Transcript Cell Metabolism - s3.amazonaws.com

Cell Metabolism
Chapter 4
Lisa Ochs RN, MSN 2008
Metabolism
• The chemical reactions that occur in the body
• All energy and material transformations that occur
within living cells
• Anabolism
– Reactions that build more complex substances
from simpler ones; requires ATP
• Catabolism
– Reactions that break down complex substances;
releases ATP
Carbohydrates
• Found in all the best food- bread, potatoes,
pasta and sweets
• Organic compounds composed of carbon (C),
hydrogen (H), and oxygen (O)
• Classified according to size
• Shorter chains are called sugars, longer chains
are called starches
Monosaccharides
• Sugars that contain 3-6 carbons
• Glucose, fructose and galactose
• Glucose is the most important source of
energy
Disaccharides
• Double sugars
• Formed when 2 monosaccharides are joined
together
• Include sucrose, maltose and lactose
• Must be broken down into monosaccharides
before they can be used by the body
• Sucrose
Polysaccharides
• Many glucose molecules linked together
either in straight or branching chains
• Important polysaccharides include plant
starch, animal starch and cellulose
• Glycogen- highly branched chains; in humans,
glucose is stored as glycogen (in the liver and
muscles); it is released and converted into
glucose when blood glucose levels drop
Uses of glucose…
• Glucose is used by the body in 3 ways
– Burned immediately as fuel for energy
– Stored as glycogen and used at a later time
– Stored as fat and used at a later time
Breaking down glucose…
• Glucose can be broken down under 2
conditions:
– In the presence of oxygen- aerobic catabolism
– In the absence of oxygen- anaerobic catabolism
Breakdown of glucose…
• Anaerobic
– Glucose is broken down in a series of chemical
reactions that result in the production of lactic
acid
– Called glycolysis; occurs in cytoplasm
– Produces only a small amount of energy (most of
the energy remains in the lactic acid and the body
is unable to use it)
Breakdown of glucose…
• Aerobic
– Glucose is completely broken down to form CO2,
water and ATP
– Occurs in the mitochondria (uses enzymes found
in the mitochondria- remember??)
– Since the glucose is completely broken down, a
large amount of ATP is released
Aerobic breakdown of glucose…
•
•
•
•
Three important points…
1. Requires oxygen
2. Releases a large amount of energy (ATP)
3. If oxygen is not available, the glucose will be
converted into lactic acid (can be potentially
life-threatening)
Figure 4-3 Breakdown of glucose. A, Anaerobic: to lactic acid. B, Aerobic: to carbon dioxide, water, and ATP.
Elsevier items and derived items © 2007, 2003, 2000 by Saunders, an imprint of Elsevier Inc.
Making glucose…
• Cells can not only breakdown glucose, they
can also synthesize (make) glucose from noncarbohydrate sources (especially proteins)
• This process is called gluconeogenesis
Diabetic patients
• Glucose breakdown/ synthesis are especially
important to diabetics
• Insulin is needed to transport the glucose into
the cell (facilitated diffusion); without insulin,
the cells cannot use the glucose for energy
• Lack of insulin causes gluconeogenesis of
proteins; but the cells are unable to use the
glucose, so it accumulates in the blood
Diabetic patients
• Drugs used to treat diabetes work by:
– Increasing the uptake of glucose by the cells
– Suppressing the gluconeogenesis in the liver
– Both of these work to lower blood glucose levels
Lipids
• Organic compounds commonly called fats and
oils
– Fats are solid at room temperature
– Oils are liquid at room temperature
• Most common are triglycerides, phospholipids
and steroids
Lipids
• The building blocks of lipids
– Fatty acids
– Glycerol
• Triglycerides
– 3 long fatty acid chains attached to glycerol
• Phospholipids
– Phosphorus group attaches to glycerol
• Steroid
– Important steroid in the body- cholesterol; can be
synthesized by the liver; helps synthesize vitamin D and sex
hormones
Use of lipids…
• Source of energy for the body
• Component of cell membranes and myelin
sheaths
• Synthesis of steroids
• Can also be stored long term as adipose tissue
and deposited in blood vessels (athersclerosis)
Metabolism of lipids…
• Can be broken down to release stored energy
• Long fatty acid chains must be broken into
smaller pieces
• Large amount of energy released when lipids
are burned for energy (more than glucose)
• Excess fat is stored as adipose tissue
Proteins
• The most abundant organic matter in the
body
• Participate in nearly all functions of the body
• Found as enzymes, which are in almost all
chemical reactions
Amino Acids
• Building blocks of proteins- about 20 amino
acids used in the body
• Can be taken in through food (lean meat, milk,
eggs etc.) or synthesized by the body
• Essential amino acids (must be taken in
through diet)
• Nonessential amino acids (can be synthesized
by the liver)
Amino Acids
•Composed of carbon, hydrogen and oxygen
(like carbs and lipids) as well as nitrogen
•Amino acids have an amine group (NH2) at one
end and an acid group (COOH) at the other end
•Peptide bonds are formed when the amine
group of one joins with the acid group of
another
Peptides
•A peptide is formed when several amino acids
are joined together by peptide bonds
•A polypeptide is formed when many amino
acids are joined together
•Proteins are very large polypeptides (most are
composed of more than one polypeptide chain)
Uses of proteins…
• Synthesis of several substances including
hormones, enzymes, antibodies, plasma,
hemoglobin and cell membrane
• Can be broken down and used for energy (not
the preferred method)
• Can be broken down and converted to glucose
(gluconeogenesis)
Protein Breakdown
•The nitrogen part of the amino acid must be
recycled or excreted
•Most nitrogen is recycled to produce more
amino acids
•Some nitrogen is converted to urea by the liver
and excreted by the kidneys
•Blood Urea Nitrogen (BUN)- blood test used to
assess amount of urea in the blood
Protein Breakdown
•Ammonia (NH3) is a by-product of protein
breakdown (usually in the intestines)
•Usually removed from the blood by the liver
and converted to urea, which is excreted by the
kidneys
•High ammonia levels are toxic to brain cells;
results in hepatic encephalopathy
Formation and
excretion of urea
Protein Synthesis & DNA
• Proteins are crucial to all body functions
• Protein synthesis involves the precise
arrangement of amino acids in specific
sequences
• The pattern of assembly is coded and stored
within the DNA (deoxyribonucleic acid)found in the nucleus
• DNA is a code for the structure of proteins
DNA Structure
• DNA is a nucleic acid- composed of smaller
units called nucleotides
• Nucleotides are composed of a sugar, a
phosphate group and a base
• Joined together in long strands- two strands
are arranged in a “twisted ladder” formation
(the double helix) to form DNA
DNA Structure
•The sides of the ladder are
composed of sugar-phosphate
molecules
•The rungs of the ladder are
composed of bases- one base
on each side
DNA Structure
•The bases that make up the rungs include:
–Adenine
–Cytosine
–Guanine
–Thymine
•Bases have a specific arrangement, each base
combines specifically with another base- this is
called base-pairing
The Genetic Code
• The protein-synthesis code for the cell is
located along one strand of DNA (one side of
the ladder)
• These codes are arranged in units called
genes, so it is termed the genetic code
The Genetic Code
Reading the code
–Read vertically along the sides of the ladder; read in
groups of three, called base-sequencing
Copying the code
–Since DNA does not leave the nucleus, ribonucleic acid
(RNA) copies the code and delivers it to the ribosomes
(where protein synthesis occurs). This process of
copying is called transcription
Steps in protein synthesis…
• DNA and RNA control protein synthesis
• 5 steps involved
1. Base sequences are copied (transcription)
2. The mRNA carries it to the ribosomes in the
cytoplasm
3. The code on the mRNA tells specific amino
acids where to bind
4. The amino acids are now lined up correctly
and peptide bonds form
5. The protein chain is finished and a complete
new protein is formed