Cellular Respiration Part 1: Glycolysis

Summary

Professor 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

00:00

🌞 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.

05:03

🔬 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.

Keywords

💡Glycolysis

Glycolysis is the metabolic pathway that converts glucose into pyruvate, producing energy in the form of ATP. It is the first step in cellular respiration and occurs in the cytoplasm of the cell. In the video, glycolysis is described as an anaerobic process that does not require oxygen, making it an ancient metabolic pathway found in even the simplest cells. The script details the 10-step process of glycolysis, starting with glucose and ending with the formation of two pyruvate molecules, a net gain of two ATP molecules, and the release of two NADH molecules.

💡Cellular Respiration

Cellular respiration is the set of metabolic processes by which cells break down biomolecules to generate energy. The script explains that it is also known as aerobic respiration because it requires oxygen. Cellular respiration encompasses glycolysis, the citric acid cycle, and oxidative phosphorylation. The theme of the video revolves around how these processes facilitate the production of energy that cells can use for various functions, highlighting the importance of glucose as the starting material.

💡Aerobic Respiration

Aerobic respiration is a specific type of cellular respiration that requires oxygen. The script mentions that organisms breathe in oxygen to facilitate this process. It is through aerobic respiration that glucose is metabolized in the presence of oxygen to produce carbon dioxide, water, and energy. The video emphasizes the role of oxygen in this process, which is essential for the conversion of glucose into usable energy.

💡Glucose

Glucose is a simple sugar that serves as the primary source of energy for cells. In the script, glucose is described as the starting material for metabolic processes in our bodies. It is produced by plants through photosynthesis and is either consumed as starch or broken off from glycogen stored in cells. The video explains how glucose is converted into pyruvate through glycolysis, which is a critical step in generating energy for cellular activities.

💡ATP

ATP, or adenosine triphosphate, is the primary energy currency of the cell. The script explains that during glycolysis, a net of two ATP molecules is produced from one glucose molecule. ATP is crucial for various cellular processes as it provides the energy needed for these activities. The video outlines the investment of two ATPs in the preparatory phase of glycolysis and the return of four ATPs in the payoff phase.

💡NAD+ and NADH

NAD+ (nicotinamide adenine dinucleotide) and its reduced form, NADH, are electron carriers that play a critical role in metabolic pathways. The script describes NAD+ as having a positively charged nitrogen atom and being able to accept electrons and hydrogen ions to become NADH. This transfer is facilitated by dehydrogenase enzymes and is essential for the breakdown of glucose during glycolysis.

💡Citric Acid Cycle

The citric acid cycle, also known as the Krebs cycle or TCA cycle, is a series of chemical reactions that generate energy through the oxidation of acetyl-CoA derived from carbohydrates, fats, and proteins. The script mentions this cycle as one of the three major pathways of cellular respiration that follows glycolysis. It is a key part of aerobic respiration where pyruvate from glycolysis is further processed to produce ATP, NADH, and CO2.

💡Oxidative Phosphorylation

Oxidative phosphorylation is the process of producing ATP using electrons from NADH and FADH2, which are passed along the electron transport chain. The script identifies this as the third major pathway of cellular respiration. It is where the majority of ATP is produced during aerobic respiration, highlighting the efficiency of this process in generating energy.

💡Pyruvate

Pyruvate is the end product of glycolysis and serves as an important intermediate in cellular respiration. The script explains that glucose molecules are split into two pieces of pyruvate during glycolysis. Pyruvate then moves on to the next stages of cellular respiration, entering the mitochondria where it is further metabolized in the citric acid cycle.

💡Photosynthesis

Photosynthesis is the process by which plants, algae, and some bacteria convert light energy into chemical energy in the form of glucose or other sugars. The script mentions that plants use sunlight, carbon dioxide, and water to make glucose, which is then used as the starting material for cellular respiration. This process is crucial for the energy cycle on Earth, as it provides the energy source for all aerobic organisms.

💡Dehydrogenase

Dehydrogenase is a class of enzymes that catalyze the transfer of electrons from NAD+ to NADH during oxidation-reduction reactions. The script describes the role of dehydrogenase in facilitating the electron exchanges that occur in metabolic pathways, specifically in the breakdown of glucose during glycolysis. This enzyme is essential for the conversion of glucose into pyruvate and the production of energy.

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: