Cellular Respiration Part 1: Glycolysis
Summary
TLDRProfessor Dave's lecture delves into the fundamental process of glycolysis, a crucial metabolic pathway for energy production in cells. Starting with the sun's energy, he explains how plants convert sunlight into glucose through photosynthesis. This glucose is then used by our bodies in the process of cellular respiration, which breaks down glucose into energy, carbon dioxide, and water. Glycolysis, the first step in this process, occurs in the cytoplasm and involves the conversion of one glucose molecule into two pyruvate molecules, yielding a net of two ATP molecules. The process requires 10 enzymes and is both anaerobic and the most evolutionarily ancient. The video script also includes a detailed breakdown of each step in glycolysis, providing a comprehensive understanding of the process.
Takeaways
- 🌞 Energy for all our activities comes from the sun, which is the source of energy for life on Earth.
- 🌱 Plants produce energy through photosynthesis, using sunlight, carbon dioxide, and water to create glucose.
- 🔋 Cellular respiration is the process by which cells generate energy, and it involves the breakdown of biomolecules to produce energy.
- 🧬 Glucose, obtained from starch or glycogen, is the primary substrate in aerobic respiration.
- 🌬️ Oxygen is essential for aerobic respiration, as it facilitates the process in organisms that breathe it in.
- 🔄 Glucose is converted into carbon dioxide, water, and energy through metabolic pathways.
- 🚀 The process is analogous to combustion reactions, with the energy released similar to that in engines.
- 🧲 Metabolic pathways involve electron carriers like NAD+ and NADH, which play a crucial role in the breakdown of glucose.
- 🔄 The electron exchanges in these pathways are facilitated by enzymes, such as dehydrogenase.
- 🧬 Glycolysis, the first step in cellular respiration, occurs in the cytoplasm and involves the splitting of glucose into pyruvate.
Q & A
What is the primary source of energy for cellular respiration?
-The primary source of energy for cellular respiration is glucose, which is produced by plants through photosynthesis using sunlight, carbon dioxide, and water.
Why is oxygen necessary for aerobic respiration?
-Oxygen is necessary for aerobic respiration because it is used in the process to convert glucose into carbon dioxide, water, and energy through metabolic pathways.
What is the role of NAD+ and NADH in cellular respiration?
-NAD+ and NADH act as electron carriers in cellular respiration. NAD+ can accept electrons and become NADH, which is then used in various metabolic reactions, including the breakdown of glucose.
What are the three major pathways of cellular respiration?
-The three major pathways of cellular respiration are glycolysis, the citric acid cycle (also known as the Krebs cycle or TCA cycle), and oxidative phosphorylation.
Where does glycolysis take place within a cell?
-Glycolysis takes place in the cytoplasm of the cell, and it is an anaerobic process, meaning it does not require oxygen.
What is the net yield of ATP from one molecule of glucose during glycolysis?
-The net yield of ATP from one molecule of glucose during glycolysis is two ATP molecules.
How many enzymes are involved in the glycolysis process?
-There are 10 enzymes involved in the glycolysis process, each catalyzing a specific step in the pathway.
What is the purpose of the preparatory phase in glycolysis?
-The preparatory phase in glycolysis involves two ATP investments to phosphorylate glucose, resulting in the formation of two molecules of GADP, which sets the stage for the payoff phase where ATP is generated.
What happens to the glucose molecule during the glycolysis process?
-During glycolysis, the glucose molecule is split into two molecules of pyruvate, with the process yielding a net of two ATPs and two NADH molecules.
What is the significance of the enzyme hexokinase in glycolysis?
-Hexokinase is significant in glycolysis as it catalyzes the first step, phosphorylating glucose to glucose 6-phosphate, which traps the molecule inside the cell and initiates the glycolytic pathway.
How does the process of glycolysis relate to the overall process of cellular respiration?
-Glycolysis is the first step in cellular respiration, where glucose is broken down into pyruvate, which then enters the citric acid cycle and eventually leads to oxidative phosphorylation, the final stage where most of the ATP is produced.
Outlines
🌞 Introduction to Glycolysis and Cellular Respiration
Professor Dave introduces the concept of glycolysis, explaining that energy is essential for all activities and is constantly produced by our cells. This energy originates from the sun, with plants converting sunlight, carbon dioxide, and water into glucose through photosynthesis. This glucose then becomes the starting material for cellular respiration, specifically aerobic respiration, which requires oxygen. Glucose is metabolized in the presence of oxygen into carbon dioxide, water, and energy. NAD+ and its reduced form, NADH, play a crucial role in the electron exchanges during these metabolic pathways, facilitated by the enzyme dehydrogenase. Cellular respiration includes three major pathways: glycolysis, the citric acid cycle, and oxidative phosphorylation, with glycolysis being the first and happening in the cytoplasm. It splits glucose into pyruvate and is an anaerobic process, yielding a net of two ATPs after a 10-step process involving specific enzymes.
🔬 Detailed Steps of Glycolysis
The payoff phase of glycolysis is described, starting with the oxidation of GADP to 1,3-bisphosphoglycerate, requiring NAD+ and inorganic phosphate, catalyzed by glyceraldehyde phosphate dehydrogenase. Phosphoglycerate kinase then transfers a phosphate group to ADP, producing one ATP per GADP molecule, totaling two ATPs. Phosphoglycerate mutase moves the phosphate group to form 2-phosphoglycerate, followed by enolase catalyzing dehydration to produce phosphoenolpyruvate. Finally, pyruvate kinase transfers the remaining phosphate group to ADP, generating another ATP and forming pyruvate. The process involves 10 steps: the preparatory phase uses two ATPs to convert glucose to GADP, and the payoff phase generates four ATPs from two GADP molecules, resulting in a net gain of two ATPs. The summary includes a table listing the enzymes and inputs/outputs for each step. The main takeaway is that glycolysis converts glucose into pyruvate in the cytoplasm, setting the stage for the next phase of cellular respiration.
Mindmap
Keywords
💡Glycolysis
💡Cellular Respiration
💡Aerobic Respiration
💡Glucose
💡ATP
💡NAD+ and NADH
💡Citric Acid Cycle
💡Oxidative Phosphorylation
💡Pyruvate
💡Photosynthesis
💡Dehydrogenase
Highlights
Energy needed for all cellular activities comes from cellular respiration.
Energy originates from the sun and is absorbed by plants through photosynthesis.
Glucose from plants is the starting material for metabolic processes in our bodies.
Cellular respiration, or aerobic respiration, converts glucose into carbon dioxide, water, and energy.
NAD+ and NADH play crucial roles in the electron exchanges of metabolic pathways.
Cellular respiration consists of glycolysis, the citric acid cycle, and oxidative phosphorylation.
Glycolysis occurs in the cytoplasm and splits glucose into pyruvate.
Glycolysis is anaerobic and does not require oxygen.
Glycolysis is an ancient metabolic pathway found in even the simplest cells.
Glycolysis yields a net of two ATPs from one glucose molecule.
Glycolysis involves 10 enzymes and 10 steps.
The hexokinase reaction phosphorylates glucose to make glucose 6-phosphate.
Phosphofructokinase 1 catalyzes the phosphorylation of fructose-6-phosphate to fructose-1,6-bisphosphate.
Fructose-1,6-bisphosphate is split into glyceraldehyde-3-phosphate (GADP) and dihydroxyacetone phosphate (DHAP).
The preparatory phase of glycolysis costs two ATP molecules.
The payoff phase of glycolysis produces four ATP molecules.
The net energy production from glycolysis is two ATPs per glucose molecule.
Pyruvate produced from glycolysis moves on to the next stage of cellular respiration.
Transcripts
Hey it's professor Dave, let's talk about glycolysis.
We need energy to do literally anything, from running a race, to simply
breathing. And every cell in your body is furiously producing all this energy all the time.
Where does this energy come from? Well technically it arrives from the sun.
The sun is releasing enormous amounts of energy as a byproduct of nuclear fusion
reactions, and that energy makes its way to earth, where it can be absorbed by
plants through photosynthesis, which we will discuss later.
Plants use sunlight as well as carbon dioxide and water to make glucose, and it
is all of this glucose, among other biomolecules, that becomes the starting
material for metabolic processes in our bodies. This degradation of biomolecules
to generate energy that cells can use is called cellular respiration, or sometimes
more specifically, aerobic respiration. Let's see how this works,
looking at glucose as the substrate. Aerobic respiration requires oxygen so
any organism that breathes in oxygen from the atmosphere is doing so in order to
facilitate aerobic respiration. Glucose, which we can either consume as starch
or break off from glycogen stored in the cell, can be converted through metabolic
pathways in the presence of oxygen into carbon dioxide, which we breathe out,
water, which is most of what we are, and energy, the energy we need to think and move.
This is not unlike the combustion reactions that happen in an engine, so
it's a reasonable analogy to view biological organisms as machines.
The electron exchanges that occur throughout these metabolic pathways
utilize the electron carrier NAD+ and its other form, NADH. This is a
dinucleotide with an interesting base, nicotinamide, that can exist either
as NAD+, with a
positively charged nitrogen atom, or if reduced it can become NADH. This transfer,
facilitated by an enzyme called dehydrogenase, helps catalyze the
breakdown of glucose. Cellular respiration happens over three major
pathways. There's glycolysis, the citric acid cycle, and oxidative phosphorylation.
Let's focus on these one at a time.
Glycolysis comes first, and it happens in the cytoplasm of the cell. This is the
process by which glucose molecules are split into two pieces called pyruvate.
This first pathway is actually anaerobic, meaning it does not require
oxygen, so it is the most evolutionarily ancient metabolic pathway, occurring in
even the simplest cells. In this pathway, one glucose molecule can yield a net of
two ATPs. It requires 10 enzymes to happen which catalyze each of the 10
steps, as well as an investment of two ATP molecules in the preparatory phase to
get four ATPs back over several steps in the payoff phase. The names and
details of each individual reaction may not be of interest to every viewer, but
in case they do interest you,
here is a brief overview of each step. First the hexokinase reaction. The enzyme
hexokinase phosphorylates the oxygen on carbon 6 to make glucose 6-phosphate.
The polar phosphate group traps the molecule inside the cell and also reduces the
concentration of regular glucose inside the cell, which encourages more glucose
to enter by diffusion. This step costs 1 ATP, which provides the necessary
phosphate group for the reaction. Next, glucose-6-phosphate isomerizes to
become fructose-6-phosphate, a process which is catalyzed by phosphoglucoisomerase.
After that is another phosphorylation, this time on the carbon 1
hydroxyl which gives us fructose-1,6-bisphosphate. This step is catalyzed by
phosphofructokinase 1
and it will cost another ATP. Now this molecule is ready to be cleaved
into two smaller ones. Fructose bisphosphate aldolase is a lyase
enzyme that will split fructose-1,6-bisphosphate into a molecule of
glyceraldehyde-3-phosphate, or GADP, and a molecule of dihydroxyacetone phosphate
or DHAP. The DHAP will be converted into another molecule of GADP by the enzyme
triosephosphate isomerase, which leaves us with two molecules of GADP.
That's the end of the five-step preparatory phase, with two ATPs spent to
achieve the two phosphorylations. Now it's time for the payoff phase.
Let's just look at one of our two GADP molecules from the preparatory phase, and
we see that the first thing that will happen is an oxidation to become
1,3-bisphosphoglycerate. This requires NAD+ and a free phosphate, or inorganic
phosphate to occur, and the enzyme involved is called glyceraldehyde
phosphate dehydrogenase. Next, a phosphoglycerate kinase will
catalyze transfer of a phosphate group to ADP to become 3-phosphoglycerate
producing one ATP in the process. Since each of the two GADP molecules will make
one ATP, that's a total of two ATPs, for half the total payoff of glycolysis.
Then, phosphoglycerate mutase transfers the remaining phosphate from this hydroxyl
to the next one over to make 2-phosphoglycerate.
Then, enolase catalyzes a dehydration, resulting in the loss of this hydroxyl group which will
produce phosphoenolpyruvate. And lastly, the remaining phosphate group is
transferred to an ADP by pyruvate kinase, generating another ATP and the pyruvate
we discussed before. So altogether it's a 10-step process. The first five steps comprise
the preparatory phase, which take one molecule of glucose and produce two
molecules of GADP. This will cost two ATP. Then the other five steps make up the
payoff phase, in which each molecule of GADP will be converted into pyruvate,
producing two ATP each in the process, for a total of four, meaning the net
energy production from one molecule of glucose is two ATP. If you are required to
memorize basic facts about glycolysis this should probably suffice, but if you
wish to memorize this process in more detail, here is a table that lists the
necessary enzymes for each step as well as any relevant input or output besides
the actual substrate. Certainly the main thing to remember is that in glycolysis,
glucose in the cytoplasm of the cell is converted into pyruvate, which will then
move on to the next stage of cellular respiration.
Thanks for watching, guys. Subscribe to my channel for more tutorials. and as always, feel free to email me:
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