Chapter 4: Genetics And Cellular Function

Dominant

(1. Pertaining to a genetic table that is phenotypically expressed in the presence of any other allele. 2. Pertaining to a trait that results from a ___ allele.)

Growth factors

(A chemical messenger that stimulates mitosis and differentiation of target cells that have receptors for it; important in such processes as fetal development, tissue maintenance and repair, and hemopoiesis; sometimes a contributing factor in cancer.)

Chromosomes

(A complex of DNA and protein carrying the genetic material of a cell's nucleus. Normally there are 46 chromosomes in the nucleus of each cell except germ cells.)

Golgi vesicles

(A membrane-bounded vesicle pinched from the Golgi complex, containing its chemical product; may be retained in the cell as a lysosome or become a secretory vesicle that releases the product by exocytosis.)

Golgi complex

(An organelle composed of several parallel cisternae, somewhat like a stack of saucers, that modifies and packages newly synthesized proteins and synthesizes carbohydrates.)

Autosomes

(Any chromosome except the sex chromosomes. Genes on the ___ are inherited without regard to the sex of the individual.)

Alleles

(Any of the alternative forms that one gene can take, such as dominant and recessive alleles.)

Distinctive base sequences

(Often TATATA or TATAAA) informs the polymerase where to begin.

Gene locus

(The site on a chromosome where a given gene is located.)

DNA structure

(a) A molecular space-filling model of DNA giving some impression of its molecular geometry. (b) The "spiral staircase" structure. The two sugar-phosphate backbones twine around each other while complementary bases (colored bars) face each other on the inside of the double helix. (c) A small segment of DNA showing the composition of the backbone and complementary pairing of the nitrogenous bases.

Carriers

- (1. A protein in a cellular membrane that performs carrier-mediated transport. 2. A person who is heterozygous for a recessive allele and does not exhibit the associated phenotype, but may transmit this allele to his or her children; for example, a ___ for sickle-cell disease.) - They will always be heterozygous.

Homologous chromosomes

- (1. Having the same embryonic or evolutionary origin but not necessarily the same function, such as the scrotum and labia majora. 2. Pertaining to two chromosomes with identical structures and gene loci but not necessarily identical alleles; each member of the pair is inherited from a different parent.) - Chromosomes occur in 23 pairs, the two members of each pair is called this.

Somatic cells

- (1. Pertaining to the body as a whole. 2. Pertaining to the skin, bones, and skeletal muscles as opposed to the viscera. 3. Pertaining to cells other than germ cells.) - Basically, all the cells in the body except those involved with reproduction.

Mitosis

- (A form of cell division in which a cell divides once and produces two genetically identical daughter cells; sometimes used to refer only to the division of the genetic material or nucleus and not to include cytokinesis, the subsequent division of the cytoplasm.) The functions of cell division: - Development of an individual, composed of some 50 trillion cells, from a one-celled fertilized egg; - Growth of all tissues and organs after birth; - Replacement of cells that die; and - Repair of damaged tissues.

Germ cells

- (A gamete or any precursor cell destined to become a gamete.) - Sperm and eggs, and cells on their way to becoming sperm and eggs are called this.

Genome

- (All the genes of one individual, estimated at 20,000 to 25,000 genes in humans.) - The 46 human chromosomes come in two sets of 23 each, one set from each parent. - Except for 2 sex chromosomes, the chromosomes of each pair have the same genes, but may have different versions of a given gene (alleles). - All the DNA, both coding and noncoding in one 23-chromosome set from one parent.

Genes

- (An information-containing segment of DNA that codes for the production of a molecule of RNA, which in most cases goes to play a role in the synthesis of one or more proteins.) - The amino acid sequence of a protein is determined by a nucleotide sequence in the DNA. - Only code for proteins. other cell products like glycogen, nucleic acids or lipods are produced by enzymatic reactions, and enzymes are proteins encoded by genes. - Some genes produce only RNA molecules and not proteins. - Some genes overlap each other, so some segments of DNA belong to two different genes. - An information-containing segment of DNA that codes for the production of a molecule of RNA, which in most cases goes on to play a role in the synthesis of one or more proteins. - In a given cell, some genes are never turned on. - Genes can be turned on or off from hour to hour depending on whether or not their products are needed. - A hormone can turn a gene on or off. - There are several ways to turn genes on.

Nucleotide

- (An organic molecule composed of a nitrogenous base, a monosaccharide, and a phosphate group; the monomer of a nucleic acid.) - An organic molecule composed of a nitrogenous base (a single- or double-ringed), a monosaccharide (a sugar - ribose or deoxyribose), and a phosphate group; the monomer of a nucleic acid. - The amino acid sequence of a protein is determined by this sequence in the DNA.

Nitrogenous base

- (An organic molecule with a single or double carbon-nitrogen ring that forms one of the building blocks of ATP, other nucleotides, and nucleic acids; the basis of the genetic code.) - An organic base that contains nitrogen, such as a purine or pyrimidine; a subunit of a nucleotide in DNA and RNA.

Mutations

- (Any change in the structure of a chromosome or a DNA molecule, often resulting in a change or organismal structure or function.) - Changes in DNA structure; can result from replication errors or from environmental factors such as radiation, chemicals, and viruses.

Chromatin

- (Filamentous material in the interphase nucleus, composed of DNA and associated proteins.) - A fine filamentous DNA material complexed with proteins. - Occurs as 46 chromosomes in most cells. - 6 feet long thread packed in cell nucleus of 5 μm diameter. - In nondividing cells, it is so slender it cannot be seen with light microscope. - Granular appearance under electron microscope.

Homozygous

- (Having identical alleles at the same gene locus of two homologous chromosomes.) - Individuals with two identical alleles, such as CC or cc.

Heterozygous

- (Having nonidentical alleles at the same gene locus of two homologous chromosomes.) - When the homologous chromosomes have different alleles for that gene (Cc).

Haploid

- (In humans, having 23 unpaired chromosomes instead of the usual 46 chromosomes in homologous pairs; in any organism or cell, having half the normal diploid number of chromosomes for that species.) - (i.e. Sperm and egg cells).

Genotype

- (The pair of alleles possessed by an individual at one gene locus on a pair of homologous chromosomes; strongly influences the individual's phenotype for a given trait.) - The alleles an individual possesses for a particular trait.

Translation

- (The process of enzymatically reading an mRNA molecule and synthesizing the protein encoded in its nucleotide sequence.) - The step from mRNA to protein; occurs in the cytoplasm, but 10% to 15% of proteins are synthesized in the nucleus. - The process of enzymatically reading an mRNA molecule and synthesizing the protein encoded in its nucleotide sequence. - It occurs in three steps called initiation, elongation, and termination. - The conversion of nucleotide sequences into amino acid sequences. Steps: - tRNA anticodon binds to a complementary mRNA codon. - Ribosome binds mRNA. - tRNA released from ribosome available to pick up another amino acid. - A new amino acid is linked to the growing peptide chain. - Needed for the initiation of translation: methionine, mRNA, start codon AUG, initiator tRNA, ribosomal subunits. - During the process of translation, the three-nucleotide sequence (AUG) serves as a code for methionin and also as a start codon that signals the beginning of a new protein. the three nucleotide sequences (UAG, UGA or UAA) terminate the process and are called stop codons. - Requires ribosomes - Anticodons - Polyribosomes - Creates primary protein structure - Synthesis of an amino acid chain - Can include rough ER - The three letter sequences being "read" during translation is a codon.

Codon

- A 3-base sequence in mRNA. - The genetic code is expressed in terms of these. - It's carried to a ribosome where the code is translated into a sequence of amino acids.

DNA

- A cell's hereditary matter; the repository of our gene. - It contains a sugar called deoxyribose, it contains nitrogenous bases A, T, C, G; it consists of two nucleotide chains (double helix); it functions in the nucleus; it codes for synthesis of RNA and protein. - A polymer of nucleotides, each of which consists of a phosphate, a sugar, and a single or double-ringed nitrogenous base. - The nitrogenous bases face the inside and hold the to backbones together with hydrogen bonds. - Each sidepiece is a sugar-phosphate backbone composed of phosphate groups alternating with the sugar deoxyribose. - In a molecule of this, the nitrogenous bases adenine and thymine form two hydrogen bonds with each other. - It may contain thymine. - The longest chain of nucleotides.

Ribosomes

- A granule found free in the cytoplasm or attached to the rough endoplasmic reticulum, composed of ribosomal RNA and enzymes; specialized to read the nucleotide sequence of messenger RNA and assemble a corresponding sequence of amino acids to make a protein. - Each ribosome consists of a small and a large subunit in their inacitve form that come together only when translating mRNaA. - Each ribosome is composed of several enzymes and ribosomal RNA (rRNA) molecules. - Each ribosome has three pockets that serve as binging sites for tRNA (A, P and E sites). - They are found in the cytosol and on the outside of the rough ER and nuclear envelope.

Pleiotropy

- A phenomenon in which one gene produces multiple phenotypic effects. - An example is alkaptonuria, a disorder resulting from mutation on chromosome 3 that blocks the breakdown of tyrosine - An example is sickle-cell disease.

tRNA

- A relatively small RNA whose job is to bind a free amino acid in the cytosol and deliver it to the ribosome to be added to a growing protein chain. tRNA is a single-stranded molecule that turns back and coils on itself to form an angular L shape. - It has a section that binds to a codon - Bound to an amino acid - Binds to the large subunit of ribosome - Carries amino acids to the ribosomes. - Contains anticodons. - Located only in the cytoplasm. - In response to the base sequence AUG contributes methionine to the amino acid chain. - Structure described as being short, single-stranded chain of nucleotides with occasional areas of intramolecular (base-base) binding.

Base triplet

- A sequence of 3 DNA nucleotides that stands for 1 amino acid.

Centrioles

- A short cylindrical assembly of microtubules arranged in nine groups of three microtubules each. - Short cylindrical bodies, each composed of a circle of 9 triplets of microtubules. - Form mitotic spindle during cell division; unpaired ___ form basal bodies of cilia and flagella.

Genetic code

- A system that enables these 4 nucleotides to code for the amino acid sequences of all proteins. - A system that enables 4 DNA nucleotides to dictate the amino acid sequences of millions of proteins.

RNA polymerase

- An enzyme that binds to the DNA and assembles the RNA. ___ opens up the DNA helix about 17 base pairs at a time. It reads the bases from one strand of the DNA and makes corresponding RNA. Where it finds a C on the DNA, it adds a G to the RNA; where it finds an A, it adds a U; and so forth. The enzyme then rewinds the DNA helix behind it. - Another ___ may be transcribed by several polymerase molecules at once, and numerous copies of the same RNA are made. - At the end of the gene sequence is a base sequence that serves as a terminator, which signals the polymerase to stop.

Phenotype

- An observable trait. - An allele is expressed if it shows in the ___ of an individual. - An organism's physical appearance, or visible traits.

Base pairs

- Any of the pairs formed between complimentary bases in the two nucleotide chains of DNA, such as A-T and C-G (DNA) A-U and C-G (RNA). - A given purine cannot arbitrarily bind to just any pyrimidine. Adenine and thymine form 2 hydrogen bonds with each other, and guanine and cytosine form 3 hydrogen bonds. Therefore, where there is an A on one backbone, there is normally a T across from it, and every C is normally paired with a G.

Chaperone

- As a new protein is assembled by a ribosome, it is often bound by an older protein. It guides the new protein in folding into the proper shape and helps to prevent improper associations between different proteins. As in the colloquial sense of the word, a ___ is an older protein that escorts and regulates the behavior of the "youngsters." - They are also known as stress proteins or heat shock proteins. - They aid a newly synthesized protein in folding to its proper shape. - They help prevent improper associations between different proteins.

Prophase

- At the outset of mitosis, the chromosomes shorten and thicken, eventually coiling into compact rods that are easier to distribute to daughter cells than the long, delicate chromatin of interphase. There are 46 chromosomes, 2 chromatids per chromosome, and 1 molecule of DNA per chromatid. The nuclear envelope disintegrates during this phase and releases the chromosomes into the cytosol. - Chromosomes condense and nuclear envelope breaks down. Spindle fibers grow from centrioles. Centrioles migrate to opposite poles of cell.

Process of protein synthesis

- DNA → mRNA → protein, with each arrow reading as "codes for the production of." - The step from DNA to mRNA is called transcription, and the step from mRNA to protein is called translation. - Transcription occurs in the nucleus, where the DNA is. - Most translation occurs in the cytoplasm, but 10% to 15% of proteins are synthesized in the nucleus, with both steps occurring there. - In the cisterna of the rough ER amino acids are removed and the protein is folded. - The protein leaves the ER in a transport vesicle and travels to the Golgi complex. - The protein is unloaded into the Golgi cisterna. - The Golgi complex modifies the protein by adding carbohydrate chains. - The finished protein is packaged inside Golgi vesicles that bud off the final Golgi cisterna. - Some Golgi vesicles become secretory vesicles which migrate to the plasma membrane and release the protein from the cell via exocytosis. - All three types of RNA are involved in protein synthesis.

G0 phase

- Describes cells that have left the cycle and cease dividing for a long time (or permanently). - Some cells leave the cell cycle for a "rest" and cease to divide for days, years, or the rest of one's life. The balance between cells that are actively cycling and those standing by in this phase is an important factor in determining the number of cells in the body. An inability to stop cycling and enter this phase is characteristic of cancer cells.

Cytokinesis

- Division of the cytoplasm during cell division.

Sister chromatids

- Each chromosome then consists of two parallel filaments of identical DNA. - The two identical copies of a single chromosome that are connected by a centromere.

Recessive allele

- Expressed only when present on both of the homologous chromosomes, that is, when the individual has no dominant allele at that locus. - Often codes for a nonfunctional variant of the protein.

mRNA

- It carries the genetic code from the nucleus to the cytoplasm. During its synthesis in the nucleus, it binds a protein cap that acts like a passport, permitting it to pass through a nuclear pore into the cytosol and tells a ribosome where to begin translation. - May contain uracil in it codon. - Binds to the small subunit of the ribosome. - Carries the genetic code to the ribosome. - It carries info from the nucleus to the cytoplasm. - It contains codons. - It carries a complementary copy of a gene.

G2 phase

- It finishes replicating its centrioles and synthesizes enzymes that control cell division. It also checks the fidelity of DNA replication and usually repairs any errors that are detected. - (Part of interphase) - A short period of time of growth and preparation for mitosis. during that time, the cell produces enzymes that control cell division, and also check and repairs the newly copied DNA.

Human Genome Project (HGP)

- It was carried out from 1990 to 2003, biologists now know the base sequence (A, T, C, G) of more than 99% of the genome. Findings: - Homo sapiens has far fewer genes than the 100,000 previously believed. - These genes generate millions of different proteins, so gone is the old idea of one gene for each protein. In its place is the realization that a single gene can code for many different proteins through alternative splicing of mRNA and other means. - Genes average about 3,000 bases long, but range up to 2.4 million bases. - All humans, worldwide, are at least 99.99% genetically identical, but even the 0.01% variation means that we can differ from one another in more than 3 million base pairs. Various combinations of these single-nucleotide polymorphisms account for all human genetic variation. - Some chromosomes are gene-rich (17, 19, 22) and some are gene-poor (4, 8, 13, 18, 21, and Y). - Before the HGP, we knew chromosomal locations of fewer than 100 disease-producing mutations; we now know more than 1,400, and this number will surely rise as the genome is further analyzed. This opens the door to a new branch of medical diagnosis and therapy called genomic medicine.

Termination

- Last/final step of translation when no free radicals are left to continue growth of the chain. - It occurs when a terminator codon arrives in the A site. - A stop codon is reached and the A site binds a release factor which caises the newly-synthesized polypeptide to be released from the ribosome. - When ribosome reaches stop codon a release factor binds to it. - Finished protein breaks away from ribosome. - Ribosome dissociates into two subunits.

Semiconservative replication

- Method of DNA replication in which parental strands separate, act as templates, and produce molecules of DNA with one parental DNA strand and one new DNA strand. - Each daughter DNA consists of one new strand (synthesized from free nucleotides) and one old strand (conserved from the parental DNA).

Cell cycle

- Most cells periodically divide into two daughter cells, so a cell has a life cycle extending from one division to the next. This cell cycle is divided into four main phases: G1,S,G2, and M. - Some cells like stomach cells divide rapidly. - Some cells leave the cell cycle for a "rest" and cease to divide for days, year, or the rest of one' life.

Anticodon

- On one loop of the tRNA molecule includes a series of three nucleotides complementary to a specific codon of mRNA. - A series of three nucleotides complementary to a specific codon of mRNA.

Aster

- Shorter microtubules from centrioles complete this, which anchors itself to inside of cell membrane. - Shorter microtubules form this, which anchors the assembly to the inside of the plasma membrane at each end of the cell.

Introns

- The "nonsense" portions of the pre-mRNA that must be removed before translation. - A pre-mRNA molecule that contains "nonsense" portions that must be removed before translation. Enzymes remove and degrade the ___ and splice the exons together into a functional mRNA molecule, which then leaves the nucleus. It may help you in remembering these if you think of ___ being removed while still in the nucleus and the exons being exported from the nucleus to undergo translation in the cytoplasm. - The "nonsense"; between exons that is removed BEFORE translation of messenger RNA and does not function in coding for protein synthesis.

Exons

- The "sense" portions of the pre-mRNA that will be exported from the nucleus and translated into protein. - A pre-mRNA molecule that contains "sense" portions that will be translated into a protein. Enzymes remove and degrade the introns and splice the ___ together into a functional mRNA molecule, which then leaves the nucleus. It may help you in remembering these if you think of introns being removed while still in the nucleus and the ___ being exported from the nucleus to undergo translation in the cytoplasm.

Initiation

- The 1st stage of translation; it involves a strand of mRNA associating with a ribosome, "locking" into place, and then having the amino acid Met is put in place during this stage. - Leader sequence in mRNA binds to small ribosomal subunit. - Initiator tRNA (bearing methionine) pairs with start codon. - Large ribosomal subunit joins the complex and the now fully formed ribosome begins reading bases.

Elongation

- The 2nd step of translation; ___ of the polypeptide; each new tRNA enters the ribosome at the A site and bonds with the codon of the mRNA. Amino acids attached to the tRNA at the P site are then transferred to the tRNA at the A site. The tRNA at the P site moves to the E site and leaves the ribosome. The tRNA at the A site, which now carries a chain of amino acids, moves to the P site. This process is repeated as the ribosome moves down the mRNA strand. - An amino acid is brought to the ribosome by tRNA and is joined to the nascent polypeptide chain. then the entire assembly moves one position along the mRNA. - Next tRNA (with its amino acid) binds to ribosome while its anticodon pairs with next codon of mRNA. - Peptide bond forms between methionine and second amino acid. - Ribosome slides to read next codon and releases initiator tRNA (empty). - Next tRNA with appropriate anticodon brings its amino acid to ribosome. - Another peptide bond forms (between 2nd and 3rd amino acids). - Process continually repeats, extending peptide to a protein.

Stop codon

- The 3 codons (UAG, UGA, and UAA) signal "end of message," like the period at the end of a sentence. - It enables the cell's protein-synthesizing machinery to sense that it has reached the end of the instruction for a particular protein. - The codon AUG plays 2 roles: It serves as a code for methionine and as a start codon. - The codon that signals to ribosomes to stop translation.

pre-mRNA

- The RNA produced by transcription and is an "immature" form. This molecule contains "sense" portions called exons that will be translated into a protein, and "nonsense" portions called introns that must be removed before translation. Enzymes remove and degrade the introns and splice the exons together into a functional mRNA molecule, which then leaves the nucleus. It may help you in remembering these if you think of introns being removed while still in the nucleus and the exons being exported from the nucleus to undergo translation in the cytoplasm.

Genomic medicine

- The application of our knowledge of the genome to the prediction, diagnosis, and treatment of disease. - It's relevant to disorders as diverse as cancer, Alzheimer disease, schizophrenia, obesity, and even a person's susceptibility to nonhereditary diseases such as AIDS and tuberculosis.

Cleavage furrow

- The area of the cell membrane that pinches in and eventually separates the dividing cell. - An indentation between the future cells that forms as cytokinesis progresses.

Contact inhibition

- The cessation of cell division in response to contact with other cells.

Telophase

- The chromatids cluster on each side of the cell. The rough ER produces a new nuclear envelope around each cluster, and the chromatids begin to uncoil and return to the thinly dispersed chromatin form. The mitotic spindle breaks up and vanishes. Each new nucleus forms nucleoli, indicating it has already begun making RNA and preparing for protein synthesis. - Chromosomes gather at each pole of cell. Chromatin decondenses. New nuclear envelope appears at each pole. New nucleoli appear in each nucleus. Mitotic spindle vanishes.

Metaphase

- The chromosomes are aligned on the on the cell equator, oscillating slightly and awaiting a signal that stimulates each of them to split in two at the centromere. The spindle fibers now form a lemon-shaped array called the mitotic spindle. Long microtubules reach out from each centriole to the chromosomes, and shorter microtubules form a star-like aster, which anchors the assembly to the inside of the plasma membrane at each end of the cell. - Chromosomes lie along midline of cell. Some spindle fibers attach to kinetochores. Fibers of aster attach to plasma membrane.

Comparison of DNA and RNA

- The most significant difference is that RNA is much smaller, ranging from 70 to 90 bases in tRNA to slightly over 10,000 bases in the largest mRNA. DNA by contrast, averages more than 100 million base pairs long. - Also, whereas DNA is a double helix, RNA consists of only one nucleotide chain, not held together by complementary base pairs except in certain short regions where the molecule folds back on itself. - The sugar in RNA is ribose instead of deoxyribose. - RNA contains three of the same nitrogenous bases as DNA (adenine, cytosine, guanine), but it has no thymine; a base called uracil (U) takes its place. - The essential function of the three principal RNAs is to interpret the code in DNA and use those instructions to synthesize proteins. RNA is a disposable molecule that works mainly in the cytoplasm, while DNA is irreplaceable and remains safely behind the nucleus, "giving orders" from there.

Mitotic phase

- The part of the cell cycle when mitosis divides the nucleus and cytokinesis divides the cytoplasm, producing two daughter cells. - A cell replicates its nucleus and then pinches in two to form two new daughter cells.

Penetrance

- The percentage of a population with a given phenotype that actually exhibits the predicted phenotype. - If 80% of people with the polydactyly allele actually exhibit extra digits, the allele has 80% of this.

Histones

- The proteins crucial for DNA packing. - They cluster in groups of eight molecules. - A DNA molecule winds around the cluster (like thread around spool). - Chromatin consists of thousands of repeating nucleosomes.

Transcription

- The step from DNA to mRNA; occurs in the nucleus, where the DNA is. - Process of copying genetic instructions from DNA to RNA (''transcribe a document"). - Copies genetic info from DNA to RNA. - Occurs in the nucleus. - Synthesis of codons and mRNA. - It requires the enzyme RNA polymerase. - Product of the reactions = mRNA

Double helix

- The structure of DNA, commonly described as this, and resembles a spiral staircase. - Each sidepiece is a backbone composed of phosphate groups alternating with the sugar deoxyribose. - The steplike connections between the backbones are pairs of nitrogenous bases. - The bases face the inside of the helix and hold the two backbones together with hydrogen bonds. - Across from a purine on one backbone, there is a pyrimidine on the other. - The pairing of each small, single-ringed pyrimidine with a large, double-ringed purine gives the DNA molecule its uniform 2 nm width.

Anaphase

- This phase begins with activation of an enzyme that cleaves the 2 sister chromatids from each other at the centromere. Each chromatid is now regarded as a separate, single-stranded daughter chromosome. One daughter chromosome migrates to each pole of the cell, with its centromere leading the way and the arms trailing behind. Migration is achieved by means of motor proteins in the kinetochore crawling along the spindle fiber as the fiber itself is "chewed up" and disassembled at the chromosomal end. Since sister chromatids are genetically identical, and since each daughter cell receives one chromatid from each chromosome, the daughter cells of mitosis are genetically identical. - Centromeres divide in two. Spindle fibers pull sister chromatids to opposite poles of cell. Each pole (future daughter cell) now has an identical set of genes.

Centrosome

- Two centrioles lie perpendicular to each other within a small clear area of cytoplasm. - Clear area near nucleus containing a pair of centrioles. - Organizing center for formation of microtubules of cytoskeleton and mitotic spindle.

Codominance

- Two different alleles both get expressed in the phenotype. - Two dominant alleles result in both phenotypes being expressed at the same time. - Example: Crossing a red bull with a white cow produces calves that are ROAN. Look at their fur closely, it is a blend of white hairs and red hairs, but no pink hairs! - Alleles that are equally dominant. When both of them are present, both are phenotypically expressed. - For example, a person who inherits allele IA from one parent and IB from the other has blood type AB. These alleles code for enzymes that produce the surface glycolipids of red blood cells. Type AB means that both A and B glycolipids are present, and type O means that neither of them is present.

Alternative splicing

- Variations in the way exons are spliced allow for a variety of proteins to be produced from one gene. - A mechanism in which one gene can code for more than one protein. Suppose a gene produced a pre-mRNA containing 6 exons separated by noncoding introns. These exons can be spliced together in various combinations to yield codes for 2 or more proteins. This is a partial explanation of how the body can produce millions of different proteins with no more than 25,000 genes.

Incomplete dominance

- When two different genes produce a phenotype that is a true blend of each of them. - A classic example is in the flower Mirabilis jalapa. Crossing a red flowered plant with a white flowered one produces PINK flowered offspring. - When two different alleles are present, the phenotype is intermediate between the traits that each allele would produce alone. - Individuals with two abnormal alleles die of heart attacks in childhood, those with only one abnormal allele typically die as young adults, and those with two normal alleles have normal life expectancies. Thus, the heterozygous individuals suffer an effect between the two extremes.

S phase

A cell makes a duplicate copy of its centrioles and all of its nuclear DNA. The two identical sets of DNA molecules are then available to be divided up between daughter cells at the next cell division. - (Part of interphase)

Stress proteins/heat shock proteins

A chaperone that is produced in response to heat or other stress on a cell and help damaged proteins fold back into their correct functional shapes.

Karyotype

A chart laying out the chromosomes in order by size and other physical features.

Punnett square

A chart that shows all the possible combinations of alleles that can result from a genetic cross.

Polyribosome

A cluster of several ribosomes reading one mRNA.

Prolactin

A hormone secreted by the anterior pituitary that targets the mammary glands stimulating them to produce breast milk.

DNA ligase

A linking enzyme essential for DNA replication.

Polygenic inheritance

A phenomenon in which genes at two or more loci, or even on different chromosomes, contribute to a single phenotypic trait. - Human eye and skin colors are an example of normal ___ traits. - They result from the combined expression of all the genes for each trait. Several diseases are also thought to stem from this, including some forms of alcoholism, mental illness, cancer, and heart disease.

ribosome tRNA

A ribosome has three pockets that serve as binding sites for tRNA: - In the course of translation, a tRNA usually binds first to the A site on one side of the ribosome, then shifts to the P site in the middle, and finally to the E site on the other side. - To remember the order of these sites, it may help you to think of A for the site that accepts a new amino acid; P for the site that carries the growing protein; and E for exit. (A and P actually stand for aminoacyl and peptidyl sites.) - A for the site that accepts a new amino acid; P for the site that carries the growing protein; and E for exit.

Transport vesicles

A small membranous sac in a eukaryotic cell's cytoplasm carrying molecules produced by the cell.

Unit of heredity

A trait passes from parent to offspring.

Mitotic spindle

An assemblage of microtubules and associated proteins that is involved in the movements of chromosomes during mitosis, and forms a lemon-shaped array.

Daughter chromosome

Anaphase begins with activation of an enzyme that cleaves the two sister chromatids from each other at the centromere. Each chromatid is now regarded as a separate, single-stranded, one of these. One ___ migrates to each pole of the cell, with its centromere leading the way and the arms trailing behind. - Migration is achieved by means of motor proteins in the kinetochore crawling along the spindle fiber as the fiber itself is "chewed up" and disassembled at the chromosomal end. - Since sister chromatids are genetically identical, and since each daughter cell receives one chromatid from each chromosome, the daughter cells of mitosis are genetically identical. - Sister chromatids that are separated by mitosis.

Diploid

Any cell with 23 pairs of chromosomes (somatic cells).

Posttranslational modification

As a protein is assembled on the ER surface, it threads itself through a pore in the ER membrane and into the cisterna. Enzymes in the cisterna modify the new protein in a variety of ways - removing some amino acid segments, folding the protein and stabilizing it with disulfide bridges, adding carbohydrates, and so forth. It occurs after protein synthesis; some proteins get modified.

Polydactyly

Caused by a dominant allele, it's the presence of extra fingers or toes.

Cells division

Cells divide when: - They have enough cytoplasm for two daughter cells. - They have replicated their DNA. - They have adequate supply of nutrients. - They are stimulated by growth factors (chemical signals). - Neighboring cells die, opening up space. Cells stop dividing when: - They snugly contact neighboring cells. - Nutrients or growth factors are withdrawn. - They undergo contact inhibition - the cessation of cell division in response to contact with other cells. - (1) they grow large enough to have enough cytoplasm to distribute to their two daughter cells; (2) they have replicated their DNA, so they can give each daughter cell a duplicate set of genes; (3) they receive an adequate supply of nutrients; (4) they are stimulated by growth factors, chemical signals secreted by blood platelets, kidney cells, and other sources; or (5) neighboring cells die, opening up space in a tissue to be occupied by new cells. - Cells stop dividing when they snugly contact neighboring cells or when nutrients or growth factors are withdrawn.

G1 phase

During this time a cell synthesizes proteins, grows, and carries out preordained tasks for the body, also accumulate the materials needed to replicate DNA in the next phase. - (Part of interphase)

DNA helicase

Enzyme that "unzips" DNA during replication by breaking the weak hydrogen bonds holding the nitrogen bases together, exposing its nitrogenous bases.

DNA polymerase

Enzyme that makes bonds between nucleotides, forming an identical strand of DNA during replication.

Gene regulation

Genes are turned on and off from day to day, even hour to hour, as their products are needed or not, and many genes are permanently turned off in any given cell.

Multiple alleles

Genes that exist in more than two allelic forms.

Regulatory protein (transcription activator)

It binds to regulatory sequences within an enhancer to stimulate or inhibit the rate of transcription initiation.

Nucleosomes

It consists of: - Core particle - A histone cluster with DNA (1.5 turns) around it. - Linker DNA - A short segment of DNA connecting core particles. - A structural unit of a eukaryotic chromosome, consisting of a length of DNA coiled around a core of histones. Each one consists of a core particle and a short segment of linker DNA leading to the next core particle. - Segments in a chromatin thread. - A DNA molecule wraps around a cluster of histones and appears as granules on the chromatin thread.

Law of complementary base pairing

It states that one strand governs the base sequence of the other. It enables us to predict the base sequence of one stand if we know the sequence of the complementary strand.

Interphase

That part of the cell cycle between one mitotic phase and the next, from the end of cytokinesis to the beginning of the next prophase. (G1, S, G2)

Sex chromosomes

The X and Y chromosomes which determines the sex of an individual.

Cytosine, Thymine

The bases in DNA that consists of a single carbon-nitrogen ring.

Adenine, Guanine

The bases in DNA that consists of double rings.

Spindle fibers

The centrioles begin to sprout elongated microtubules, which push the centrioles apart as they grow. Eventually, a pair of centrioles comes to lie at each pole of the cell. Some grow toward the chromosomes and become attached to the kinetochore on each side of the centromere. They then tug the chromosomes back and forth until they line up along the midline of the cell.

Gene pool

The combined genetic information of all the members of a particular population (the collective genetic makeup).

Genomics

The comprehensive study of the whole genome and how its genes and noncoding DNA interact to affect the structure and function of the whole organism.

Initiator tRNA

The first tRNA to bind to a ribosome at the start of translation. It always has the anticodon UAC and always carries the amino acid methionine.

Centromere

The point on a chromosome by which it is attached to a spindle fiber during cell division. It is where the sister chromatids come together at a pinched spot.

Replication fork

The point where the DNA is opened up, like the two halves of a zipper separating.

Meiosis

The production of eggs and sperm.

Kinetochore

The protein plaque on each side of the centromere. The protein structure on chromatids where the spindle fibers attach during cell division to pull sister chromatids apart.

Core particle

The spool of histones with the DNA ribbon around them.

Heredity

The transmission of genetic characteristics from parent to offspring.

Sex-linked traits

They are carried on the X or Y chromosome and therefore tend to be inherited by one sex more than the other.

Purines

Two of the bases in DNA (adenine (A) and guanine (G)) that consists of double rings.

Pyrimidines

Two of the bases in DNA (cytosine (C) and thymine (T)) that consists of a single carbon-nitrogen ring.

Clathrin

When rough ER is finished with protein: - It pinches off bubble-like transport vesicle coated with clathrin. - It helps select the proteins to be transported in vesicles and helps mold forming vesicle. - Vesicles detach from ER and carry protein to the nearest cisterna of Golgi complex. - A protein that apparently helps to select the proteins to be transported in the vesicles, and as a basketlike cage, it helps to mold the forming vesicles. Soon after the vesicles detach from the ER, they fuse into irregularly shaped clusters that carry their cargo to the nearest cisterna of the Golgi complex. Protein that plays a major role in vesicle formation during receptor mediated endocytosis; forms a coated pit on the plasma membrane.

Release factor

When the ribosome reaches a stop codon, its A site binds a protein called a ___ instead of a tRNA. The ___ causes the finished protein to break away from the ribosome and go off into the cytosol.

Chromosome territory

Where each chromosome is packed into its own spheroidal region. It is permeated with channels that allow regulatory chemicals to have access to the genes.