AP Biology Unit 6

pyrimidines

single-ringed nucleotides; uracil, cytosine, thymine

purines

double-ringed nucleotides; adenine, guanine

plasmids

small extra-chromosomal double-stranded circular DNA molecules; in the cytosol in prokaryotes, in the nucleus in eukaryotes

leading strand

strand of DNA that is continuously synthesized during replication

lagging strand

strand of DNA that is synthesized in fragments during replication

helicase

unwinds DNA strands

topoisomerase

relaxes replication fork supercoil

replication fork

where two strands of DNA are separated

DNA polymerase

requires RNA primers; attaches to the 3’ end and synthesizes new strands

ligase

joins lagging strand’s DNA fragments

transcription

process in which an enzyme directs the formation of an mRNA molecule

template strand

read by RNA polymerase in the 3’ to 5’ direction

messenger RNA

carries genetic information from DNA to ribosomes

codon

3-base sequence found on mRNA

transfer RNA

recruited to the ribosomes to help create a specific polypeptide sequence; directed by mRNA

anti-codon

3-base sequence on tRNA that, when matched to an mRNA codon, results in the release and addition of an amino acid to the growing polypeptide

ribosomal RNA

molecules that are functional units of ribosomes responsible for protein assembly

poly-A tail addition

enzyme-regulated modification that adds 100-200 adenine nucleotides to the mRNA transcript; aids in stability and nuclear export

GTP cap addition

enzyme-regulated modification that adds a modified guanine nucleotide; protects the transcript and helps the ribosome attach to mRNA

enzyme-regulated modifications

alterations to the mRNA transcript in eukaryotic cells

introns

non-coding sequences of an mRNA transcript

exons

coding sequences of an mRNA transcript

RNA processing

excision of introns and connection of exons to produce a mature mRNA transcript

alternative splicing

removes introns and connects retained exons; can produce different mRNA transcripts from one primary transcript

translation

process by which an mRNA sequence is used to generate a polypeptide; occurs on ribosomes

retrovirus translation

introduces viral RNA to host cells, which is then copied into DNA and integrated into the host genome, eventually assembling new viruses

reverse transcriptase

enzyme responsible for the conversion of viral RNA to viral DNA in retrovirus translation

initiation

rRNA interacts with mRNA at the first start codon; mRNA nucleotides are grouped into codons and read

start codon

AUG: methionine

stop codons

do not code for an amino acid; used to terminate translation

elongation

each tRNA brings an amino acid for rRNA to add to the growing polypeptide

termination

amino acids are added until a stop codon is reached; the newly-synthesized polypeptide is then released

mutations

changes in the genome of an organism; can be positive, negative, or neutral

gene mutations

changes in the nucleotide sequence of a particular gene; includes substitutions, insertions, and deletions

mutation causes

DNA replication or repair errors, radiation, or reactive chemicals

triploidy

3 copies of a chromosome; can result in sterility in some mammals

polyploidy

multiple sets of homologous chromosomes; can result in increased vigor in some plants

trisomy 21

47XX+21: when an individual has an extra chromosome

Turner syndrome

45XO: missing X chromosome

natural selection

process in which organisms better adapted to a particular environment have a higher chance of survival and reproduction, thereby passing those adaptations to the next generation

horizontal acquisition

exchange of genetic information between different genomes or unrelated organisms; primarily in prokaryotes

transformation

uptake of naked DNA from an external source

transduction

transmission of foreign DNA into a cell when a viral genome integrates with the host genome

conjugation

cell-to-cell DNA transfer via an external connection

transposition

movement of DNA molecules within and between DNA molecules

gene expression

process by which instructions in the DNA are transcribed and translated into a functional protein

regulatory sequences

stretches of DNA that can be used to promote or inhibit protein synthesis; interactions with regulatory proteins controls transcription

epigenetic changes

reversible modifications of DNA or histones

histones

proteins that DNA wraps around to condense into chromosomes

tissues

groups of cells that have the same function due to the presence of particular proteins in them

cell differentiation

cells within the same organism have the same genome but different phenotypes

transcription factors

proteins that promote/inhibit gene transcription

operons

groups of genes in prokaryotes that share an operator and promoter and are turned on/off together depending on if a repressor is bound to the operator

operator

sequence that either promotes or inhibits transcription by binding with regulatory proteins

inducers

molecules that can bind to the regulatory proteins and cause it to change shape (ex. allolactose)

promoters

DNA sequences upstream of the transcription start site where RNA polymerase and transcription factors bind to initiate transcription

gel electrophoresis

separates DNA fragments based on their size and charge

polymerase chain reaction (PCR)

allows scientists to create large samples of DNA when initial samples are small; DNA is denatured, primers are added, and DNA is replicated until ample DNA is obtained

bacteria transformation

bacterial cells take up foreign DNA from external sources; can be incorporated into the bacterial chromosome or exist in the cytosol as a plasmid; used to make medicines, modify food, or amplify DNA

DNA sequencing

determines the order of nucleotides; important in evolutionary biology, medicine, and forensics

parts of a nucelic acid

pentose, nitrogenous base, phosphate group

Okazaki fragments

discontinuously synthesized DNA fragments from the lagging strand during DNA replication

histone acetylation

adds acetyl groups to histones, neutralizing their positive charge, which increases gene expression

histone methylation

methyl groups are added to histone amino acids, which does not affect the histones themselves; can result in activation or repression of genes depending on context

DNA methylation

a methyl group is added to DNA, and usually represses gene transcription