BIOL 1710: Chapter 5 Answers

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What functional feature(s) does the phosphate group contribute to the structure of a phospholipid?

A place to attach another small charged molecule and provides a negative charge to interact with water.

The following are the functional characteristics of phospholipids that are due to the phosphate group:

  1. Negative charge to interact with water.
  2. A place to attach another small molecule.

The phosphate group has four oxygen atoms linked to one phosphorus atom. This molecule has a net negative charge of -3. The phosphate added polarity to the phospholipid head by donating an electron in the form of a negative charge. Phosphate also acts as a junction where other small molecules, such as alcohol and serine, can be connected.

Defining Characteristics of Phospholipids

Phospholipids are components of the cell membrane, which is the outermost layer of animal cells. They’re made up of fatty acid chains linked to a glycerol backbone, just like fats. Phosphatides have two fatty acids instead of three in triglycerides, which assist in the formation of a diacylglycerol. A modified phosphate group occupies the third carbon as well.

However, the term “phospholipid” does not refer only to a phosphate group attached to a diacylglycerol. This would be classified as a phosphatidate (diacylglycerol 3-phosphate), which is used in the synthesis of phospholipids. The phosphate group should be modified by alcohol in order for it to qualify as a phospholipid. Phosphatidylcholine and phosphatidylserine are two important plasma membrane phospholipids.

A phospholipid is a lipid that has two fatty acids and a modified phosphate group linked to a glycerol backbone. The phosphate may be flavored or charged using polar or charged chemical compounds. Here are shown two chemical groups that can be used to modify the phosphate, choline and serine. Choline and serine attach to the phosphorus atom at R, which is indicated by the green hydroxyl group, via the hydroxyl group shown in green.

Structure of a Phospholipid Molecule

A phospholipid is a molecule with two hydrophobic and two hydrophilic regions. The phosphate group on one end, known as the “head,” is charged negatively, making it polar and hydrophilic, or “water-loving.” Because of this charge, the phosphate heads are drawn to the water molecules in their surrounding environment.

The tails are long chains of hydrophobic lipids that are uncharged, nonpolar, and hydrophobic (or “water afraid”). Water repels and is repelled by a hydrophobic molecule. Some lipid tails include saturated fatty acids while others have unsaturated fatty acids. This mixture improves the fluidity of the tail signals that are in continual motion.

A dehydration reaction (or condensation reaction) is the process in which
water molecules are produced as a polymer is formed from monomers
The four main categories of large biological molecules present in living systems are
proteins, nucleic acids, carbohydrates, and lipids
Sucrose is formed when glucose is joined to fructose by a(n)
glycosidic linkage (joins simple sugars to form polysaccharides)
Plant cell walls consist mainly of
cannot be hydrolyzed any further
A simple sugar is composed of equal parts carbon and water, which gave rise to the general name of any sugar as a
Lactose (the sugar in milk) is a ____, because it can be split into two monosaccharides
a carbohydrate that yields many monosaccharides when hydrolyzed
How many fatty acids are in a phospholipid?
What functional features does the phosphate group contribute to the structure of a phospholipid?
place to attach another small charged molecule, negative charge to interact with water
What holds phospholipids together in a bilayer formation?
hydrophilic and hydrophobic interactions with water
Which molecule is less soluble in water-a fat or a phospholipid? Why?
A fat molecule is less soluble in water because it has three non-polar fatty acids and no polar or charged head like a phospholipid has
The characteristic that all lipids have in common is that
none of them dissolves in water
Palm oil and coconut oil are more like animal fats than are other plant oils. Because they _____ than other plant oils, they may contribute to cardiovascular disease
contain fewer double bonds
Some regions of a polypeptide may coil or fold back on themselves. This is called _____, and the coils or folds are held in place by _____
secondary structure. . .hydrogen bonds
A hydrophobic amino acid R group (side group) would be found where in a protein?
on the inside of the folded chain, in the water
If you wanted to show the 3-dimensional shape of a protein, including all of the atoms composing it, you should use a
space-filling model
If you wanted to show the general shape of a protein, along with some important functional details such as folds and coils, you should use a
simplified diagram
If you wanted to show the 3-dimensional shape of a protein, including the backbone structure, folds, and coils, you should use a
ribbon model
If you wanted to show a generalized protein in which the focus is on the protein’s function rather than its structure, you should use a
simple shape
If you wanted to show the 3-dimensional shape of a protein by showing the amino acid side chains and their interactions, you should use a
wireframe model
The flow of genetic information in a cell goes from
DNA to RNA to protein
The building blocks or monomers of nucleic acid molecules are called
Which of the following categories includes all others in the list?
Which of the following statements concerning unsaturated fats is true?
They have double bonds in the carbon chains of their fatty acids
Give Examples of Lipids
Steroids (ex. chlosterol)
Lipids have _____ _____ in water.
low solubility.
Name four steroids
Vitamin D
An important component of animal cell membranes.
The primary female sex hormone, produced in ovaries.
The most abundant male sex produced in the testes.
Vitamin D
Aids in calcium and phosphate metabolism.
What is the structure of the phospholipid?
-A three carbon chain glycerol.
– Fatty Acids (2 tails)
-Phosphate group (negative charge) and attached to another charged molecule.
What functional features does the phosphate group contribute to the structure of a phospholipid?
It has a place to attach another small charged molecule and it has a negative charge to interact with water.
What holds phospholipids together in a bilayer formation?
Hydrophilic and hydrophobic interactions with water.
Which molecule is less soluble in water– a fat or a phospholipid? Why?
A fat molecule is less soluble in water because it has three non-polar fatty acids and no polar or charged head ike a phospholipid has.
The Characteristic that all lipids have in common is that _________.
None of them dissolve in water. Almost all covalent bonds in lipids are nonpolar, causing their solubility in water to be extremely low. Lipids are hydrophobic substances.
Hydrophobic substances like salad oil are
Nonpolar molecules that repel water molecules.
What cannot rapidly pass directly through the phospholipids of the plasma membrane?
Water, glucose, ions
Non-polar molecules are?
Hydrophobic, can ceoss easily cross a lipid bilayer, and no transport protein is required.
Polar molecules are?
Hydrophilic, has difficulty crossing a lipid bilayer, and requires a transport protein.
Ions (Na +, K+, etc) are?
Hydrophilic, have difficulty crossing a lipid bilayer, and requires a transport protein.
When molecules move down their concentration gradient, they move from where they are ______ to where they are _____.
high concentration, less concentrated.
Diffusion across a biological membrane is called _____.
passive transport
Which of the following factors does not affect membrane permeability?
The polarity of membrane phospholipids.
How are lipids distinguished from a sugar?
Lipids are mostly nonpolar.
What property of dishwashing liquid makes it useful to wash grease from pans?
Amphipathic nature
– Detergents form micelles around the grease which are then washed away becuase the polar head groups facing outward on the micelle are water-soluble.
Facilitated diffusion is a type of ____.
Passive transport.
Passive transport of water
Is the bursting of the cell.
The swelling of the plant cells.
During osmosis water diffuses across a selectively permeable membrane from the region of higher ____ concentration and lower ____ to the side with lower ____ concentration and higher ___ concentration.
free water, solute, free water, solute
A human cell placed into a hypertonic solution is likely to
lose water by osmosis.
When a person is dehydrated, his or her IV fluids should be what?
Isotonic, because either a hypertonic or hypotonic IV would damage red blood cells.
Transport CHANNELS do what?
– provide a continous path across the membrane.
– allow water molecules and small ions to flow quickly across the membrane.
Transport CARRIERS do what?
– transport primarily small polar organic molecules
– undergo a change in shape to transport solutes across the membrane.
Both Channels and Carriers do what?
– Are intergral membrane proteins
– Provide a hydrophilic path across the membrane
– Transport solutes down a concentration or electrochemical gradient.
The movement of glucose into a cell against a concentration gradient is most likely to be accomplished by what?
contransport of the glucose with a proton or sodium ion that was pumped across the membrane using the energy of ATP hydrolysis.
Active and passive transport of solutes across a membrane typically differ in what way?
Active transport always involves the utilization of cellular energy, whereas passive transport does not require cellular energy.
A type of active transport, where the energy available from an ion moving through a transport protein dow its electrochemical gradient is coupled with the movement of another solute through the same protein but against its concentration or electrochemical gradient.
Endocytosis moves materials ____ a cell via ______.
into, membranous vesicles
the cell is engulfing extracellular fluid.
When the cell engulfs a large particle.
What describes some aspect of exocytosis and endocytosis?
Both temporarily change the surface area of the plasma membrane.
– The fusion or budding of transport vesicles at the plasma membrane either adds or removes proteins and phospholipids, thus temporarily changing the surface area.
– requires fusion of vesicles with the plasma membrane.
– increases the surface area of the plasma membrane
– secretes large molecules out of the cell
– forms vesicles from inward folding of the plasma membrane
– decreases the surface area of the plasma membrane.
Both exocytosis and endocytosis
– requires cellular energy
– transported substances never physically cross the plasma membrane.
In what way do membranes vary among eukaryotic cells?
– Certain proteins are unique to each membrane.
According to the fluid mosaic model of membrane structure, proteins of the membrane are mostly
embedded in a lipid bilayer.
What factor would tend to increase membrane fluidity?
A greater proportion of unsaturated phospholipids.

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