Photosynthesis and Cellular Respiration

Photosynthesis and Cellular Respiration

All cellular activities require energy.

Directly or indirectly nearly all energy for life comes from the sun.

Autotrophs: organisms that can make their own food. Plants convert light energy from the sun into chemical energy.

Hetertrophs: organisms that need to ingest food to obtain energy.

All of the chemical reactions in a cell are referred to as the cell’s metabolism. Two types of metabolic pathways:

Catabolic- release energy by breaking down larger molecules into smaller molecules

Anabolic- use energy released by catabolic pathways to build larger molecules from smaller molecules. This relationship allows continual flow of energy within an organism.

Photosynthesis is the anabolic pathway in which light energy from the Sun is converted to chemical energy for use by the cell. CO2 + H2O + light C6H12O6 + O2

Cellular respiration is a catabolic pathway in which organic molecules are broken down to release energy for use by the cell. C6H12O6 + O2 CO2 + H2O + about 38 ATP

Adenosine triphosphate – ATP- is the most important biological molecule that provides chemical energy.

ATP is the most abundant energy-carrier molecule in cells and is found in all types of organisms.

ATP is made of an adenine base, a ribose sugar, and three phosphate groups. Adenosine = Adenine + ribose sugar Triphosphate – 3 phosphate groups

Where energy is “found”

ATP releases energy when the bond between the second and third phosphate groups is broken forming a molecules called adenosine diphosphate- ADP

Cells use ATP to perform 3 types of work Chemical, mechanical, and transport

ATP is continuously converted to ADP as cells do work ADP can be converted back to ATP

Photosynthesis and Cellular Respiration

Photosynthesis occurs in two phases. Phase 1(Light reactions): light-dependent reactions, light

energy is absorbed and then converted into chemical energy in the form of ATP and NADPH.

Phase 2 (Calvin Cycle): light –independent reactions, the ATP and NADPH that were formed in phase one are used to make glucose. Once glucose is produced, it can be jointed to other simple

carbohydrates and form larger molecules = STARCH!

Two steps in the process of photosynthesis Phase 1: Light Reactions

Phase 2: Calvin Cycle

6CO2 + 6H2O + light C6H12O6 + 6O2

Chloroplasts-large organelles that capture light energy in photosynthetic organisms (mainly found in leaf cells)

Two main compartments essential for photosynthesis: #1: Thylakoids- flattened saclike

membranes that are arranged in stacks. Light-dependent reactions take place

within the thylakoids.

Thylakoids form stacks called grana.

#2: Stroma- the fluid-filled space that is outside the grana. Light-independent reactions in phase 2 of

photosynthesis occur here.

chloroplast

stroma

grana (thylakoids)

Pigment: light-absorbing colored molecules found in the thylakoidmembranes of chloroplasts. Pigments differ in their ability to absorb

specific wavelengths of light.

Major light-absorbing pigments in plants are chlorophylls. Chlorophyll absorbs red & blue light and

reflects green light. This is why leaves appear green!

Also contain accessory pigments which allow plants to trap additional light energy from other areas of the visible spectrum. Carotenoids reflect yellow, orange, and red.

Give carrots and sweet potatoes their color. Also visible in fall when leaves are changing

colors.

chloroplast

leaf cell

leaf

The structure of the thylakoid membrane is the key to the efficient energy transfer during electron transport.

Light energy excites electrons in photosystem II

Light energy causes a water molecule to split. When water splits, oxygen is released from the cell, protons (H+ ) stay in the thylakoid space and an activated electron enters the electron transport chain.

Excited electrons move from photosystem II to an electron acceptor in thylakoid membrane.

Electrons are transferred to photosystem I.

Electrons are re-energized and transferred to the protein ferrodoxin (final electron acceptor)

NADPH is formed from NADP+ +H+

ATP is produced in conjunction with electron transport by the process of chemiosmosis- mechanism by which ATP is produced as a result of the flow of electrons down a concentration gradient.

Breakdown of water molecule is essential for providing electrons for ETC and providing the H+ necessary to drive ATP synthesis.

The H+ released during electron transport accumulate in the interior of the thylakoid. Due to a high concentration of H+ in thylakoid and low

concentration of H+ in stroma the H+ diffuses down the concentration gradient into the stroma. This helps in allowing ATP synthesis to occur in the stroma.

Calvin Cycle- energy is stored in organic molecules such as glucose. Also known as light-independent reactions

Step 1-involves carbon fixation: 6 carbon dioxide molecules (CO2) combine with six 5-carbon compounds =

twelve 3-carbon molecules called 3-phosphoglycerate (3PGA)

Step 2- Chemical energy stored in ATP and NADPH is transferred to the 3-PGA molecules which forms high-energy molecules called glyceraldehyde 3- phosphate (G3P)

Step 3- two G3P molecules leave the cycle to be used for the production of glucose & other organic compounds.

Step 4-Enzyme rubisco converts the remaining 10 G3P into 5-carbon molecules called ribulose 1,5-bisphosphates (RuBP) Rubisco converts inorganic carbon dioxide molecules into

organic molecules that can be used by the cell, it is considered one of the most important biological enzymes.

Many plants in extreme climates have alternative photosynthesis pathways to maximize energy conversion.

C3 plants: do not have an alternative pathway Examples: wheat, pears, peanuts

C4 plants: fix CO2 into four carbon compounds instead of three in Calvin Cycle Able to keep stomata closed during hot days, while the carbon

compounds are transferred to special cells. Examples: Crab grass, sugarcane, corn

CAM plants: allows CO2 to enter the leaves only at night when atmosphere is cooler and CO2 is fixed. During the day CO2 goes into the Calvin Cycle. occurs in water conserving plants such as pineapple, orchids,

and cacti

Photosynthesis and Cellular Respiration

The function of cellular respiration is to harvest electrons from carbon compounds such as glucose, and use that energy to make ATP. Occurs in mitochondria

Structure of mitochondria aids with this process

Inner and outer membrane (many folds)

Lots of surface area allows for many reactions to occur at once

C6H12O6 + 6O2 6CO2 + 6H2O + ATP

2 main parts to cellular respiration: Glycolysis- is an anaerobic process

Anaerobic= NO OXYGEN REQUIRED

Aerobic respiration- includes the Krebs cycle and electron transport. Aerobic= REQUIRES OXYGEN

Glucose is broken down in the cytoplasm through the process of glycolysis. Glycolysis means “sugar splitting” which is exactly what it does

Two molecules of both ATP and NADH are formed for each molecule of glucose broken down.

2 ATP is required to start the reactions that will produce energy for the cell.

Electrons are passed to carriers NAD+ & NADH

4 ATP are produced by glycolysis.

Pyruvic Acid molecule is produced Most of the energy is still in this

2 ATP molecules are used to split glucose

4 ATP molecules are produced

2 molecules of NADH produced

2 molecules of pyruvate produced

Glucose + 2 ATP 4 ATP + 2 Pyruvic Acid + 2 NADH

Krebs cycle is also known as Citric Acid Cycle and Tricarboxylic Acid Cycle (TCA cycle)

Prior to the Krebs cycle, pyruvate first reacts with coenzyme A (CoA) which forms acetyl CoA.

NAD+ is converted to NADH

Acetyl CoA moves to mitochondrial matrix and 2 CO2 molecules and 2 NADH are produced.

Krebs Cycle starts with Acetyl CoA

Final step in the breakdown of glucose.

90% of the ATP is produced here

Overall, electron transport produces 24 ATP. Each NADH molecule produces three ATP and each group of three FADH2 produces two ATP. In eukaryotes, one molecule of glucose yields 36 ATP

In prokaryotes , one molecule of glucose yields 38 ATP

The electron transport chain (E.T.C) uses NADH and FADH2

to make ATP. high-energy electrons enter electron transport chain

energy is used to transport hydrogen ions across the inner membrane

hydrogen ionsflow through achannel in themembrane

The breakdown of one glucose molecule produces up to38 molecules of ATP.

• ATP synthase produces ATP

• oxygen picks up electrons and hydrogen ions

• water is released as a waste product

Some cells can function for a short time with oxygen is low.

Cells can continue to produce ATP through glycolysis , however glycolysis only makes a net gain of 2 ATP and a cell has a limited amount of NAD+. Glycolysis will stop when NAD+ is all used up and cant be replenished...

In order to replenish NAD+ and produce a small amount of ATP an anaerobic pathway will follow glycolysisknown as fermentation.

Fermentation – process of making ATP without oxygen No extra ATP is produced

Only what is made in glycolysis

There are two main types of fermentation Lactic Acid Fermentation

Enzymes convert pyruvate made during glycolysis to lactic acid

Commonly done by fungi & bacteria Produces some food (cheeses, yogurt, soy sauce, saurkraut)

Can be done in the human body- skeletal muscles produce lactic acid… Sore muscles after hard work anyone?

Alcohol Fermentation Chemical reaction when pyruvate is converted to ethyl

alcohol and carbon dioxide. Commonly done by yeasts

Produces many foods that we eat Produces Alcohol & CO2

Equation for cellular respiration is the opposite of photosynthesis.