Energy in a Cell All Cells Need Energy

Energy in a Cell

All Cells Need Energy n Cells need energy to do a variety of work: n Making new molecules. n Building membranes and organelles. n Moving molecules in and out of the cell. n Movement.

Where Does A Cell Get Energy? n Food is broken down to a form the cell can use. n Extra energy is stored in an ATP molecule, a nucleotide.

What Is ATP? n ATP – adenosine triphosphate is a molecule made up of an adenine, ribose, and 3 phosphate groups. Adenine Ribose

How Does ATP Work? Energy is stored in the bond between the second and third phosphate group. n When the bond is broken, energy is released and ADP is formed. n Adenine Ribose

ATP – Energy Currency • • Within a cell, formation of ATP from ADP and phosphate occurs over and over, storing energy each time. As the cell uses energy, ATP breaks down repeatedly to release energy and form ADP and phosphate.

Making Energy n Cells make energy in two ways: n Photosynthesis – takes place in the chloroplasts. n Respiration – takes place in the mitochondria.

Photosynthesis n Autotrophs make their own food by trapping light energy and converting it to chemical energy (carbohydrates).

Photosynthesis n Using light from the sun, plants combine water and carbon dioxide to make sugar. n General Equation: 6 CO 2 + 6 H 2 O + energy Reactants C 6 H 12 O 6 + 6 O 2 Products

Photosynthesis n 2 Reactions n Light Reactions n Calvin Cycle

Photosynthesis n Light Reactions – Light energy is converted to chemical energy to split hydrogen from water. n Takes place in the grana of the chloroplasts (the coinlike stacks of sacs). n Byproducts are oxygen, NADPH, and ATP.

Photosynthesis n Calvin Cycle – ATP and NADPH from the light reactions are used along with CO 2 to form a simple sugar (glucose). n Takes place in the stroma of the chloroplasts (the liquid filling). n Byproducts are C 6 H 12 O 6 (glucose), ADP, and NADP+ (which return to the light

Sunlight O 2 NADP+ ADP ATP H 2 O NADPH CO 2 CHLOROPLAST

Chemosynthesis n Some autotrophs can convert inorganic substances to energy. n Most are adapted to live in conditions where there is no oxygen. n Marshes. n Lake sediments. n Digestive tracts of mammals. n Deep in the ocean.

Respiration n The process of breaking down food molecules to release energy. n Occurs in the mitochondria. n Two types: n Aerobic – requires oxygen. n Anaerobic – requires an absence of oxygen.

Respiration n Two types of anaerobic respiration: n Fermentation – occurs when bacteria break down plants (vegetables and fruit) and release alcohol or vinegar. n Lactic Acid Fermentation – occurs in muscles – a buildup of lactic acid causes soreness.

Respiration n Steps n Glycolysis n Citric Acid Cycle n Electron Transport Chain

Respiration n Glycolysis – glucose is split to form pyruvate. n Takes place in the cytoplasm of the cell. n ATP is a byproduct.

Respiration n Citric Acid Cycle – pyruvate is used to build citric acid (a carbon compound), which is broken down to release ATP. n Takes place in the cristae (the folded membrane in the mitochondrion). n CO 2 is released, and NADH carries hydrogen ions to the electron transport chain.

Respiration n Electron Transport Chain – hydrogen ions are stripped of their energy, and large amounts of ATP are formed. n Takes place in the inner membrane of the mitochondrion. n The used ions are combined with oxygen to form H 2 O.

Heat O 2 H 2 O CO 2 Glucose ATP Pyruvate Electron Transport System NAD+ ATP NADH ATP MITOCHONDRION

Sunlight Heat Photosystem II NADP+ ADP O 2 Photo. System I ATP H 2 O NAD+ NADPH ATP NADH CO 2 Calvin Cycle Glycolysis Glucose CHLOROPLAST Electron Transport System Citric Acid Cycle ATP Pyruvate ATP MITOCHONDRION

Sunlight Heat Photosystem II NADP+ ADP O 2 Photo. System I ATP H 2 O Electron Transport System NAD+ NADPH ATP NADH CO 2 Calvin Cycle Citric Acid Glycolysis Cycle ATP Glucose Pyruvate CHLOROPLAST ATP MITOCHONDRION