BIO 183 Study Guide 1 Exam 1

What are the properties of water that make life on earth possible?

• Water is a small polar molecule

• Forms hydrogen bonds with itself and compounds in solution (“Universal Solvent”)

• High surface tension and adhesion: Water molecules stick to each other (cohesion) and to other surfaces (adhesion). These properties help with things like water transport in plants (capillary action in xylem) and maintaining continuous columns of water.

• High specific heat and heat of vaporization: Water can absorb a lot of heat without changing temperature much. It takes a lot of energy for water to evaporate. This makes evaporative cooling (like sweating) effective at regulating body temperature.

• Lends stability to aquatic and  internal organismal environments

What is special about carbon atoms and their role in biological molecules?

• Carbon – key component of macromolecules

• Carbon is unique

• Each carbon has four electrons in the outer shell

• It forms up to four covalent bonds to “fill” the outer shell maximum of 8 e-

• Carbon's bonding flexibility and stability make it uniquely suited to build the complex, dynamic molecules that life depends on.

Dehydration reaction (condensation)

Water is released. An –OH from one molecule and an –H from another combine to form H₂O, and a new covalent bond forms between the two molecules. This is how smaller units (like monomers) are joined together to build polymers.

Hydrolysis reaction

Water is used (added). A water molecule is split into –OH and –H, which are added to the molecules, causing a covalent bond to break. This is how polymers are broken down into monomers.

What is meant by the statement that glucose is a dynamic molecule?

It can convert between forms.  It can change between ring and linear conformations.

What is the main difference between alpha and beta glucose, and what results when these two  forms of glucose are joined together in a polymer?

 Different configurations of the OH group on carbon 1 and its interaction with the OH group on carbon 2.

α-glucose: the –OH on carbon 1 points downward (below the plane of the ring).

β-glucose: the –OH on carbon 1 points upward (above the plane of the ring).

What types of linkages join carbohydrates?

glycosidic linkages

How does a dehydration reaction differ from hydrolysis in terms of water and bond formation?

• Dehydration reaction (condensation): a water molecule is removed. When water is taken away, a new covalent bond forms between two molecules (like linking two monosaccharides together). This is how larger molecules—polymers—are built.

• Hydrolysis: a water molecule is added. The added water breaks a covalent bond, splitting a large molecule into smaller units (like breaking a disaccharide into two monosaccharides).

Why are lipids considered hydrophobic?

Lipids are considered hydrophobic because they consist mostly of hydrocarbons, which form nonpolar covalent bonds. They don’t mix well with water.

Which specific chemical bonds contribute to lipids being considered hydrophobic?

Most lipids are made mostly of long hydrocarbon chains, which contain nonpolar carbon–carbon (C–C) and carbon–hydrogen (C–H) bonds. These bonds share electrons fairly evenly, so they don’t have partial charges. Water, on the other hand, is polar and interacts best with charged or polar substances through hydrogen bonding.

How do the double bonds in unsaturated fatty acids affect the physical state of the lipid at  room temperature compared to saturated fatty acids?

Unsaturated fats have double bonds that put bends in the fat chains. Those bends keep the fats from packing tightly, so they stay liquid at room temperature (like oil).

Saturated fats don’t have double bonds, so their chains are straight and pack together easily. That’s why they’re usually solid at room temperature (like butter).

Describe the structure of a phospholipid.

A phospholipid has a phosphate “head” and two fatty acid “tails.”

• The head contains a phosphate group and is hydrophilic (it likes water).

• The tails are long hydrocarbon chains and are hydrophobic (they avoid water).

Fatty Acids

Long chains of carbon and hydrogen with a carboxyl group on one end. They are the building blocks of many other lipids.

Triglycerides (fats and oils)

Made of one glycerol molecule attached to three fatty acids. Their main job is long-term energy storage.

Phosoholipids

Made of glycerol, two fatty acids, and a phosphate group. They have a water-loving head and water-fearing tails, so they form cell membranes.

Steriods

Have a completely different structure—four fused carbon rings. They are used as hormones (like estrogen and testosterone) or for membrane structure (like cholesterol).

What types of linkage joins the components of triglycerides?

Ester Bond

What structural feature of trans fats makes them different from naturally occurring cis  unsaturated fats?

• Cis unsaturated fats have hydrogen atoms on the same side of the carbon–carbon double bond. This creates a bend (kink) in the fatty acid chain.

• Trans fats have hydrogen atoms on opposite sides of the double bond. This makes the chain straighter, more like a saturated fat.

So structurally, trans fats lack the natural bend found in cis fats, which is why they pack more tightly and behave more like saturated fats.

Explain why phospholipids are described as "amphipathic"

It’s called amphipathic because it has both parts: one end that likes water and one end that doesn’t. This is why phospholipids naturally form cell membranes, with the heads facing water and the tails tucked away from it.

How does the sequence of amino acids (primary structure) ultimately dictate the function of a protein?  

The sequence of amino acids in a protein (its primary structure) determines how the chain folds into 3D shapes.

• Different amino acids have different chemical properties (some are hydrophobic, some are charged, etc.).

• These properties cause the chain to fold, twist, and interact in specific ways, forming the protein’s secondary, tertiary, and quaternary structures.

• The final 3D shape determines the protein’s function, because a protein can only do its job if it has the right shape (like an enzyme fitting its substrate or a receptor binding a signal molecule).

What is an alpha helix?  

a secondary structure characterized by a segment of the polypeptide chain that is repeatedly coiled into a spiral/helical shape

What is a beta sheet?  

a secondary structure consisting of segments of the polypeptide chain that are folded or pleated back and forth