Comprehensive Biology Review Flashcards

Foundational biology flashcards based on lecture notes covering biochemistry, cell biology, genetics, metabolism, and ecology.

How is a glycosidic bond formed between two monosaccharides?

It is formed via a condensation reaction involving an enzyme, with the loss of one $H_2O$ molecule.

What are the structural components of Starch?

Starch is a polymer of $\alpha$-glucose consisting of Amylose ($\alpha$-1, 4 glycosidic bonds, unbranched helix) and Amylopectin ($\alpha$-1, 4 and $\alpha$-1, 6 glycosidic bonds at branch points, every 20-30 monomers).

Why is Cellulose structurally suitable as a plant cell wall component?

It consists of $\beta$-glucose joined by $\beta$-1, 4 glycosidic bonds where alternate molecules rotate $180^{\circ}$, forming long straight chains. Extensive inter-chain hydrogen bonding results in high tensile strength microfibrils that prevent osmotic bursting.

What is the structure and function of a Triglyceride?

It consists of one glycerol and three fatty acids joined by ester bonds via condensation. Its primary functions are long-term energy storage, thermal insulation, and protection against mechanical shock.

Describe the primary structure of a protein.

The primary structure is the unique number, sequence, and type of amino acids in a polypeptide chain, maintained by peptide bonds and determined by genes.

Compare the structure and function of Haemoglobin and Collagen.

Haemoglobin is a globular protein with a quaternary structure of four subunits ($2\alpha$, $2\beta$), each with a haem group containing $Fe^{2+}$ to transport $O_2$. Collagen is a fibrous protein consisting of a triple helix (tropocollagen) with glycine at every third position, providing high tensile strength to connective tissues.

What characterizes a Prokaryotic cell compared to a Eukaryotic cell?

Prokaryotic cells are small, unicellular, lack membrane-bound organelles, have $70S$ ribosomes, and contain circular DNA in a nucleoid region. Eukaryotic cells have membrane-bound organelles (e.g., nucleus, mitochondria), $80S$ ribosomes, and multiple linear chromosomes.

What is the function of the Golgi apparatus?

It consists of a stack of flattened membrane-bound sacs that modify, sort, and package molecules (e.g., glycosylation of proteins to glycoproteins) into vesicles for secretion or intracellular transport.

Explain the role of DNA Polymerase III in DNA replication.

It adds deoxyribonucleotides to the $3'$ hydroxyl ($\text{-OH}$) end of an existing chain by complementary base pairing and catalyses phosphodiester bond formation in the $5'$ to $3'$ direction.

Identify the three steps of post-transcriptional modification in eukaryotes.

1. $5'$ capping (7-methylguanosine cap); 2. $3'$ polyadenylation (Poly-A tail); 3. RNA splicing (removal of introns and joining of exons by spliceosomes).

What is the molecular basis of Sickle Cell Anaemia?

A non-conservative missense point mutation in the $\beta$-globin gene (typically $GAG$ to $GUG$ in mRNA) changes the 6th amino acid from hydrophilic glutamate to hydrophobic valine, causing HbS to polymerise into rigid rod-like fibers under low $O_2$ tension.

Differentiate between Allopatric and Sympatric speciation.

Allopatric speciation occurs when a population is geophysically isolated by a physical barrier (e.g., Isthmus of Panama). Sympatric speciation occurs within the same geographic area due to physiological or behavioral isolation (e.g., unique mating calls or flowering times).

What are the three main steps of the PCR cycle?

1. Denaturation (at $95^{\circ}C$ to break hydrogen bonds); 2. Primer Annealing (at $60^{\circ}C$ to allow primers to bind to target sequences); 3. Extension (at $72^{\circ}C$ where Taq Polymerase synthesises new DNA strands).

In the Lac operon, what happens when lactose is present but glucose is absent?

Allolactose (inducer) binds to the lac repressor, inactivating it so it cannot bind to the operator. Simultaneously, Low glucose leads to high cAMP, which binds to CAP. The active CAP-cAMP complex binds to the promoter, increasing RNA Polymerase affinity and resulting in high transcription of structural genes.

What is the Net yield of products from Glycolysis per molecule of glucose?

The net yield is $2$ Pyruvate, $2$ $NADH$, and $2$ $ATP$ (via substrate-level phosphorylation).

Describe the process of chemiosmosis in oxidative phosphorylation.

Energy from electrons moving through the ETC is used to pump $H^+$ from the matrix into the intermembrane space, generating a proton-motive force. Protons diffuse back into the matrix through ATP synthase, driving the phosphorylation of $ADP$ to $ATP$.

Name the four factors that can limit the rate of photosynthesis.

Light intensity, Temperature, Carbon dioxide concentration ($[CO_2]$), and Chlorophyll/Pigment concentration.

What are the properties of Stem Cells?

They are undifferentiated and unspecialized cells capable of self-renewal via mitosis and can differentiate into various specialized cell types upon receiving appropriate molecular signals.

Define Epistasis and provide one example of a phenotypic ratio.

Epistasis is a gene interaction where the phenotypic expression of a gene at one locus masks the expression of a gene at a second locus. An example is Recessive Epistasis, which results in a $9:3:4$ ratio (e.g., Labrador fur color).

Explain the difference between Antigenic Drift and Antigenic Shift in the Influenza virus.

Antigenic Drift involves minor point mutations in genes for surface glycoproteins ($HA$, $NA$) leading to gradual changes. Antigenic Shift is a major change resulting from the reassortment of RNA segments when two different subtypes infect the same cell, potentially causing a pandemic.

What is the life cycle of the Dengue virus vector Aedes aegypti?

It involves complete metamorphosis: Egg, Larva (4 instars), Pupa, and Adult.

Describe the cell signaling pathway of Glucagon.

Glucagon (first messenger) binds to a GPCR, activating a G-protein that stimulates adenylyl cyclase to convert $ATP$ to $cAMP$ (second messenger). $cAMP$ activates Protein Kinase A (PKA), triggering a phosphorylation cascade that leads to glycogenolysis.