Physical Anthropology-- Cells

proteins

three-dimensional molecules that serve a wide variety of functions through their ability to bind to other molecules

nucleus

a structure (organelle) found in all eukaryotic cells. the nucleus contains DNA and RNA, among other things

DNA

the double-stranded molecule that contains the genetic code. DNA is a main component of chromosomes

RNA

a single-stranded molecule similar in structure to DNA

Three forms of RNA essential to protein synthesis

• messenger RNA (mRNA)

• transfer RNA (tRNA)

• ribosomal RNA (rRNA)

protein synthesis

the manufacture of proteins; that is, the assembly of chains of amino acids into functional protein molecules. protein synthesis is directed by DNA

mitochondria

structures contained within the cytoplasm of eukaryotic cells that convert energy, derived from nutrients, that can be used by the cell. the cell’s engines

Ribosomes

structures composed of a form of RNA called ribosomal RNA (rRNA) and protein. ribosomes are found in a cell’s cytoplasm and are essential to the manufacture of proteins.

nucleotides

basic units of the DNA molecule, composed of a sugar, a phosphate, and one of four DNA bases

the 4 nitrogenous bases

• adenine (A)

• guanine (G)

• thymine (T)

• cytosine (C)

Which bases can pair with which?

• A can pair only with T

• G can pair only with C

(This specificity is absolutely essential to the DNA molecule’s ability to replicate)

enzymes

specialized proteins that initiate and direct chemical reactions in the body

complementary

in genetics, referring to the fact that DNA bases form pairs (called base pairs) in a precise manner. for example, adenine (A) can only bond with thymine (T). these two bases are said to be complementary because one requires the other to form a complete DNA base pair

hemoglobin

a protein molecule that occurs in red blood cells and binds to oxygen molecules

hormones

substances (usually proteins) that are produced by specialized cells and that travel to other parts of the body, where they influence chemical reactions and regulate various cellular functions

amino acids

small molecules that are the components of proteins

Why is RNA different from DNA?

1. It’s single-stranded

2. It contains a different type of sugar

3. It contains the base uracil as a substitute for the DNA base thymine

messenger RNA (mRNA)

a form of RNA that’s assembled on a sequence of DNA bases.

it carries the DNA code to the ribosome during protein synthesis

Transcription

the formation of RNA, in which the DNA code is being copied, or transcribed

codons

triplets of messenger RNA bases that code for specific amino acids during protein synthesis

transfer RNA (tRNA)

a type of RNA that binds to specific amino acids and transports them to the ribosome during protein synthesis

mutation

a change in DNA.

the term can refer to changes in DNA bases (specifically called point mutations) as well as to changes in chromosome number and/or structure.

gene

a sequence of DNA bases that specifies the order of amino acids in an entire protein, a portion of a protein, or any functional product, such as RNA.

a gene may be composed of thousands of DNA bases

genome

the entire genetic makeup of an individual or species.

in humans, it’s estimated that the human genome comprises about 3 billion DNA bases

noncoding DNA

DNA that does not direct the production of proteins.

however, such DNA segments produce thousands of molecules (e.g., RNA) that are involved in gene regulation.

Exons

segments of genes that are transcribed and are involved in protein synthesis. (the prefix ex denotes that these segments are expressed

Introns

segments of genes that are initially transcribed and then deleted. because introns are not expressed, they aren’t involved in protein synthesis

what is meant by expressed?

by expressed we mean that the DNA sequence is actually making a product

regulatory genes

genes that influence the activity of other genes

regulatory genes direct embryonic development and are involved in physiological processes throughout life. they are critically important to the evolutionary process

homeobox genes

an evolutionarily ancient family of regulatory genes that directs the development of the overall body plan and the segmentation of body tissues.

there are at least 20 families of homeobox genes

sickle-cell anemia

a severe inherited hemoglobin disorder in which red blood cells collapse when deprived of oxygen.

it results from inheriting two copies of a mutant allele. the type of mutation that produces the sickle-cell allele is a point mutation

point mutation

a change in one of the four DNA bases

chromosomes

discrete structures composed of DNA and proteins found only in the nuclei of cells

what is the number of chromosomes in the somatic cells of humans?

46 (23 from mom, 23 from dad)

autosomes

all chromosomes except the sex chromosomes

all normal human somatic cells have _____ pairs of autosomes

22

sex chromosomes

in mammals, the X and Y chromosomes

all normal human somatic cells have ____ pairs of sex chromosomes

1

alleles

alternate forms of a gene.

alleles occur at the same locus on paired chromosomes and thus govern the same trait, but because they’re different, their action may result in different expressions of that trait.

locus

the position or location on a chromosome where a given gene occurs

mitosis

simple cell division; the process by which somatic cells divide to produce two identical daughter cells

meiosis

cell division in specialized cells in ovaries and testes.

meiosis involves two divisions and results in four daughter cells, each containing only half the original number of chromosomes. these cells can develop into gametes

recombination

the exchange of genetic material between paired chromosomes during meiosis; also called crossing over

Sexual reproduction and meiosis are of major evolutionary importance because they contribute to the role of _______________ in populations

natural selection