BIOL 1406 Lecture Exam 4

Pedigrees

track inheritance in a family over several generations

Sperm donor

Square on pedigree chart represents who?

Egg donor

Circle on pedigree chart represents who?

Affected

Filled shapes on pedigree chart are individuals that show trait or disorder

Dominant traits

The following are examples of?

• Widow’s peak

• Free earlobes

• Straight thumb

• Wet earwax

• PTC taster

Recessive traits

The following are examples of?

• No widow’s peak

• Attached earlobes

• Hitchhiker’s thumb

• Dry earwax

• PTC non-taster

Dominant

_______ disorders are rarer

Heterozygous genotype = affected

Recessive

_________ disorders are more common

Heterozygous genotype = carrier

Inbreeding

_______ leads to higher probability of mating carriers of a recessive disorder

ABO blood types

determined by the two alleles a person has of the blood group gene

the three possible alleles are I^A, I^B, and i

Codominant

I^A and I^B alleles are _______ (both dominant).

Polygenic inheritance

an additive effect of two or more genes on a single phenotypic character

ex: eye, skin, hair color

Multifactorial characters

many factors, both genetic and environmental, collectively influence phenotype

X-linked recessive disorders

The following are examples of what in humans?

• Color blindness

• Duchenne muscular dystrophy

• Hemophilia

• Baldness

Female chromosome

XX

Male chromosome

XY

Sex-linked gene

a gene located on either sex chromosome

Aneuploidy

genetic condition due to incorrect number of chromosomes

can be caused by nondisjunction in meiosis

Disjunction

proper separation of chromosomes during cell division

Nondisjunction

the improper separation of chromosomes during cell division

Deletion

occurs when a chromosomal fragment is lost

too small

Duplication

occurs when chromosomal segment repeats a segment

too large

Inversion

occurs when a chromosomal fragment reattaches to original in reverse

section flipped and unusable

Translocation

occurs when a chromosomal fragment leaves original and joins a nonhomologous chromosome

Extensions of mendelian genetics

• Different types of dominance are possible

• A gene can have more than two possible alleles

• Polygenic inheritance

• Multifactorial characters

• Sex-linked genes

Prokaryotic cell

• Lacks nucleus

• Has less DNA

• DNA arranged as single chromosome (usually circular)

Eukaryotic cell

• Has membrane-bound nucleus

• Has much more DNA

• Linear DNA arranged as several different chromosomes

• Has organelle DNA

Deoxyribonucleic acid

DNA stands for…

5’ end

the “head” end of DNA strand

3’ end

the “tail” end of DNA strand

Nucleotide

________ strands are antiparallel and complementary

Phosphodiester bonds

hold together nucleotides in a strand

Hydrogen bonds

hold the two nucleotide strands together

Adenine : thymine

What DNA base pair is this?

A : T

Cytosine : guanine

What DNA base pair is this?

C : G

Adenine : uracil

What RNA base pair is this?

A : U

Semiconservative model

In DNA replication, each nucleotide strand is template for a new nucleotide strand

away

DNA replication proceeds in both directions _______ from an origin.

Origins of replication

short stretches of DNA that have a specific sequence of nucleotides marking where replication of DNA begins

Replication fork

a Y-shaped region where the parental strands of DNA are being unwound

at each end of replication bubble

Helicases

enzymes that untwist the double helix at the replication forks, separating the two parental strands and making them available as template strands

Single-strand binding proteins

bind to the unpaired DNA strands, keeping them from re-pairing

Topoisomerase

an enzyme that breaks, swivels, and rejoins the parental DNA ahead of the replication fork, relieving the strain caused by unwinding

Primase

synthesizes short complementary RNA primers for DNA polymerase III in E.coli

DNA polymerase rules

• Needs starting point (primers)

• Reads template strand from 3’ end to 5’ end

• Makes new complementary DNA strand from 5’ end to 3’ end

continuously

3’ to 5’ template strand is read and replicated ________.

discontinuously

5’ to 3’ template strand is read and replicated ________.

Leading strand

new DNA nucleotide strand that is made continuously

template is 3’ to 5’ in overall direction of DNA strand replication

Lagging strand

new DNA nucleotide strand that is made discontinuously (as Okazaki fragments)

template is 5’ to 3’ in overall direction of DNA strand separation

DNA polymerase III

starts as primer, reading template strand and linking nucleotides to synthesize new DNA

DNA polymerase I

replaces RNA primers with correct DNA nucleotides

DNA ligase

seals “nicks” in DNA backbone after DNA polymerase I does its job

DNA replication step 1

Helicase unzips hydrogen bonds holding nucleotides together

DNA replication step 2

Single-strand binding proteins stick to single nucleotide strands to keep them separated from each other

DNA replication step 3

Primase makes 2 RNA primers and places them in correct regions to mark where to begin replication process

DNA replication step 4

DNA polymerase III binds to primers and builds in direction of primer, making single-strand complementary DNA

DNA replication step 5

DNA polymerase I removes RNA primers and makes single strand DNA to fill gaps

DNA replication step 6

DNA ligase uses dehydration reaction to connect DNA polymerase I pieces with new covalent bonds

Gene expression

the process by which DNA directs the synthesis of proteins

occurs whenever the RNA or protein is needed

RNA polymerase rules

• Doesn’t require primers

• Only ONE DNA nucleotide is read

• Makes single-stranded RNA that is antiparallel and complementary to DNA strand

Transcription steps

1. Initiation

2. Elongation

3. Terminaiton

Transcription

the synthesis (production) of RNA using information in the DNA

P transcription initiation

RNA polymerase binds to the correct promoter sequence in DNA

DNA strands are locally unwound

E transcription initiation

Transcription factors bind to the correct promoter sequence in DNA and recruit RNA polymerase to promoter

DNA strands are locally unwound

Promoter

DNA sequence where RNA polymerase attaches and initiates transcription

Terminator

DNA sequence that signals the end of transcription

Transcription elongation

RNA polymerase transcribes part of ONLY ONE DNA strand from its 3’ end to 5’ end

Makes single stranded RNA that is antiparallel and complementary to transcribed DNA strand

DNA strands reanneal as elongation proceeds

same in prokaryotes and eukaryotes

P transcription termination

Terminator sequence in the DNA is transcribed

RNA polymerase detaches from DNA and releases RNA

E transcription termination

Polyadenylation signal in the DNA is transcribed

Special proteins release RNA from RNA polymerase

RNA processing

in eukaryotes, pre-mRNA is modified to create finished mRNA by adding guanine cap to 5’ end and poly-A tail to 3’ end

protein coding region is spliced

RNA splicing

large portions of the RNA primary transcript molecules are removed (introns) and the remaining portions are reconnected (exons)

Exons

sections that will be translated to make protein primary structure

“Coding” segments

Introns

sections that will be removed during RNA processing

“Noncoding” segments

Spliceosome

large complex made of proteins that removes introns and joins exons in correct order during pre-mRNA splicing

Alternative splicing

removal and rearrangement of both introns and exons resulting in two or more different polypeptides in RNA processing

Ribosomes

molecular complexes that facilitate the orderly linking of amino acids into polypeptide chains

Ribosome structure

made of two protein subunits and rRNA

Ribosome purpose

• matches each mRNA codon to complementary tRNA

• tRNA delivers amino acids to it one at a time

• joins amino acids by forming peptide bonds

Transfer RNA

delivers individual amino acids to ribosome

tRNA

Each _______ has an anticodon that is complementary to a mRNA codon.

Translation

the synthesis of a polypeptide using the information in the mRNA

Translation initiation

at “start” codon = ^5’AUG^3’

• ribosome subunits assemble

• tRNA methionine binds to start codon

Translation elongation

• ribosome moves up the mRNA one codon at a time

• tRNA brings ribosome amino acids to add to protein

Translation termination

at “stop codon”

• release factor plugs up A-site of ribosome

• ribosome subunits detach

• releases protein in primary structure

Operons

special prokaryotic DNA that help prokaryotes respond to environmental changes

Operon genes

_______ are transcribed as one mRNA but translated to make more than one protein

Inducible operon

gene expression is normally OFF and must be turned ON

ex: lactose operon

Repressible operon

Gene expression is normally on and must be turned off

Silent mutation

this mutation has no observable effect on the phenotype

Missense mutation

this mutation substitutes one amino acid for another one, and has little effect on the protein

Nonsense mutation

this mutation causes translation to be terminated prematurely; resulting polypeptide is shorter than normal

Frameshift mutation

this mutation occurs whenever the number of nucleotides inserted or deleted is not a multiple of three

Repressor

binds to the operator, preventing RNA polymerase from transcribing the genes

Inducer

small molecule that inactivates the repressor

Lactose absent

_________, repressor active, operon OFF

Lactose present

________, repressor inactive, operon ON

Lac operon

contains 3 genes that encode enzymes that control E. coli lactose uptake and breakdown

Transcription step 1

activator proteins bind to distal control elements groups as an enhancer in the DNA

Transcription step 2

a DNA-bending protein brings the bound activators closer to the promoter

Transcription step 3

the activators bind to certain mediator proteins and general transcription factors, helping them form an active transcription initiation complex on the promoter