Nutritional Biochemistry Genetics Quiz

Nutritional Biochemistry - Introduction to Genetics

• Course code: DIET413/BHCS1019
• Lecturer: Dr Nathaniel Clark
• Email: [email protected]

Questions

• Question 1: Proteins spanning the membrane with alpha helices contain amino acid side chains central to the complex
• Question 2: Transport proteins moving solutes against a concentration gradient are carrier proteins, not channel proteins, because they bind to solutes and change shape to move them.
• Question 3: Simple diffusion moves substances with their concentration gradient, while facilitated diffusion uses transport proteins.
• Question 4: Active transport uses chemical or electrical energy.
• Question 5: Na+ and K+ channels have similar structures but different orientations, allowing Na+ to enter the cell and K+ to exit.

Learning Outcomes

• Describe DNA structure and organization in the nucleus
• Describe DNA replication
• Outline the transcription and translation of a gene into a protein
• Briefly outline the structure, control, and role of mtDNA, and associated diseases

Genes and Genetics

• Humans have 100 trillion cells, each nucleus containing 46 chromosomes (23 pairs).
• Genes are DNA sections that code for protein synthesis.
• Each chromosome pair receives one chromosome from each parent.

The Genome

• Every cell in an organism has the same genetic information.
• The genome controls the biochemical activity in response to various stimuli.
• The inherited traits are transmitted from generation to generation.
• The human genome contains approximately 20,000-21,000 genes.
• 99.9% of human genes are similar across individuals.

The Structure of DNA

• The genome is made up of DNA.
• DNA is a long chain of nucleotides.
• DNA is a double helix, analogous to a ladder.
• DNA is 2nm wide and has 10.5 steps per turn (3.4 nm).

DNA Methylation

• DNA methylation involves adding a methyl group to DNA.
• Demethylation is the removal of a methyl group.

Nucleosides

• Nucleosides consist of a sugar and a nitrogenous base.
• The base is attached to the sugar via a bond.

Nucleotide Structure

• Nucleotides comprise three parts: a sugar, a base, and a phosphate group.
• Nucleotides, connected by phosphodiester bonds, form the phosphate-sugar backbone.
• Sugars are 5-carbon pentose sugars.

Hydrogen Bonding Between Bases

• DNA bases only bond with specific bases:
  • Adenine with Thymine
  • Guanine with Cytosine
• Complementary base pairing is fundamental for DNA replication and translation.

Polynucleotides

• Nucleotides form polynucleotides, which are the fundamental structural units of DNA.
• Phosphodiester bonds link nucleotides, creating the phosphate-sugar backbone.

The DNA Double Helix

• The deoxyribose chains and base-sugar bonding create a DNA double helix structure.
• The DNA strands run antiparallel (3' and 5').
• Directionality of the DNA strands is critical for DNA processes.

Histones, Chromatin, and Chromosomes

• DNA packaging for storage involves histones, forming nucleosomes.
• Nucleosomes condense into chromatin fibers.
• Chromatin fibers condense into chromosomes.

Structure of Genes

• A gene is a specific segment of DNA that encodes the amino acid sequence for a protein.
• Genes are the fundamental units of inheritance.
• Chromosomes have genes located in bands along their structure.

Telomeres

• Chromosomes have protective caps called telomeres.
• Telomeres prevent degradation and fusion of chromosomes.

The Cell Cycle

• DNA replication is part of the cell cycle.
• The cycle includes G1, S, and G2 phases, with G0 as a resting phase.
• G1: Cytoplasm and organelles increase.
• S: DNA is precisely duplicated.
• G2: Cell and organelle growth.
• M: Mitosis and cell division occur.

Cell Cycle Checkpoints

• Checkpoints ensure accuracy in replication and division.
• 3 checkpoints:
  • G1 checkpoint.
  • S checkpoint.
  • M checkpoint.

DNA Replication

• Copying DNA to generate identical copies for daughter cells during cell division.
• Replication occurs by unwinding the DNA double helix and synthesizing complementary strands on each parent strand.

Replication Fork

• The region where the DNA unwinds is known as the replication fork.
• Replication takes place in the 5' to 3' direction.

Leading/Lagging Strands

• Leading strand: synthesised in a continuous manner following the replication fork.
• Lagging strand: synthesised discontinuously in segments called Okazaki fragments.

DNA Replication - Lagging Strand

• RNA primer initiates synthesis steps.
• DNA polymerase replaces RNA primer with DNA.
• Okazaki fragments are joined together.

Mitochondria DNA (mtDNA)

• Mitochondria produce energy (ATP) via oxidative phosphorylation.
• mtDNA is a small, circular, double stranded
• mtDNA controls some mitochondrial functions.
• mtDNA is only found in animal cells, maternally inherited.

mtDNA Replication

• The replication method of mtDNA is controversial.
• Two theories exist for mtDNA lagging strand timing.

mtDNA Transcription & Replication - Differences

• mtDNA lacks introns and non-coding sequences.
• Termination codons are post-transcriptionally created.

Mitochondrial Disease

• Mitochondrial dysfunction is linked to aging and degenerative diseases.
• mtDNA is susceptible to damage from free radicals.
• Certain disorders are caused by mutations in mtDNA.

Energy Failure Through Damage

• Cells lacking sufficient aerobic ATP production may resort to anaerobic respiration (using lactate).
• Reduced ATP generation often results in cellular acidosis.
• This is often observed in tissues with high metabolic demands, such as the CNS, heart, and skeletal muscle.

Mitochondrial DNA Mutations

• Parkinson's disease (PD) is one disorder in which mtDNA mutations have been identified.
• mtDNA mutations may result from reactive oxygen species (ROS), affecting ATP production in dopaminergic neurons.
• Cancer may be related to mtDNA mutations, but the relationship isn't fully understood yet.

From Genes to Proteins

• DNA carries the instructions to make proteins.
• Transcription and translation are critical steps.
• Proteins perform numerous cellular functions.

Transcription

• DNA acts as a template, creating an mRNA message.
• The process is called transcription.
• mRNA carries the information to the ribosomes.

Initiation of Transcription – TFs

• General transcription factors bind to the promoter region of DNA to initiate transcription correctly.
• Transcription factors control the rate of transcription.
• Hormones and messengers bind to, and activate, transcription factors.

Initiation of Transcription – Other Regions

• Enhancers and the TATA box further fine-tune transcription initiation efficiency.
• The TATA box helps in locating RNA polymerase correctly.

Chain Initiation

• RNA polymerase begins attaching nucleotides to create an RNA molecule.
• This process begins at the transcription start site.

Chain Elongation

• RNA polymerase synthesizes RNA in the 5' to 3' direction, according to the DNA template.

Chain Termination

• Special DNA sequences cause RNA polymerase to detach from the DNA molecule.

Post-transcriptional Modification

• Introns are removed from the initial RNA transcript, keeping only the exons coding for proteins.
• mRNA splicing removes non-coding sequences.

Translation

• Amino acids are linked according to the mRNA codon sequence.
• Ribosomes and transfer RNA (tRNA) facilitate amino acid attachment.

Ribosomes

• The site of protein synthesis.
• Ribosomes are large RNA-protein complexes (rRNA + protein).
• Ribosomes have 2 subunits, A and P sites, for amino acid binding and peptide bond formation.

Transfer RNA (tRNA)

• tRNA molecules carry amino acids to the ribosomes, based on the mRNA instructions.
• tRNA contains an anticodon sequence.
• Anticodon sequences are complementary to mRNA codons.

The Triplet Code

• Three bases (a codon) specify each amino acid.
• The genetic code describes how codons relate to amino acids.

Elongation of Peptide Chain

• Subsequent amino acids are joined based on mRNA codons to extend the growing polypeptide chain.

Termination of Translation

• Termination of protein synthesis occurs after reaching specific stop codons.
• Ribosomal subunits separate, releasing the polypeptide chain.