BIOL110: EXAM #4 (CH. 14,15,16,17)

father of genetics

Gregor Mendel

mendel’s interest

inheritance…”heritable factor”

mendel’s technique

1) remove stamens

2) sperm-bearing pollen to egg-bearing carpel

3) pollinated carpel matures

4) plant seeds from pod

5) examine offspring

mendelian genetics

study of inheritance

gene

sequence of DNA with instructions to build proteins or RNAs (20,000 genes in humans)

locus

physical location of a gene on chromosome

allele

an alternative version of a gene

dominant allele

determines appearance; fully expressed

shown in CAPITAL LETTERS

recessive allele

no effect when paired with dominant

2 recessive allele —> trait observed

shown in lowercase letters

phenotype

observable characteristic (ex: flower color)

genotype

genetic make-up (ex: combination of P alleles)

homozygous dominant

PP

heterozygous

Pp

homozygous recessive

pp

F1 generation

P generation offspring (Pp)

P generation

true-breeding parents (PP x pp)

F2 generation

F1 self-pollination offspring (PP, Pp, or pp)

punnett square

used to predict offspring

mendel’s first law: law of segregation

two alleles of a gene separate during meiosis and end up in different gametes

experiments following 1 character (monohybrid cross)

one allele for each gamete

mendel’s second law: law of independent assortment

two or more genes assort independently during meiosis; each pair of alleles segregates independently of other allele pairs

the assortment is happening independently —> no buddy system

experiments following 2 characters (dihybrid cross)

minimum number of genes for assortment is 2

incomplete dominance

neither allele completely dominant - intermediate phenotype (ex: snapdragons)

codominance

two alleles affect phenotype in separate, distinguishable ways

alleles equally visible

blood type A

genotype: I^AI^A or I^Ai

blood type B

genotype: I^BI^B or I^Bi

blood type AB

genotype: I^AI^B

blood type O

genotype: ii

autosomal recessive inheritance

albinism, cystic fibrosis, sickle-cell disease

autosomal dominant inheritance

achondroplasia, Huntington’s disease

sex-linked inheritance

on the sex chromosome (X and Y)

focuses on x-linked recessive inheritance

ex: red-green colorblindness, Duchenne muscular dystrophy, hemophilia

DNA

the molecule of heredity; connected by phosphodiester bonds

DNA sequence

order of bases

genome

genetic material of organism or virus

coding or non-coding information

chemical polarity of DNA

5’ end (phosphate end), 3’ end (hydroxyl end)

structure of DNA

nitrogenous base, sugar, and phosphate group

base pairing

A-T and C-G

A-T has 2 hydrogen bonds

C-G has 3 hydrogen bonds

first step of DNA replication

as DNA replication begins, the hydrogen bonds connecting the two strands are broken, causing the strands to separate

second step of DNA replication

each “old” strand of DNA serves as a template for the construction of a “new complementary strand

third step of DNA replication

when DNA replication is completed, there are two DNA molecules, each with one old strand and one new strand

DNA polymerase

adds complementary nts to 3’ end of pre-existing chain

primase

adds nts to a primer

helicase

untwists/unwinds double helix at replication fork separating strands

template

single-strand binding proteins prevent re-pairing

origin of replication

short, specific DNA sequences recognized by proteins —> replication bubble

semi-conservative model

half of the strand is new, half of the strand is old

central dogma

flow of genetic information; how we get from a gene to a protein

gene expression

information encoded in DNA direct synthesis of proteins or RNAs

differences between DNA and RNA

DNA is double-stranded, RNA is single-stranded

deoxyribose vs ribose

thymine is substituted for uracil

transcription

making an RNA copy of DNA

transcription initiation

a eukaryotic promotor attaches to the TATA box…several transcription factors bind to DNA…transcription initiation complex forms

transcription factor

proteins that recognize the TATA box and bind to it

transcription elongation

reading in a 3’ to 5’

synthesizes in a 5’ to 3’

follows base pairing of RNA

transcription termination

polyadenylation signal sequence transcribed

RNA transcript cut free from polymerase 10-35 nts later

RNA processing

ends of pre-mRNA modified

5’ cap

guanine + phosphate added to end

3’ end

poly-A tail

RNA splicing

introns removed; exons spliced together

enzymes recognize very specific sites in the introns that cut on each end

mRNA

carries genetic message via codons

codon

basic unit of genetic code; nucleotide triplet

64 codons total

stop codons

tells the mRNA to stop coding

UAA, UAG, UGA

start codon

tells the mRNA to start coding

AUG

genetic code

redundant, no ambiguity, nearly universal

redundant

multiple codons code for multiple amino acid

no ambiguity

every codon has one meaning

nearly universal

almost every living organism uses exactly this code

tRNA

transfer amino acid from cytoplasmic pool to growing chain in ribosomes; carries amino acids

anticodon

nt triplet - base pairs to mRNA codons (still contains U)

ribosomes

site of protein synthesis

E site

used tRNA exits (no longer contains amino acid)

P site

formation of the peptide bonds

A site

where tRNA are accepted into the ribosome (carrying an amino acid)

translation initiation

1) H-bonds form: sets reading frame

2) small subunit of ribosome, with initiator tRNA bound to it, binds 5’ cap and scans for AUG (start codon)

3) large subunit binds forming translation initiation complex…GTP hydrolysis provides energy for assembly

translation elognation

three step cycle: codon recognition, peptide bond formation, translocation

codon recognition

anticodon of incoming tRNA binds with mRNA codon in A site

peptide bond formation

amino acids connected by peptide bond-catalyzed rRNA of large subunit

translocation

ribosome moves: A site becomes empty—> P site growing chain —> E site used tRNA exits & reuploaded

translation termination

1) ribosome reaches a stop codon on mRNA, A site accepts release factor

2) release factor promotes hydrolysis, freeing polypeptide

3) ribosomal subunits and other components dissociate

mutation

change in DNA, spontaneous, mutagens

mutagens

chemicals that cause mutations

point mutation

change in single nucleotide pair of gene

wild type

normal gene sequence

nucleotide-pair substitution: silent

do not have an observable effect on the organism’s phenotype

nucleotide-pair substitution: missense

DNA change that results in different amino acids encoded at a particular position in the resulting protein

nucleotide-pair substitution: nonsense

a change in DNA that causes a protein to terminate or end its translation earlier than expected

insertion/deletion

adding or deleting nucleotide pairs

nucleotide-pair insertion

frameshift causing immediate nonsense; inserted an extra nucleotide

nucleotide-pair deletion

frameshift causing extensive missense; causes a change in amino acid sequence

3 nucleotide-pair deletion

no frameshift, but amino acid missing; completely changes the polypeptide chain