12 Biology 4.1 DNA

Nucleotide

Composed of a nitrogenous base (adenine, thymine, cytosine, guanine), a sugar (deoxyribose in DNA, ribose in RNA) and a phosphate group.

Deoxyribonucleic acid (DNA)

Double helix structure resembling a twisted ladder

Ribonucleic acid (RNA)

Single stranded

Histones

Are small protein molecules essential for the coiling and supercoiling of DNA in chromatin.

Nucleosome

Is the basic structural unit of chromatin, consisting of a segment of DNA wound around a histone octamer.

Chromatin

Consists of DNA wrapped around DNA proteins, forming nucleosomes.

Chromatin =

DNA + all the proteins associated with it (mainly histones)

DNA in Prokaryotes

Unbound circular DNA in the cytosol, known as the genophore. Small rings of DNA called plasmids may also be present (additional DNA).

Exons

Any part of the gene that will code for a protein=

Introns

Non coding regions of DNA

Centromeres

The region of a chromosome where the two sister chromatids are joined.

• It plays a role in chromosome segregation during cell division.

Telomeres

Repetitive DNA sequences at the ends of chromosomes that protect them from dehydration and fusion with other chromosomes.

Interphase

The cell grows larger.

The cell produces more organelles and proteins it will need for division.

The DNA is copied so each chromosome now has two identical chromatids.

The DNA is spread out as loose chromatin in the nucleus, so individual chromosomes cannot yet be seen.

Anaphase 1

The chromatin coils tightly and becomes visible as chromosomes.

The nuclear membrane and nucleolus break down.

Homologous chromosomes (one from each parent) pair up.

Non-sister chromatids may exchange sections of DNA. This process is called crossing over and increases genetic variation.

Crossing Over

The process in Prophase 1, where homologous chromosomes pair up closely to form bivalents.

Alleles

Different variations of the same gene located on a chromosome.

Insertions

During meiosis, a piece of one chromosome can detach and then join onto its matching homologous chromosome. This causes an insertion mutation, in which additional genetic material becomes added into the chromosomes.

Deletions

During meiosis, part of a chromosome can break away and be lost. This produces a deletion, meaning some geentic material is absent from the chromosome.

Duplication

Sometimes during meiosis, a section of a chromosome can be copied twice, resulting in duplication where an extra copy of that chromosome segment is present.

Inversions

An inversion happens when a section of a chromosome breaks away, reverses its orientation, and then rejoins the same chromosome.This changes the order of genetic material within chromosome.

Translocations

A translocation occurs when sections of DNA are swapped between chromosomes that are not homologous.This can move genetic material from one chormosmoe to another and may interfere with normal gene function.

Aneuploidy

Is the condition in which a cell has an unusual number of chromosomes, usually caused by non-disjunction.Occurs when chromosomes fail to split during meiosis 1 and 2 and in mitosis.

Ploidy

is the usual amount of chromosomes (46).

Diploid

Means it has 46 chromosomes.

Haploid

Has only one set of chromosomes (23).

Spermatogenesis

The process of male gamete formation, where diploid stem cells in the testes undergo meiosis and differentiation to produce four functional, motile haploid sperm cells (n). This process occurs continuously from puberty throughout life.

Oogenesis

The process of female gamete formation, where diploid stem cells in the ovaries undergo meiosis to produce a single functional haploid egg cell (ovum) and three non-functional polar bodies. This process begins before birth, pauses, and is completed only after fertilization.

Process of making recombinant DNA

1. Isolation

2. Prepare the plasmid

3. Glue in the DNA

4. Bacteria transformation

5. Produce the protein

Recombinant DNA Step 1 - Isolation

A restriction enzyme identifies a specifici DNA base sequence and cuts the DNA at that exact site. If two DNA fragments have complementary sticky ends, they can join together easily.

Restriction Enzymes:

Restriction enzymes (or DNA scissors) cut DNA at specific recognition sites. Scientists use restriction enzymes to cut out a gene (e.g. human insulin).

Recombinant DNA Step 2 - Prepare the Plasmid

The same restriction enzyme used to cut out the DNA fragment in step 1 is used to cut the plasmid once.

• The recombinant plasmid is then placed back into a backterium.

Plasmids

Contain extra DNA and extra coding along with bacterial DNA.

• Scientists use plasmids as tools to transfer genes between organisms.

• Plasmids are used as vectors - vehicles to deliver genetic material into cells.

Recombinant DNA Step 3 - Glue in the DNA

DNA ligase joins the gaps in the DNA backbone.

• In recombinant DNA, it connects the DNA fragments to the plasmid, forming a recombinant plasmid that contains the gene.

Recombinant DNA Step 4 - Bacteria Transformation

Plasmids can be inserted into bacteria through a process called transformation.

• Specially prepared bacterial cells are exposed to a heat shock, which helps them absorb foriegn DNA.

Recombinant DNA Step 5 - Produce a Protein

Once a bacterial colony containing the correct plasmid is identified, it can be grown into a culture.

PCR Uses:

Enables us to extract a small amoutn of DNA from a single hair or drop of blood at the scene of a crime and amplify it so there is enough that it can be analysed.

PCR Purpose

PCR purpose: to take a very small sample of DNA and amplify it (make lots of copies) to a large enough amount to study in detail.

Gel electrophoresis purpose

To seperate DNA fragents based on size

Gel electrophoresis uses

Determine paternity or criminals: DNA profiling

Gel electrophoresis in DNA profiling.

DNA profiling uses gel electrophoresis to create a visible pattern of DNA bands, then compares that pattern between samples.

Evolution

Evolution refers to changes in the genetic makeup of a population across many generations, which may eventually result in the formation of a new species.

Microeveolution

• Refers to small scale changes in allele frequencies within a species or population.

• These changes occur over relatively short periods of time andd o not result in the formation of a new species.

• The descendants remain within the same taxonomic group as their ancestors.

Macroevolution

• Involves large scale changes in allele frequencies that occur at or above the species level over geological time.

• This process results in thed viergenceof taxonomic groups, leading to the formaiton of new species.

• The descendants in macroevolution are in different taxonomic grup compared to their ancestors.

Drivers of Evolution

The drivers of evolution include:

• sexual reproduction

• mutation

• genetic drift

• gene flow

• natural selection

These occur with an accumulation of microevolutionary changes leading to macroevolution.