BILD 1 Final COOPER UCSD

What is needed for a recessive X-linked trait to be expressed?

1) female needs 2 copies of the allele (homozygous)

2) male needs 1 copy of the allele (hemizygous) (thus more common in males)

silent mutations

different nucleotide in DNA but same amino acid in protein

Missence Mutation

when a point mutation results in substituting one amino acid for another

nonsense mutation

changes a normal codon into a stop codon

Law of Segregation

Mendel's law that states that the pairs of homologous chromosomes separate in meiosis so that only one chromosome from each pair is present in each gamete

law of independent assortment

Two or more genes assort independently—that is, each pair of alleles segregates independently of any other pair during gamete formation. (only applies to genes on different chromosomes)

Incomplete Dominance

Phenotype of heterozygous is intermediate between the homozygous dominant and recessive (blended)

Codominance

Phenotype is affected by two different alleles in separate and distinguishable ways

Nondisjunction (and result)

Error in meiosis in which homologous chromosomes fail to separate.

Result: 1 gamete receives 2 of the same type of chromosome and the other receives no copy

Epistasis

A type of gene interaction in which one gene alters the phenotypic effects of another gene that is independently inherited.

Helicase

Enzymes that untwist the double helix at the replication forks

Single strand binding proteins

hold DNA strands apart

Semi conservative replication

Each half of an original DNA molecule serves as a template for a new strand, and the two new DNA molecules each have one old and one new strand.

Topoisomerase

A protein that functions in DNA replication, helping to relieve strain in the double helix ahead of the replication fork by twisting and rejoining DNA strands

What aspects of genomes and cell structure makes DNA replication more complicated in eukaryotes than prokaryotes?

- circular vs. linear DNA

- prokaryotes don't have a nucleus

- prokaryotes have 1 chromosome; humans have 46

RNA primer

short segment of RNA used to initiate synthesis of a new strand of DNA during replication

DNA polymerase require a primer to which they can add nucleotides

Primase

makes a short RNA molecule (~10 base pairs) that creates a small double stranded section

Hershey-Chase Experiment

determined that DNA is the genetic material

DNA polymerase

An enzyme that catalyzes the synthesis of new DNA at replication fork

DNA ligase

Joins DNA together to make one continuous strand

Okazaki fragments

Small fragments of DNA produced on the lagging strand during DNA replication, joined later by DNA ligase to form a complete strand.

DNA polymerase I

replaces RNA primer with DNA

DNA polymerase III

makes new DNA strand by adding nucleotides one at a time to the 3' end

Histones

Responsible for the first level of DNA packing in chromatin

gene

A DNA sequence that is expressed to form a functional product: either RNA or polypeptide

Leading strand

The new continuous complementary DNA strand synthesized along the template strand in the mandatory 5' to 3' direction.

Lagging strand

A discontinuously synthesized DNA strand that elongates by means of Okazaki fragments (joined together by DNA ligase), each synthesized in a 5' to 3' direction away from the replication fork.

Gene expression

The process by which DNA directs protein synthesis, includes two stages: transcription and translation

Transcription +product

Synthesis of RNA using information in DNA

Produces mRNA

Translation +site

Synthesis of a polypeptide using the information in the mRNA

Ribosomes are the site (ribosomes found on rough ER and in the cytoplasm)

https://www.youtube.com/watch?v=jnP8_1eIfgo

What separates transcription and translation in eukaryotic cells?

The nuclear envelope

Primary transcript

The initial RNA transcript from any gene prior to processing

Central dogma

Concept that cells are governed by a cellular chain of command:

DNA → RNA → Protein

Template strand

Provides a template for ordering the sequence of complementary nucleotides in an RNA transcript

will be 3' to 5'

Codon

mRNA base triplets that provides genetic code information for a particular amino acid (position on polypeptide)

How many condons are there?

64

61 for amino acids and 3 are stop signals to end translation

What are the 3 stages of transcription?

1) Initiation

2) Elongation

3) Termination

Transcription factors

Mediate the binding of RNA polymerase and the initiation of transcription

Promoter

Region of DNA just before the part that will be made into the mRNA

situates RNA polymerase

TATA box

A promoter crucial in forming the initiation complex in eukaryotes

Pre-mRNA processing

(only in eukaryotes)

1. 5' cap & Poly-A tail

2. Splicing

5' cap & Poly-A tail

Prevent mRNA from being broken down in the cytoplasm

Splicing

removal of introns (RNA sequences that do not get translated into proteins)

Termination of transcription, prokaryotic vs eukaryotic

Prokaryotic: polymerase stops transcription at the end of the terminator and the mRNA can be translated without further modification

Eukaryotic: RNA polymerase II transcribes the polyadenylation signal sequence; the RNA transcript is released, 10-35 nucleotides past this polyadenylation sequence

Introns

Noncoding segments of DNA that lie in between coding regions

Can have sequences that regulate gene expression

Exons

Eventually expressed, usually translated into amino acid sequences

What are the 3 properties RNA that enable it to function as an enzyme?

It can form a three-dimensional structure because of its ability to base-pair with itself

Some bases in RNA contain functional groups that may participate in catalysis

RNA may hydrogen-bond with other nucleic acid molecules

Do prokaryotes have introns? +why

No, because they have transcription coupled to translation. They don't have time/space for that, since intron splicing will stop the coupling

Do eukaryotes have introns? + why

Yes, they evolved the nucleus, where splicing can be done

Transfer RNA (tRNA)

helps decode a mRNA sequence into a protein

Initiation

- Small subunit of RNA is holding a tRNA; slides down the RNA until it finds the "AUG"

- Large subunit comes (uses GTP)

Elongation

Chain broken of P-site tRNA, goes to A-site tRNA, everything slides down one, once in E-site gets kicked out

Termination

- Ribosome reaches stop codon

- Release factor

3 Binding sites for tRNA

EPA

eating

pink

apples

P site

Holds the tRNA carrying the growing polypeptide chain

A site

Holds the tRNA that carries the next amino acid to be added to the chain

E site

Discharged tRNAs leave the ribosome E for exit

What signals the start of translation?

The start codon AUG

Operon

a unit made up of linked genes which is thought to regulate other genes responsible for protein synthesis

Repressible operon

transcription is usually on, but can be inhibited (repressed) when a specific small molecule binds allosterically to a regulatory protein (example tryptophan)

Inducible operon

usually off, but can be stimulated (induced) when a specific small molecule interacts with a regulatory protein (example lac operon)

corepressor

a small molecule that cooperates with a repressor protein to switch an operon off

inducer

A specific small molecule that inactivates the repressor in an operon (turns operon on)

Regulatory gene

a gene that produces a repressor substance that inhibits an operator gene

DNA Methylation

The addition of methyl groups to bases of DNA after DNA synthesis; may serve as a long-term control of gene expression.

Chromatin structure

More dense DNA is not used as frequently

Epigenetics

the study of environmental influences on gene expression that occur without a DNA change

Transgenerational Exposure

Generations out: effects of exposure on gene expression/epigenetic markers

transcription factors

Bind to promoter; situate RNA polymerase

Enhancers and Activators

(similar to transcription factors) Small bits of DNA (further away in DNA); stabilize RNA polymerase

Alternative splicing

Post-translational RNA modification process in which some exons are removed

Mutually-exclusive exons get cut out

3 + 4 = mutually exclusive

1235

1245

x inactivation

one of two X chromosomes is randomly inactivated and remains coiled as a Barr body