Exam 5

Define homozygous

if an individual has two of the same alleles for a gene

define heterozygous

if an individual has two different alleles for a gene

define gene

the basic unit of heredity

define allele

alternative versions of a gene that may produce a distinct protein

define homologous pair

a set of two matching chromosomes, one from mom one from dad

define locus

the area of the chromosome the gene resides

define phenotype

what you physically look like, defined by genotype

define genotype

the combination of alleles an individual has

define punnett square

a grid used to predict probability of traits in offspring

define complete dominance

one allele is fully dominant over the other

define codominance

two alleles are both expressed in heterozygotes

define incomplete dominance

neither allele is completely dominant, phenotype will be half of each

define sex-linked dominance

occurs when the dominant gene causing a trait is located on the x chromosome

what does diploid mean

has two complete sets of chromosomes

what does haploid mean

single set of unpaired chromosomes

what do genes code for

the sequence of amino acids in assembling proteins

what is an individuals genotype

the combination of alleles an individual has

How does an individual’s genotype correlate with their phenotype?

genotype is the instruction manual, expressed in phenotype

how many pairs of chromosomes do humans have and where do they come from

23 pairs, half from mothers egg, half from fathers sperm

where are genes found in the cell

on chromosomes, almost always in the nucleus

what is polygenic inheritance

a trait controlled my more than one gene

explain epistasis

where the presence of one gene affects the phenotypic expression of another gene

what did Erwin Chargaff do

he discovered the amount of adenine=thymine and the amount of cytosine=guanine

what are chargaffs rules

always a 1 to 1 ratio of pyrimidine to purine

what are mendel’s laws

law of dominance, law of segregation, law of independent assortment

what were the findings of rosalind franklin

she used x-ray photographs to DNA fibers, revealing helical structure and nucleotides

what are purines

double ringed structures adenine and guanine

what are pyrimidines

single ringed structures thymine, cytosine, and uracil

what molecules comprise a nucleotide

pentose sugar, phosphate group, nitrogenous base

Distinguish between the 3' and 5' ends of DNA

3’ has a hydroxyl group attached to third carbon of terminal sugar, 5’ has phosphate group attached to fifth carbon of terminal sugar

how do nucleotides form to make nucleic acids

dehydration synthesis, covalent bond between phosphate group on 5’ end of one sugar and hydroxyl group on 3’ end of another sugar

what does antiparallel mean

parallel, but moving in opposite directions, one strand runs 5-3 complementary runs 3-5

define phosphodiester linkage

covalent bond that holds together the sugar-phosphate backbone of DNA and RNA

define semiconservative replication

new DNA molecule contains one template strand and one newly synthesized strand

define replication fork

Y shaped area where double helix is unzipping

define bidirectional synthesis

when two replication forks form at an origin and work in opposite directions outward

define leading strand

strand synthesized continuously in the 5’ to 3’ direction

define lagging strand

strand synthesized in short segments (Okazaki fragments)

define okazaki fragments

newly synthesized DNA fragments formed on the lagging strand

define telomeres

sequences of DNA at the end of chromosomes that do not contain genes, shorten with each cell division

define proofreading

an incorrect base pairing stalls DNA polymerase 3

define nucleotide excision repair

mechanism that removes faulty dna segment, and dna polymerase 3 repairs the gap

discuss the roles of helicase

separates the genes, pulls double strands apart

discuss the roles of single strand binding protein

prevents single strands from going back together

discuss the roles of topoisomerase

cuts DNA to relieve tension caused by unwinding

discuss the roles of DNA polymerase 3

main enzyme in replication, a new stand is created in the 5’ to 3’ direction

discuss the roles of RNA primase

creates short sequence of RNA at the origin of replication

discuss the roles of exonuclease

corrects errors in dna replication be removing incorrect nucleotides

discuss the roles of DNA polymerase 1

removes RNA primers, replaces with new DNA

discuss the roles of DNA ligase

forms covalent bonds between DNA fragments to make new continuous DNA strand

define transcription

segment of DNA is transcribed into RNA

define dna template

a single strand of dna used to synthesize a new complementary strand

define RNA polymerase

catalyzes dehydration reaction, unwinds dna double helix, assembles rna nucleotides

define transcription factors

initiates or inhibits RNA polymerase

define promoter region

section of DNA that serves as binding spot for RNA Polymerase

define TATA box

the specific dna sequence (promoter) that is the binding spot for general transcription factors

define initiation complex in transcription

a lot of proteins, including rna polymerase and transcription factors, that bind to a promoter to initiate transcription

define elongation in transcription

RNA polymerase adds RNA nucleotides from 5’ to 3’

define termination in transcription

RNA polymerase detaches from DNA and RNA strands

define pre-mRNA

immature/incomplete RNA strand

define mRNA

messenger RNA, the only type translated into a protein

define snRNA

small nuclear RNA, involved in RNA processing

define tRNA

transfer RNA, brings the amino acid to the ribosome

what are the four bases used in RNA (full names)

Adenine, Uracil, Guanine, Cytosine

define termination region in transcription

the 3’ end of a gene that signals RNA polymerase to stop transcribing

what is a polyadenylation signal

the signal to disconnect new RNA strand from DNA and add a string of Adenine (Poly-A Tail)

where does transcription take place

in the nucleus

define 5’ cap

GTP molecule added to 5’ end

define introns

noncoding regions of RNA that are removed

define exons

regions of RNA that code for protein (being expressed)

define spliceosome

a complex of proteins plus snRNAs that cuts out introns, joining exons to be continuous

define alternative splicing

creation of multiple different functional proteins by keeping/cutting various exons

what are three functions of RNA modifications

to protect from degradation, regulate export out of the nucleus, assist with ribosome attachment for translation

what does UTR stand for

untranslated region (not used for proteins)

where are UTRs located on pre-RNA

before the start codon, after the stop codon

what are spliceosomes made of

proteins and snRNA

where does RNA processing take place

the nucleus

define codons

3 adjacent RNA nucleotides

define start codon

first sequence that translates into a protein (AUG)

define stop codon

signals cell to end translation, they do not code for amino acids

define redundant code

more than one sequence codes for the same amino acid

define ambiguous code

sequences never code for more than one amino acid

define silent mutation

if the mutation doesnt change the amino acid

define nonsense mutation

changes DNA sequence into premature stop codon

define missense mutation

changes the amino acid

define frame-shift mutation

the addition/subtraction of a nucleotide causing all amino acids downstream to change

define anticodon

three nucleotides found on tRNA that are complementary with a sequence on mRNA

define A Site

“waiting room” where the next aminoacyl tRNA is lined up

define P Site

where new amino acid is growing a polypeptide

define E Site

where tRNA exits the ribosome

what is on either side of tRNA

anticodon on one side, amino acid on the other side

what enzyme adds the amino acid to tRNA

aminoacyl-tRNA synthetase

what is the structure of a ribosome, what is it made of

one small subunit, one large subunit, composed of proteins and rRNA

what is a tRNA molecule with an amino acid attached called

aminoacyl-tRNA

Where does the first tRNA attach during translation

the P Site

what is a polysome

mRNA/ribosome complex attached to more than one ribosome

where does translation take place

in the cytoplasm on ribosomes

define mutation

changes in DNA sequence

define point mutation

single nucleotide changes

define substitution mutation

one nucleotide is replaced by another