From glucose to pyruvate
First step of respiration.
Fuel in the cell
A cell gets energy by breaking down food. One such food molecule is glucose, which has six carbon atoms.
What do you think the cell does first with glucose?
What this lesson covers
The idea
In all organisms the first step of respiration is the break-down of glucose, a six-carbon molecule, into a three-carbon molecule called pyruvate, in the cytoplasm.
Fuel in the cell
A cell gets energy by breaking down food. One such food molecule is glucose, which has six carbon atoms.
What do you think the cell does first with glucose?
- Breaks it into a smaller molecule
- Joins it into a bigger molecule
- Throws it out unchanged
Break the glucose
Press Next step.
The same first step
Organisms can use oxygen or not, but in all of them the first step of respiration is the same. Glucose, a six-carbon molecule, is broken down in the cytoplasm into a three-carbon molecule called pyruvate. What happens to pyruvate afterwards depends on whether oxygen is there.
In all organisms the first step of respiration is the break-down of glucose, a six-carbon molecule, into a three-carbon molecule called pyruvate, in the cytoplasm.
Notes
In all organisms respiration starts with glucose (6 carbons) breaking down into pyruvate (3 carbons) in the cytoplasm.
Check yourself
How many carbon atoms does one glucose molecule have?
Answer: 6
The book calls glucose a six-carbon molecule.
What is the three-carbon molecule made when glucose is first broken down?
Where in the cell does glucose break down to pyruvate?
Which statement is correct?
- Pyruvate — correct. Yes!
- Lactic acid. Lactic acid is made later, from pyruvate, when muscle cells lack oxygen.
- Ethanol. Ethanol is made later, from pyruvate, in yeast during fermentation.
- In the mitochondria. The mitochondria are where pyruvate is broken down using oxygen.
- In the cytoplasm — correct. Yes!
- In the chloroplasts. Chloroplasts hold chlorophyll and are where photosynthesis occurs; glucose breaks down to pyruvate in the cytoplasm.
- Only organisms that use oxygen break glucose into pyruvate. In all cases, with oxygen or without, the first step is the break-down of glucose into pyruvate.
- Pyruvate has six carbon atoms. Pyruvate is a three-carbon molecule; glucose has six.
- In all organisms the first step of respiration is glucose breaking down to pyruvate — correct. Yes!