Exam 3- BIO-101

aneuploid

Having a chromosome number that is not an exact multiple of the haploid number.

sliding clamp

Holds DNA polymerase in place during strand extension (lagging strand synthesis)

sliding clamp

Holds DNA polymerase in place during strand extension (leading strand synthesis)

nondisjunction

If both homologs or both sister chromatids move to the same pole of the parent cell, the products of meiosis will be abnormal. The homologs fail to separate or disjoin. 1. Meiosis I starts normally. Tetrads line up in middle of cell. 2. Nondisjunction occurs with one set of homologs. 3. Meiosis II occurs normally. 4. Aneuploidy results, with all gametes having an abnormal number of chromosomes--too many or too few.

proofread

If the wrong base is added during DNA synthesis, the enzyme pauses, removes the mismatched base that was just added, and then proceeds with synthesis. For example, DNA polymerase III can do this, however it only reduces the error rate to one mistake per 10 million bases − Not accurate enough! If a mismatch such as the pairing of A with C occurs, DNA polymerase can act as a 5' to 3' exonuclease, meaning that it can remove bases in that direction.

epsilon subunit (∈)

In the case of E.coli cells with high mutation rates, biologists found that the mutation responsible for high mutation rates was a defect in a portion of the polymerase III enzyme.

genetic screen

Is any technique for picking certain types of mutants out of many thousands of randomly generated mutants.

somatic cells

Meaning cells that are not involved in gamete formation, and normally lack telomerase. As predicted, the chromosomes of these cells gradually shorten with each mitotic division, getting progressively smaller as an individual grows and ages.

single-strand DNA-binding proteins

Stabilizes single-stranded DNA (opening the helix)

RNA polymerase

Synthesizes RNA molecules according to the information provided by the sequence of bases in a particular stretch of DNA. Unlike DNA polymerase, RNA polymerase does not require a primer to begin connecting ribonucleotides together to produce a strand of RNA.

continuous strand (leading strand)

The enzyme's product is described as this because it leads into the replication fork and is synthesized continuously.

gene expression

The process of converting archived information into molecules that actually do things in the cell.

telomere

The region at the end of a linear chromosome.

Deoxyribose

-H group at 2' Carbon (DNA)

Ribose

-OH group at 2' Carbon (RNA)

synthesis of leading strand

1. DNA is opened, unwound, and primed. 2. Synthesis of leading strand begins.

nucleotide excision repair

1. Error detection. Enzymes detect an irregularity in DNA structure and cut the damaged strand. 2. Nucleotide excision. An enzyme excises a stretch of nucleotides that includes the damage. 3. Nucleotide replacement. DNA polymerase fills in the gap in the 5' to 3' direction. 4. Nucleotide linkage. DNA ligase links the new and old nucleotides.

metabolic pathways

A series of linked reactions in the cell; being with a particular reactant and terminate with a particular product. Also, each step may require a different enzyme.

knock-out

Alleles that do not function at all. By creating knock-out mutant alleles and analyzing their effects is still one of the most common research strategies in studies of gene function. Based on the analyses of knock-out mutants, the one-gene, one-enzyme hypothesis claimed that each gene contains the information needed to make an enzyme.

replisome

Although the enzymes are drawn at different locations around the replication fork, in reality most are joined into one large multi-enzyme machine. The lagging strand loops out as the leading strand is being synthesized.

5' to 3'

DNA polymerases can add deoxyribonucleotides to only the 3' end of a growing DNA chain. This is always the direction in which it proceeds. Builds 5' to 3', but reads 3' to 5'.

deoxyribonucleoside triphosphates (dNTPS)

DNA synthesis in cells involves polymerization reactions that are exergonic, because these are the monomers that act as the substrates in the reactions. Where N stands for any of the nitrogenous bases. Because the three phosphate groups are close together, there is high potential energy and it is enough to make phosphodiester bonds in a growing DNA strand exergonic.

Crick's proposition

Different combinations of bases could specify the 20 amino acids, just as different combinations of dots and dashes specify the 26 letters of the alphabet.

DNA polymerase III

Extends an Okazaki fragment (lagging strand synthesis)

DNA polymerase III

Extends the leading strand (leading strand synthesis)

eukaroytic linear chromosomal integrity

1. Telomeres do not contain genes that code for products needed in the cell. 2. An interesting enzyme called telomerase is involved in replicating telomeres.

one complete set of chromosomes

1. The chromosomes in each homologous pair must separate from each other during the first meiotic division, so that only one homolog ends up in each daughter cell. 2. Sister chromatids must separate from each other and move to opposite poles of the dividing cell during meiosis II.

monosomy

A condition in a diploid cell in which one chromosome of one pair is missing as a result of nondisjunction during meiosis.

topoisomerase

Breaks and rejoins the DNA double helix to relieve twisting forces caused by the opening of helix (opening the helix)

helicase

Catalyzes the breaking of hydrogen bonds between base pairs to open the double helix (opening the helix)

DNA ligase

Catalyzes the formation of a phosphodiester bond between the adjacent fragments.

DNA ligase

Catalyzes the joining of Okazaki fragments into a continuous strands (lagging strand synthesis)

primase

Catalyzes the synthesis of the RNA primer (leading strand synthesis)

primase

Catalyzes the synthesis of the RNA primer on an Okazaki fragment (lagging strand synthesis)

primer

Consists of a few nucleotides bonded to the template strand--because it provides a free 3' hydroxyl (-OH) group that can combine with an incoming dNTP to form a phosphodiester bond.

mismatch repair

Occurs when mismatched bases are corrected after DNA synthesis is complete.

discontinuous strand

Okazaki fragments are synthesized independently and joined together later, the lagging strand is also defined as this.

DNA polymerase

Polymerizes deoxyribonucleotides to DNA, which was found to catalyze DNA synthesis. There are several types of DNA polymerases.

Adenine (A)

Purine

Guanine (G)

Purine

Cytosine (C)

Pyrimidine

Thymine (T) (in DNA)

Pyrimidine

Uracil (U) (in RNA)

Pyrimidine

telomerase

Remarkable because it catalyzes the synthesis of DNA from an RNA template. In fact, the enzyme carries an RNA molecule with it that acts as a built-in template, allowing telomerase to add DNA onto the end of a chromosome and prevent it from getting shorter.

DNA polymerase I

Removes the RNA primer and replaces it with DNA (lagging strand synthesis)

messenger RNA (mRNA)

Short lived molecules of RNA carry information from DNA to the site of protein synthesis.

Okazaki fragments

These are short, newly synthesized DNA fragments that are formed on the lagging template strand during DNA replication. They are complementary to the lagging template strand, together forming short double-stranded DNA sections. They are between 1,000 to 2,000 nucleotides long in Escherichia coli and are between 100 to 200 nucleotides long in eukaryotes. They are separated by ~10-nucleotide RNA primers and are unligated until RNA primers are removed, followed by enzyme ligase connecting (ligating) the two Okazaki fragments into one continuous newly synthesized complementary strand.

replication bubbles

These grow as DNA replication proceeds, because synthesis is bidirectional, where it occurs in both directions simultaneously. The proteins responsible for recognizing the sites where replication begins and for the opening of the double helix. Such proteins are activated by the proteins that initiate the S phase in the cell cycle.