Search Results

Peptide Bond Formation Animation

By: HWC, Views: 1555

During protein synthesis, peptide bonds link amino acids together in the order specified by DNA instructions. In this case, the first two amino acids in the protein are methionine and alanine. Here are ball-and-stick models of these amino acids. Peptide bond formation is a type of condensatio...

Secondary and tertiary levels of protein structure Animation

By: HWC, Views: 1649

Amino acid sequence dictates a protein's final shape. The presence of certain amino acids favors a pattern of hydrogen bonding that causes part of the polypeptide chain to coil and twist into an alpha helix. The presence of other amino acids enables hydrogen bonding between strand like re...

DNA close up Animation

By: HWC, Views: 1665

A section from a DNA double helix The backbone of each DNA strand consists of alternating deoxyribose sugars and phosphate groups. The two strands run in opposite directions. One runs from the 5' to 3' direction, the other in the 3' to 5' direction. Think of the deoxyribose units o...

Evolutionary tree of life Animation

By: HWC, Views: 1394

An evolutionary tree of life that reflects mainstream thinking about the connections among major lineages (bya = billions of years ago, mya = millions of years ago). By about 3.8 billion years ago, chemical and molecular evolution had produced the first living cells. The first major divergenc...

Generalized life cycles for plants and animals Animation

By: HWC, Views: 1792

But the life cycles of plants and animals differ in their details. In animals, a multicelled diploid stage gives rise to single-celled haploid gametes, the eggs and sperm. These gametes combine at fertilization to form a diploid zygote, which grows and develops into a new multicelled animal...

Origin of organelles Animation

By: HWC, Views: 1385

Possible origins of the nucleus and other organelles. Some prokaryotic cells have infoldings of their plasma membrane. These infoldings may have served as channels from the cytoplasm to the cell surface. These membranous folds may have evolved into the endoplasmic reticulum and the nuclear e...

Miller's reaction chamber experiment Animation

By: HWC, Views: 1320

A simple diagram of Stanley Miller and Harold Urey's experimental apparatus. The lower portion of the apparatus was filled with water. The upper portion was filled with a mixture of gases that simulated the earth's early atmosphere. Examples are methane, ammonia, hydrogen and carbon dioxide. ...

Random alignment at Metaphase I Animation

By: HWC, Views: 2141

Possible outcomes of random alignment at metaphase I. In this example, three types of chromosomes are labeled 1, 2, and 3. Maternal chromosomes are dark blue; paternal ones are light blue. Suppose that at metaphase I all the maternal chromosomes became attached to one spindle pole and all the ...

Carbon fixing adaptations Animation

By: HWC, Views: 1811

Different plants trap carbon by different pathways. Most C3 plants evolved in moist, temperate zones. On hot dry days they close their stomata to conserve water and oxygen accumulates. Under these circumstances, the enzyme rubisco uses oxygen in an inefficient reaction that competes with t...