Lab Practical Review
Lab Practical Overview
Labs 8, 9, 10, and 11 - Lab 9: Vapor Chromatography and Respiration (conducted in one day) - Lab 10: Gene Extraction and Electrophoresis - Mitosis and Gene Explorer completed this week.
Enzyme Lab
Preparation for the lab practical involves several steps: 1. Attention in Lab: Understand what is done and why. 2. Review Handouts: Critical for understanding the enzymes involved.
Key Definitions
Enzymes: Biological catalysts that facilitate chemical reactions.
Substrates: Reactants that enzyme acts upon.
Product: Result of an enzyme-substrate reaction.
Recovery of Enzymes: Enzymes remain unchanged and are recoverable post-reaction.
Example from Lab
Enzyme Used: Catalase
Source: Potato juice or extract
Substrate: Hydrogen Peroxide ()
Interest in Products: Oxygen (primary interest), Water (also produced but secondary interest).
- Proxy for Enzyme Activity: The amount of oxygen produced indicates enzyme activity rate.
Experiment Variables
Independent Variables (Manipulated): - Temperature - Substrate Concentration - Enzyme Concentration - pH - Presence of Inhibitors (substances that reduce enzyme activity)
Dependent Variable (Measured): Rate of enzyme activity demonstrated by oxygen levels.
Data Analysis
When presented with data: - Identify independent variable changed (e.g., enzyme concentration). - Draw conclusions regarding enzyme activity rate based on provided data.
Key Concepts in Enzyme Function
Optimal conditions for enzyme activity: - Identify temperature or pH at which activity is maximized based on experimental data.
Denaturation: Loss of enzyme activity due to extreme temperatures or pH. - Inactivation vs. Denaturation: - Inactivation is reversible (e.g., cooling); Denaturation is irreversible (e.g., excessive heat).
Spectrophotometry Lab
Principles and Equipment
Definition: Technique used to measure light absorbance or transmittance by solutions.
Instrument Used: Spectrophotometer.
Wavelength Range: 100 to 1000 nm (visible light range).
Absorbance vs. Transmittance: - Absorbance: Amount of light absorbed by a sample. - Transmittance: Amount of light that passes through a sample.
Experimental Procedure
Calibration: - Set spectrophotometer to the desired wavelength (e.g., 460 nm). - Use a blank sample to zero the device.
Sample Measurement: Insert spinach extract or other sample. - Record the absorbance without re-zeroing.
Data Interpretation
Identify peaks in absorbance spectra to determine maximum absorption wavelengths for pigments.
Peaks in the Graph: The graph will have tall spikes called peaks. These peaks indicate that the pigment is absorbing a lot of light at specific colors (wavelengths).
Finding Maximum Absorption Wavelengths: The highest point of each peak shows us the maximum absorption wavelength for that pigment. This tells us which color of light the pigment uses the most for processes like photosynthesis, helping us understand how plants absorb sunlight effectively.
Understand the practical applications of absorbance data in assessing concentration and reactions in the lab.
Measuring Concentration: When we know how much light a solution absorbs, we can figure out how concentrated the substance is. If a solution absorbs more light, it usually means there's more of the substance in it.
Tracking Reactions: Absorbance data can also show us how reactions are happening over time. For example, if a reaction produces a product that changes color, we can measure the absorbance to see how quickly the reaction
Paper Chromatography Lab
Principles and Techniques
Purpose: Separate pigments in a sample (e.g., spinach leaves).
Mobile Phase: Solvent (e.g., acetone) that moves up the chromatography paper.
Stationary Phase: Chromatography paper, which remains stationary.
Pigments Involved: Carotene, xanthophyll, chlorophyll a, chlorophyll b (separation and identification).
Key Techniques
Determine relative movement of pigments on paper, identify colors, and interpret movement speeds.
Movement of Pigments: When we place a mixture of pigments in a solvent, each pigment travels differently up the paper. Some pigments move faster, while others move slower. This speed difference helps us see which colors are in the mixture.
Identifying Colors: As the pigments move, they separate into distinct spots based on their colors. By observing these spots, we can identify which pigments are present in our sample.
Interpreting Movement Speeds: The distance a pigment travels compared to how far the solvent moves helps us understand how quickly each pigment moves. Faster-moving pigments go further up the paper, while slower ones stay closer to the starting point. This can give us clues about their properties and how they react in different situations.
Note on RF Values: Do not compute RF values unless explicitly asked in instructions.
Photosynthesis and Cellular Respiration Lab
Key Concepts
Positive and Negative Slopes in Data Analysis:
- Positive slope in oxygen production indicates increased oxygen levels.
- Negative slope indicates oxygen usage or increased carbon dioxide levels.
Key Conditions
Changes in slopes relate to processes in photosynthesis vs. cellular respiration.
Photosynthesis Condition: Produces oxygen, positive slope for oxygen.
Cellular Respiration Condition: Consumes oxygen, positive slope for carbon dioxide.
Equations to Know
Photosynthesis Equation:
Cellular Respiration Equation:
DNA Extraction Lab
Key Techniques and Materials
Materials Used: Meat tenderizer (breaks proteins), salt (neutralizes charges), detergent (breaks down membranes), cold alcohol (precipitates DNA).
Key Understandings
Explain how each material contributes to the extraction process.
Electrophoresis Lab
Principles
Purpose: Separate DNA fragments by size.
Smaller DNA fragments travel faster than larger ones.
Equipment and Procedures
Electrophoresis Setup: Used to create bands observed under UV light for analysis.
Buffer Used: TBE buffer (Tris, Borate, EDTA).
Data Interpretation
Identify DNA bands (blue bands containing DNA). Interpret results in context of forensic analysis or paternity tests.
Identifying DNA Bands: In electrophoresis, DNA fragments are separated by size, resulting in distinct bands based on fragment length, often observed as blue bands when stained.
Import of DNA Bands: Each band represents a different fragment size, which can be analyzed to identify genetic similarities or differences between samples.
Interpretation in Forensic Analysis: In forensic contexts, matching DNA bands between suspect and crime scene samples can indicate potential involvement in a crime.
Applications in Paternity Tests: In paternity tests, DNA bands from a child are compared to those from the alleged parents. Bands that appear in the child must also be present in one or both parents, providing evidence for or against paternity.
Mitosis and Gene Explorer Lab
Mitosis Stages
Familiarity with phases of mitosis: Interphase, Prophase, Metaphase, Anaphase, Telophase, and Cytokinesis.
Mitosis Phases:
- Interphase: Preparation phase, where DNA is replicated.
- Prophase: Chromatin condenses into chromosomes, and the nuclear envelope begins to break down; spindle fibers emerge.
- Metaphase: Chromosomes align at the metaphase plate; spindle fibers attach to the centromeres of chromosomes.
Anaphase: Sister chromatids are pulled apart towards opposite poles of the cell. -
Telophase: Chromatids reach the poles, nuclear envelopes reform around each set of chromosomes, and the chromosomes begin to de-condense back into chromatin.
Gene Explorer Tasks
Promoter and Sequence Identification: Understand sequence locations (promoter vs. coding gene).
Promoter: Think of the promoter as the "start signal" for the gene. It's a special region of DNA where a protein called RNA polymerase attaches to begin making mRNA. You can imagine it as a "starter" button that tells the cell, "Hey, it's time to start using this gene!"
Coding Gene: This is the actual section of DNA that contains the instructions for making a protein. It’s made up of sequences of nucleotides, which are like the letters in a recipe. When the gene is used, the coding gene's information gets copied into mRNA, which will then be translated
- Exons (coding segments) and Introns (non-coding segments)
Be able to transcribe sequences into mRNA and translate mRNA into amino acid sequences.
Transcription into mRNA:
- The process begins with the DNA sequence that includes a gene.
- During transcription, RNA polymerase binds to the promoter region of the gene and separates the DNA strands.
- The RNA polymerase then synthesizes a single strand of mRNA using the template DNA strand. Each nucleotide in the DNA is paired with its complementary RNA nucleotide (A with U instead of T, and C with G).
- Once completed, the mRNA strand detaches, and the DNA strands re-anneal.
Translation of mRNA into Amino Acids: - The mRNA strand is translated into a protein at the ribosome.
\- The ribosome reads the mRNA in sets of three nucleotides (codons).
- Each codon corresponds to a specific amino acid, as defined by the genetic code.
- tRNA (transfer RNA) molecules bring the appropriate amino acids to the ribosome, based on the codon.
- The amino acids are linked together in a growing polypeptide chain until a stop codon is reached, indicating the end of translation, resulting in a completed protein.
Key Concepts for Mutations
Identification and understanding of types of mutations (missense, nonsense, frameshift, silent).
Missense Mutation: This happens when a change in one DNA letter causes one amino acid in the protein to be swapped for another. This change can have different effects on how the protein works. For example, in sickle cell anemia, a missense mutation changes one amino acid in hemoglobin, the protein that carries oxygen in blood, leading to health problems.
Nonsense Mutation: In this type of mutation, a single DNA change makes a regular amino acid codon turn into a stop codon, which tells the cell to stop making the protein too soon. This results in a protein that is cut short and usually doesn't work properly. If this happens early in making the protein, it can cause bigger problems.
Frameshift Mutation: This mutation occurs when DNA has a letter added or removed, changing how the rest of the DNA is read. This shift means that every amino acid after the mutation is different, which can lead to a completely messed-up protein. Frameshift mutations usually cause more damage than other types of mutations.
Silent Mutation: This is a change in the DNA that doesn’t affect the outcome of the protein at all
Recognizing the effect of mutations at the level of DNA and resulting amino acid sequences.
- Missense Mutation: This mutation changes one letter in the DNA, resulting in the replacement of one amino acid in a protein with another. This can be important because some amino acids are crucial for a protein's job. For example, in sickle cell anemia, an important protein called hemoglobin, which carries oxygen in the blood, has a change. This small change makes the red blood cells misshapen and unable to carry oxygen efficiently, leading to health issues like pain and fatigue.
- Nonsense Mutation: In this mutation, a letter change creates a stop signal instead of the code for an amino acid. This means that the protein stops being made too early. When the protein is cut short, it usually doesn’t work properly. If this happens early in the protein chain, the cell ends up making a bad version of the protein, which can lead to serious problems, like diseases or developmental issues.
- Frameshift Mutation: This type occurs when a letter is added or removed from the DNA. Because of this change, the reading frame of the DNA shifts, which means all the following amino acids are different from what they should be. Imagine reading a sentence where a letter got lost; suddenly everything after that makes no sense. This can create a completely messed-up protein that rarely works as it should. Frameshift mutations can lead to major disorders because they disrupt the entire protein being made.
- Silent Mutation: This mutation changes a DNA letter but does not change the amino acid that is produced because of how the genetic code works. The protein remains the same and works just fine. So, while there is a change in the DNA, it has no effect on how the protein functions or on the organism, making it a harmless mutation.