NEW AP Biology Unit 6 Gene

nucleotide

the basic unit of nucleic acids composed of a sugar, phosphate group, and nitrogenous base

nucleic acids

polymers of nucleotides; DNA and RNA

purines

nitrogenous bases with two rings (adenine and guanine)

pyrimidines

nitrogenous bases with one ring (cytosine, thymine, uracil)

prokaryotic DNA

double stranded, circular, smaller, one chromosome, in cytosol

eukaryotic DNA

double stranded, linear, larger, multiple chromosomes, in nucleoi & mitochondria & chloroplast

plasmid

small circular extra-chromosomal DNA molecule found in prokaryotes (and some eukaryotes) that replicates independently

Chargaff’s rule

DNA base pairing rule stating A pairs with T and C pairs with G; total % of purines = total % of pyrimidines

antiparallel

opposite orientation of DNA strands (5’→3’ and 3’→5’)

phosphodiester bond

covalent bond between nucleotides in a DNA strand

hydrogen bond

weak bond holding complementary DNA bases together

semiconservative replication

DNA replication model where each daughter molecule contains one old strand and one new strand

origin of replication

specific DNA sequence where replication begins

replication fork

y-shaped region where DNA is actively being replicated

helicase

enzyme that unwinds DNA by breaking hydrogen bonds

topoisomerase

enzyme that relieves DNA supercoiling ahead of the replication fork

single-strand binding proteins

SSBPs; proteins that keep separated dna strands from rejoining

primase

enzyme that synthesizes RNA primers for dna replication

RNA primer

short RNA segment that provides a starting point for DNA polymerase

DNA polymerase III

enzyme that adds DNA nucleotides in the 5’→3’ direction

leading strand

DNA strand synthesized continuously toward the replication fork

lagging strand

DNA strand synthesized discontinuously away from the replication fork

Okazaki fragments

short DNA fragments formed on the lagging strand

DNA polymerase I

enzyme that replaces RNA primers with DNA nucleotides

DNA ligase

enzyme that joins Okazaki fragments together

telomere

repetitive dna sequence that protects chromosome ends

telomerase

enzyme that extends telomeres in eukaryotic cells

mRNA

RNA molecule that carries genetic information from DNA to ribosomes

tRNA

RNA molecule that brings amino acids to the ribosome

rRNA

RNA molecule that forms the core of ribosomes

codon

three-nucleotide sequence on mRNA that codes for an amino acid

redundancy of the genetic code

multiple codons coding for the same amino acid

transcription

process of synthesizing RNA from a DNA template

promoter

dna sequence where RNA polymerase binds

TATA box

eukaryotic promoter sequence rich in T and A bases

RNA polymerase

enzyme that synthesizes RNA and attaches to the promoter

transcription factors

help RNA polymerase bind; detach from TIC after initation

transcription initiation complex

TIC; includes transcription factors, regulatory proteins and genes, and RNA polymerase

polyadenylation signal

AAUAAA; signals the end of transcription in pre-mRNA

RNA processing

modification of pre-mRNA into mature mRNA

5’ cap

modified guanine added to the 5’ end of mRNA for protection

poly-A tail

string of adenines (50-250) added to the 3’ end of mRNA

intron

non-coding region removed from RNA

exon

coding region that remains in mature mRNA

alternative splicing

different combinations of exons producing multiple proteins

translation

process of synthesizing a polypeptide from mRNA

ribosome

cellular structure that carries out protein synthesis

A site

ribosomal site where incoming tRNA binds

P site

ribosomal site holding the growing polypeptide

E site

ribosomal site where trna exits

start codon

AUG codon that initiates translation

stop codon

codon that signals termination of translation

chaperone protein

protein that assists in folding polypeptides

reverse transcriptase

couples viral RNA to DNA in the host cell

operon

cluster of genes regulated together in prokaryotes

operon structure

promoter, operator, genes, regulatory genes

repressible operon

operon usually on but turned off by a repressor

inducible operon

operon usually off but activated by an inducer

lac operon

inducible operon involved in lactose metabolism

trp operon

repressible operon involved in tryptophan synthesis

epigenetics

heritable changes in gene expression without dna sequence changes

histone acetylation

modification that loosens chromatin and increases transcription

DNA methylation

modification that condenses chromatin and reduces transcription

differential gene expression

different genes expressed in different cell types

cell differentiation

process by which cells become specialized; involves transcription factors

apoptosis in cell specialization

allows structures to take form, e.g. preventing webbed fingers

mutation

change in the genetic material of an organism; main source of genetic variability

large scale mutation

nondisjunction, translocation, inversions, duplication, deletion

nondisjunction

when chromosomes do not separate properly in meiosis

small scale

point mutations, frameshift mutations

point mutation

change in a single nucleotide, e.g. substitution

frameshift mutation

mutation that alters the reading frame; nucleotide insertion or deletion

silent mutation

mutation that does not change amino acid sequence

missense mutation

mutation that changes one amino acid

nonsense mutation

mutation that introduces a stop codon

impact of mutation

depends on the environmental context

aneuploidy

unusual number of chromosomes

mutations in agriculture

triploid bananas, polyploid strawberries; increase size, vigor, and sterility

horizontal gene transfers

exchange of genetic information between different genomes of unrelated organisms; mostly prokaryotes

transformation

uptaking of DNA from nearby cell (external environmental source)

transduction

when a viral genome integrates with the host genome

conjugation

cell-to-cell transfer of DNA through contact

transposition

movement of DNA segments within and between DNA molecules, e.g. crossing over, elements copied from bacterial chromosome to plasmids

gel electrophoresis

technique that separates DNA fragments by size

polymerase chain reaction

PCR; technique used to amplify DNA sequences

DNA sequencing

determining the order of nucleotides in DNA using a lazer