Nucleic Acid Structure: Food Science

• The session focuses on Nucleic Acid Structure, as part of a Level 6 Certificate in Food Science and Technology.
• DNA is the hereditary material responsible for species and individual characteristics and can be passed to the next generation, enabling cells to produce identical daughter cells.
• DNA is organized into chromosomes, found in the nucleus (or nucleoid in bacteria), and packaged with histone proteins.
• Genes, found within DNA, contain instructions for making specific proteins.
• The nuclear envelope/membrane separates the nucleus from the cytosol, featuring two lipid bilayers, with nuclear pores allowing substance passage.
• Nucleoplasm fills the space inside the nucleus like a gel-like substance resembling cytosol.

Nucleic Acid Types

• DNA stores and transmits hereditary information.
• RNA is derived from DNA and is used in protein synthesis.
• Genes are segments of DNA organized into chromosomes, with each gene containing information to make a specific protein.
• mRNA is a messenger RNA and is used for protein synthesis via transcription.
• mRNA copies genes, carrying the genetic information to make proteins.
• tRNA(transfer RNA) carries amino acids to ribosomes for translation, acting as a link between mRNA and the growing amino acid chain.
• Transcription makes RNA copies of genes.
• Translation synthesizes proteins for cellular functions.

Nucleotide Composition

• DNA and RNA are made from nucleotides, which have two types: purines and pyrimidines.
• Purines contain a double-ring nitrogen base, including adenine (A) and guanine (G).
• Pyrimidines contain a single-ring nitrogen base, including cytosine (C) only in DNA, thymine (T) only in DNA, and uracil (U) only in RNA.
• Nucleotides consist of a phosphate group, a pentose (5-carbon) sugar, and a nitrogenous base.
• DNA contains deoxyribose sugar.
• RNA contains ribose sugar.

DNA vs RNA

• DNA has deoxyribose sugar while RNA has ribose sugar.
• DNA contains the bases adenine, guanine, cytosine, and thymine.
• RNA contains the bases adenine, guanine, cytosine, and uracil.
• DNA stores genetic information in the nucleus.
• RNA transfers genetic information to the cytoplasm for protein synthesis.
• DNA is typically a double-stranded molecule.
• RNA is typically a single-stranded molecule.

DNA Structure

• DNA is a double nucleotide chain with hydrogen bonds between opposing nucleotide base pairs.
• The double strand forms a double helix structure in 1953, discovered by James Watson & Francis Crick.
• In a double helix, the two strands face in opposite directions, with the 5' end of one strand paired with the 3' end of the other.
• Pyrimidines form hydrogen bonds with purines only. Adenine (A) bonds with Thymine (T), and Guanine (G) bonds with Cytosine (C).
• Bonding depends on the size of the ring structure associated with the base.
• Guanine and adenine bases have a purine ring structure (2 rings).
• Cytosine and thymine bases have a pyrimidine ring structure (1 ring).
• A purine pair would be too close and bulky in the helix structure.
• Adenine pairs with Thymine via two hydrogen bonds.
• Guanine pairs with Cytosine via three hydrogen bonds.

Chromosomes and Histones

• The haploid human genome includes approximately 3 billion base pairs of DNA, packaged into 23 chromosomes.
• Most cells are diploid, and contain 23 pairs of chromosomes, for a total of 6 billion base pairs of DNA per cell.
• Histones compact chromosomal DNA, forming chromatin.
• Histones are small and positively charged proteins.
• DNA is negatively charged due to phosphate groups.
• Histones bind with DNA tightly.
• The first level of packing is the nucleosome.
• Each nucleosome contains eight histone proteins and DNA wraps around the histone to achieve a condensed coiled form.
• Chromatin folds to form chromosomes, each containing one double-stranded DNA piece and histones.
• During cell division, chromatin becomes tightly packed.
• During interphase the chromatin is loosely packed.
• The looser configuration permits DNA replication and transcription.
• Prokaryotic DNA is in a single circular chromosome in the cytoplasm and prokaryoticcells lack a nucleus.

DNA Replication and Mutations

• DNA replication is semi-conservative, meaning that the resulting double helix is composed of one old and one new strand.
• A genetic mutation is a change in the DNA sequence, potentially leading to incomplete or damaged DNA, genetic disorders, or illnesses.
• Mutations can result from changes in the order of base nucleotides, where: ATA encodes Methionine and GTA encodes Valine.
• Gene mutations can be caused by changes in one or more nucleotides, changes in many/loss of one or more genes, and rearrangement of genes/chromosomes.
• Genetic mutations, such as cystic fibrosis, hemophilia, sickle cell anemia and Huntington's diseases, can be passed on if present in a parent’s egg or sperm.
• Other mutations, such as skin cancer, can occur during a person's life.

DNA Separation Analysis

• DNA has a strong negative charge due to phosphate groups.
• The DNA/RNA migrates towards the positive electrode when placed into a porous gel containing buffer, upon application of an electric current.
• Smaller DNA/RNA molecules move fastest through the gel.
• This DNA analysis technique is called agarose gel electrophoresis.
• The agarose gel electrophoresis method involves pouring an agarose and buffer solution into a plastic tray, allowing it to polymerize into a gel, and removing a comb to form wells for samples.
• DNA samples colored with a tracking dye are pipetted into the wells and placed into a chamber that generates an electric current through the gel.
• The gel has a negative electrode near the samples and a positive electrode on the other side.
• DNA molecules, having a negative charge, are drawn toward the positive electrode, with smaller molecules traveling faster.
• One well contains a DNA ladder with fragments of known sizes.
• A fluorescent stain visualizes the DNA bands following separation.
• Upon UV illumination, the stain binds to the DNA, the DNA bands appear as fluorescent.
• Ethidium bromide is extremely carcinogenic, although SybrSafe is a safer option.
• By comparing samples to the known ladder the DNA sample sizes can be determined.

Conclusion

• DNA functions to allow/pack densely.
• There are two RNA types.
• DNA carries hereditary material and results in for gene expression.
• Gene mutations can occur during replication, which may result in disease or illness.
• Through gel electrophoresis, DNA can be separated by size and charge.

Key concepts from the video, in question form

• How is DNA organised and what are the steps or stages?
• What are the structures of nucleotides and what role does bonding have in forming DNA?
• What are some examples of genetic mutations?
• How is DNA separated in DNA Separation Analysis?

Explore Nucleic Acid Structure, focusing on DNA and RNA within the context of a Level 6 Certificate in Food Science and Technology. Learn about DNA's role in heredity, its organization into chromosomes, and the function of genes in protein synthesis. Also, understand the structure of the nucleus, including the nuclear envelope and nucleoplasm.