Test 1 Flashcards
Enzymes (definition)
Enzymes are biological catalysts composed of globular proteins. Their function depends on the presence of an active site, a specific region where substrates bind to undergo chemical transformation. Factors such as high temperature, extreme pH levels, and other environmental conditions can lead to denaturation, altering enzyme structure and function.
The rate of enzyme activity is influenced by various factors, including temperature, pH, enzyme concentration, substrate concentration, inhibitors, coenzymes, and cofactors. Inhibitors are classified into competitive, which bind to the active site, and non-competitive, which bind elsewhere on the enzyme, altering its function. Coenzymes and cofactors, which include vitamins and minerals, assist enzymes in their catalytic role.
Photosynthesis
Photosynthesis occurs within chloroplasts, specifically in the thylakoids, stroma, and grana. The process is divided into stages, each contributing to the overall conversion of light energy into chemical energy. The net equation for photosynthesis is:
6CO2(g) + 6H2O(g) → C6H12O6(aq) + 6O2(g)
The rate of photosynthesis is influenced by temperature, carbon dioxide concentration, and light intensity. The process consists of light and dark reactions, where water is split to release oxygen, and carbon dioxide is reduced to form glucose.
Respiration
Mitochondria play a crucial role in aerobic respiration by generating ATP, the cell’s energy currency. Cellular respiration occurs in distinct stages:
Glycolysis
Krebs cycle
Electron transport chain
The net equation for aerobic respiration is:
C6H12O6(aq) + 6O2(g) → 6CO2(g) + 6H2O(g) + 36-38 ATP
Factors affecting respiration rates include temperature, glucose concentration, oxygen concentration, and pH.
DNA Structure and Replication
DNA, or deoxyribonucleic acid, is a double-stranded molecule located in the nucleus of eukaryotic cells. It consists of nucleotides made up of a phosphate group, deoxyribose sugar, and nitrogenous bases. Base pairing follows the complementary rule: A-T and C-G.
Replication involves several enzymes:
Helicase: unwinds DNA strands
Primase: adds RNA primers
DNA polymerase: synthesizes new DNA strands
Ligase: joins Okazaki fragments
DNA replication follows the semi-conservative model, ensuring genetic continuity. Enzymes such as polymerase, ligase, and endonucleases can be used to manipulate DNA in genetic studies, including genome sequencing.
Protein Synthesis
Proteins perform diverse functions, including acting as enzymes. Genes are composed of coding (exons) and non-coding (introns and regulatory) regions. Protein synthesis occurs in two main steps:
Transcription: DNA is transcribed into mRNA in the nucleus.
Translation: mRNA is translated into an amino acid sequence at the ribosome, involving tRNA, codons, and anticodons.
Gene expression in prokaryotes is regulated by mechanisms such as the lac operon. Phenotypic expression is influenced by transcription and translation factors, gene interactions, and environmental conditions. Differential gene expression directs cell differentiation, contributing to tissue formation and growth-related structural changes.
Limiting factor
Prevents something from occurring at maximum rate.
lacl gene
The LacI gene codes for the repressor protein (½), which in the absence of lactose binds to
the operator (½) which prevents transcription of the structural genes (½). When
lactose/allolactose is present, it binds to the repressor (acts as an inducer) (½) which changes
the repressor’s shape (½), causing it to be released from the operator (½). This allows RNA
polymerase to bind to the promotor (½) and transcribe the structural genes of the lac operon
(½).
Effectiveness of lac operon (using E. Coli)
When E.coli in the gut of animals is surrounded by glucose, its preferred energy source, it
does not waste energy making enzymes/proteins involved in lactose digestion, so lac operon
is switched off (1). When the gut habitat of E.coli changes to lactose, the lac operon enables
E. coli to gain energy from a different source providing flexibility in its food environment (when
glucose is absent) (1).
Allows e.coli to access different food sources in a changing environment.
Alcoholic fermentation definition
Alcoholic fermentation is a metabolic process in which glucose (or other sugars) is converted into ethanol (alcohol) and carbon dioxide by the action of yeast or certain bacteria, in the absence of oxygen.
This anaerobic process allows cells to generate ATP, the energy currency, in environments where oxygen is unavailable.
During alcoholic fermentation, glucose undergoes glycolysis to form pyruvate, which is then converted into ethanol and CO₂, producing a small amount of energy. Alcoholic fermentation is commonly used in the production of alcoholic beverages and bread.
Activator (enzymes):
An activator is a molecule or protein that increases the rate of a biological process by enhancing the function of an enzyme or a gene. In gene expression, activators are transcription factors that bind to enhancer regions of DNA, helping RNA polymerase initiate transcription. In enzymatic reactions, activators bind to enzymes to increase their catalytic activity, making biochemical processes more efficient.
Product inhibition:
Product inhibition is a regulatory mechanism in which the final product of a metabolic pathway inhibits an earlier enzyme in the same pathway, preventing overproduction. This form of negative feedback helps maintain homeostasis by conserving energy and resources.
CHLOROPLAST DEFINITION
This is an organelle that is only found in autotrophs and consists of special green membranes called THYLAKOIDS. These thylakoids are arranged into stacks (like a column of coins) called GRANA (plural). The stacks can be linked by thylakoids, known as intergranal thylakoids (lamellae). The thylakoids float in a liquid cytoplasm forming a membrane free region called the STROMA. The thylakoids are green due to the presence of chlorophyll.
Electron transport chain (respiration):
The electron transport chain (ETC) in cellular respiration is a series of protein complexes embedded in the inner mitochondrial membrane. Electron carriers (NADH and FADH₂) donate electrons, which move through the complexes, pumping protons (H⁺) across the membrane. This creates a proton gradient, and as protons diffuse back through ATP synthase, ATP is produced. Oxygen acts as the final electron acceptor, forming water.
What is the trp operon?
The trp operon is a group of genes in bacteria (like E. coli) that regulate the production of tryptophan, an essential amino acid.
Is the trp operon inducible or repressible?
The trp operon is repressible, meaning it is usually on but can be turned off when tryptophan is present.
What happens when tryptophan levels are high?
Tryptophan binds to the trp repressor, activating it. The repressor then binds to the operator, blocking RNA polymerase and stopping transcription.
What happens when tryptophan levels are low?
The trp repressor is inactive, and RNA polymerase can transcribe the operon’s genes, leading to the production of tryptophan.
What is the role of the operator in the trp operon?
The operator is a DNA sequence where the trp repressor binds to turn off the operon when tryptophan is present.
Why are biochemical pathways important?
‘A lot of important reactions are complex and involve making a number of discrete chemical changes resulting in a lot of intermediate compounds, which requires a series of enzymes to catalyse each sub-reaction.’
