Cch n gin nht l ly mt s lng ln cc vi khun khc nhau t nhiu mi trng
khc nhau v xem con no pht trin trong mt mi trng m c mt lng nh
benzen. Nu c bt c th g pht trin, sau bn xem liu n s tng trng nng
cao hn ca benzen cho n khi bn c mt loi tng trng nng cao
Pairs of nitrogenous bases, one from each strand, connect the polynucleotide
chains with hydrogen bonds.
Most DNA molecules have thousands to millions of base pairs.
Because of their shapes, only some bases are compatible with each other.
Adenine (A) alwa
Because the atoms in both the nitrogenous base and the sugar are numbered, the
sugar atoms have a prime after the number to distinguish them.
Thus, the second carbon in the sugar ring is the 2 (2 prime) carbon and the
carbon that sticks up from the ring i
While DNA encodes the information that programs all the cells activities, it is
not directly involved in the day-to-day operations of the cell.
Proteins are responsible for implementing the instructions contained in DNA.
Each gene along a DNA molecule dir
Chaperonins do not specify the final structure of a polypeptide but rather work
to segregate and protect the polypeptide while it folds spontaneously.
At present, scientists use X-ray crystallography to determine protein
This technique requi
It consists of four polypeptide subunits: two alpha and two beta chains.
Both types of subunits consist primarily of alpha-helical secondary structure.
Each subunit has a nonpeptide heme component with an iron atom that binds
What are the key fact
the protein that carries oxygen in red blood cells, can cause sickle-cell disease,
an inherited blood disorder.
The abnormal hemoglobins crystallize, deforming the red blood cells into a
sickle shape and clogging capillaries.
Most proteins have segments o
It is the order of amino acids that determines what the three-dimensional
conformation of the protein will be.
A proteins specific conformation determines its function.
When a cell synthesizes a polypeptide, the chain generally folds spontaneously
Note that all amino acids have carboxyl and amino groups. The terms acidic
and basic in this context refer only to these groups in the R groups.
Amino acids are joined together when a dehydration reaction removes a
hydroxyl group from the carboxyl end of
Most important, protein enzymes function as catalysts in cells, regulating
metabolism by selectively accelerating chemical reactions without being
Humans have tens of thousands of different proteins, each with a specific
structure and function.
When phospholipids are added to water, they self-assemble into assemblages
with the hydrophobic tails pointing toward the interior.
This type of structure is called a micelle.
Phospholipids are arranged as a bilayer at the surface of a cell.
Again, the hy
The phrase hydrogenated vegetable oils on food labels means that unsaturated
fats have been synthetically converted to saturated fats by the addition of
Peanut butter and margarine are hydrogenated to prevent lipids from
separating out as oil.
Although fats are not strictly polymers, they are large molecules assembled
from smaller molecules by dehydration reactions.
A fat is constructed from two kinds of smaller molecules: glycerol and fatty
Glycerol is a three-carbon alcohol with a hydr
In plant cell walls, parallel cellulose molecules held together in this way are
grouped into units called microfibrils, which form strong building materials
for plants (and for humans, as lumber).
The enzymes that digest starch by hydrolyzing its alpha li
Starch is a storage polysaccharide composed entirely of glucose monomers.
Most of these monomers are joined by 14 linkages (number 1 carbon to
number 4 carbon) between the glucose molecules.
The simplest form of starch, amylose, is unbranched and forms a
Monosaccharides have a carbonyl group (>C=O) and multiple hydroxyl groups
Depending on the location of the carbonyl group, the sugar is an aldose or a
Most names for sugars end in -ose.
Glucose, an aldose, and fructose, a ketose, are structu
In hydrolysis, bonds are broken by the addition of water molecules. A hydrogen
atom attaches to one monomer, and a hydroxyl group attaches to the
Our food is taken in as organic polymers that are too large for our cells to
Chapter 5: The Structure and Function of Macromolecules
Overview: The Molecules of Life
Within cells, small organic molecules are joined together to form larger
Four major classes: