Signal Transduction and Apoptosis

Last lesson we learned about the different types of signalling molecules (plant and animal hormones, neurotransmitters, cytokines and phermones). Today we will learn what happens when these signalling molecules reach their target cells, causing a response in the cell. Lipophobic (hydrophilic) signalling molecules cannot pass through the cell membrane, so they rely on complementary protein receptors that are embedded in the cell membrane. Once the signalling molecule – or ligand – binds to the receptor protein, secondary messenger molecules are released inside the target cell. Learn more about the specifics of signal transduction here:

Signal transduction from the Penguin Prof Channel

Signal transduction from Mr Bozeman (simple animated diagrams with commentary)

In the video above, observe one of the consequences of signal transduction – apoptosis or programmed cell death.

Cellular Respiration – aerobic and anaerobic


Cellular respiration is necessary to provide energy for cellular processes – repair and maintenance of cells, growth and cell division, active transport of substances across cell membranes and preventing disease.

Designing a scientific investigation poster

Pretty great poster for Grade 4 students!

Student Investigations in Biology

Unit 4: Area of Study 3 in the VCE Biology Study Design provides details of the practical investigation that students are required to complete, worth one third of the school assessed coursework for Semester 2.

On the completion of this unit the student should be able to design and undertake a practical investigation related to cellular processes and/or biological change and continuity over time, and present methodologies, findings and conclusions in a scientific poster.

There are a great number of practical investigations suitable for students, however, careful consideration of the materials and equipment available and the time taken to achieve useful results is prudent. The following resources provide lists of practical investigations that may be of interest:

When you have decided which investigation you are interested in and after discussion with your teacher, submit a proposal that includes the following information:

  • Your name
  • Title (up to ten words about the experiment)
  • Hypothesis (what exactly are you testing?)
  • Materials required (consumables)
  • Equipment required (experimental tools, glassware etc)
  • Estimated time for conducting the experiment and collecting results
  • References (Where did you get the idea from and what other information do you need?)

Week 6: Energy transformations in cells – photosynthesis

Learning intention: Students will understand the energy transformations from sunlight to chemical energy in the process of photosynthesis.

Watch the following videos and take Cornell notes. Especially pay attention to the products and reactants of the light-dependent and light-independent (Calvin cycle) parts of the reaction.

Week 5: Enzyme regulation in biochemical pathways

Image result for effect of pH on enzyme activity

Learning Intention: Students will better understand the use of mass spectroscopy in the diagnosis of a medical condition and explore the implications of enzyme deficiencies in protein metabolism. They will also understand the effect of pH on enzyme activity and apply their knowledge of scientific method to writing the procedure for a practical experiment.

Success criteria: Students will complete the practical activity “Absent enzymes – phenyketonuria and albinism”.

  • Liver contains an enzyme that catalyses the reaction to breakdown hydrogen peroxide (H2O2)
  • Enzyme activity in this case  is indicated by the production of oxygen – a splint re-ignites in the presence of oxygen.
  • High temperatures denature proteins and prevent enzyme activity.
  • Diastase in an enzyme in plants that converts starch into glucose at an optimum temperature of 20 degrees Celcius.
  • The presence of starch in solution is indicated by iodine turning blue-black.

Your task is to devise an experiment that demonstrates the effect of pH on enzyme activity. Remember that pH is a logarithmic scale – a pH of 4 is ten times more H+ ions than a pH of 5.
pH and Enzymes
Effect of pH on enzyme activity

Second-hand data activity: PKU Genetics (YouTube, 5.00min)

Week 4: Gene structure and regulation

Learning Intention: Students will understand the genetic code as a degenerate triplet code and the steps in gene expression including transcription, RNA processing in eukaryotic cells and translation. Students will also understand gene structure and regulation, especially start/stop, promoter regions, exons/introns and the lac operon.

Transcription – the process by which the DNA code is transcribed into messenger RNA in the nucleus of a cell. (DNA to mRNA)
RNA processing – the process by which introns are removed and the exons are spliced together, leaving a single-stranded mRNA molecule which travels through the nuclear pores into the cytoplasm.
Translation – the process by which the mRNA code is converted to a protein code by ribosomes adding amino acids that are attached to an anticodon that pairs with codons on the mRNA strand.
Gene structure and regulation
• the functional distinction between structural genes and regulatory genes
• the structure of genes in eukaryotic cells including stop and start instructions, promoter regions, exons and introns
• use of the lac operon as a simple prokaryotic model that illustrates the switching off and on of genes by proteins (transcriptional factors) expressed by regulatory genes.

Non-coding DNA explained
DNA transcription promoter
Gene expression and order of the operon
Lac operon from Virtual Cell

Week 3: Structure and function of nucleic acids and proteins

Image result for transcription and translation diagram

Learning Intention: To understand nucleic acids as information molecules that encode instructions for the synthesis of proteins in cells and the processes of transcription and translation in cells. Students will also understand protein functional diversity and the nature of the proteome as well as the functional importance of the four hierarchal levels of protein structure. They will perform experiments that demonstrate the effect of temperature and pH on enzymes.

  • Catalase is an enzyme found in liver extract that breaks down hydrogen peroxide (H2O2) into water and oxygen.
  • Hydrogen peroxide is a toxic product of digestion that needs to be eliminated from the body. Water and oxygen are the safe products of hydrogen peroxide breakdown.
  • Primary structure of protein – order of amino acids
  • Secondary structure – alpha helix, beta pleated sheets or random coils
  • Tertiary structure – folding of the polypeptide chain due to disulphide bridges and other attractions or repulsions between molecules.
  • Quarternary structure – two or more polypeptide chains folded together to form a complex protein.

Week 2: Transport across the plasma membrane

Image result for phagocytosis and pinocytosis

Learning Intention:
“Students will understand the role of different organelles including ribosomes, endoplasmic, reticulum, Golgi apparatus and associated vesicles in the export of a protein product from the cell through exocytosis and cellular engulfment of material by endocytosis.”

Ribosomes translate the messenger RNA into a protein by matching the 3-base pair codon with an anticodon on the transport RNA, allowing the production of a polypeptide. The endoplasmic reticulum allows the transport of polypeptides (protein chains) to the Golgi aparatus, where proteins are collected, packaged and distributed throughout the cell and exported through the cell membrane (exocytosis).

Osmosis is the passive movement of water across a semi-permeable membrane
Diffusion is the natural tendency of particles to move from a higher concentration to a lower concentration. It is a passive process – does not require energy to be expended.
Facilitated diffusion is when a protein channel is required to allow the passive movement of larger molecules through the cell membrane.
Active transport (as opposed to passive transport) means that energy is required for the cell to all transport of substances against the concentration gradient.
Phagocytosis is the movement of solids across a membrane, usually when the cell creates a pocket and engulfs the nutrient.
Pinocytosis is the movement of liquids across a membrane, for example, when a Paramecium expels liquid waste water.
Endocytosis is when substances move into the cell.
Exocytosis is when substances move out of the cell.

Week 1: Fluid mosaic model of the cell membrane

Image Source

Which molecules can move through the cell membrane passively (by diffusion)?

Which molecules can move through the cell membrane by active transport (requiring energy)?

Which molecules cannot pass through the cell membrane?