consist of two amino acids that has protein links.Polypeptide acids has bonds more to unbranches.Proteins consist both poly’s singles/multiples.

Mutation Information- Random sequence

• Random process leads to changes both with genes, the change allow not leads to characteristics through the physical of change
• can be pass on and its both can harmless in damaged

Mutations - Why its Important

• Source of genetic traits and very few is good some is cancerous.

Types of Change

• Point Change

1. normal
2. insertion change
3. deletion changes.
4. duplication
5. inversion change

Damage for Mutations and Mutagens

• Mutagens- leads to alteration both through physical and the substance that consists mutation, that be induced at 2types.Energy/chemical induced.

High-energy radiation

• radiation -nuclear accident -Chernobyl and radiation in Hiroshima

Chemical- induced by solvents.

A Point Mutation

• Change through 1 based- causes of change from the result as addition and deletion.all effects need to be a part of replication and the replication needs to always occur under the division

The cycle of inheritance.

• Inherited traits are genetic traits from a generations passes with the connection it holds, during reproduction of sperm/egg-it’s to parents the organisms has data, making it.
• A clone