Proteins & Genes: BIO 107

Let 36 - 42

in prokaryotes, genes are inside

chromosomes and plasmids

in eukaryotes, genes are inside

nucleus, chromosomes, and mitochondria

which strand can be a template strand for a gene

either strand

strand: 5’ to 3’

3’ to 5’

mRNA genes are usually

single copy

tRNA & rRNA genes are usually

multiple copies

Why do so many of your mRNA genes have introns?

serve crucial roles in increasing protein diversity

Where are RNA Pols found inside the nucleus?

nucleolus

Where are rRNA genes found?

nucleolus

Where are mRNA and tRNA found?

euchromatin

Where is the centromere storage DNA?

heterochromatin

Protein synthesis Is also called

translation

it requires ___ nucleotides to form 1 amino acid

3

Protein synthesis is done by

ribosomes

initiation mechanism

1. ribosomes bind to mRNA at start codon

elongation mechanism

1. tRNAs deliver the amino acids

2. amino acids are linked by peptide bonds

tRNA structure

has anticodon that matches with mRNA codon

termination mechanism

1. process ends when it reaches stop codon

2. protein is released

ribosome structure

1 large subunit

1 small subunit

3 tRNA binding site

1 mRNA binding site

tRNA binding site

EPA

E

tRNA exits

P

tRNA is held

A

tRNA enters

which is moving so that the codons can be read?

the ribosome

the mRNA strand

Are there tRNA’s for stop codons? Why?

No, release factors recognize this and terminate

Yes, tRNA’s recognize this and terminate

primary structure

linear sequence of amino acids determined by codons in the mRNA

secondary structure

a- helix or b-sheets

tertiary structure

determined by primary // interactions with R-group

quarternary structure

multiple polypeptide chains joined together

Eukaryotic mRNAs have

single protein coding region

Prokaryotic mRNAs have

several protein coding regions

operon definition

A DNA region responsible for making an mRNA with more than one protein-coding region

advantage of having operons

allow prokaryotes to adapt to changing environments

do eukaryotes have operons?

no

do prokaryotes have operons?

yes

which proteins have localization signals?

plasma membrane, cell wall, or export

which proteins do not have localization signals?

cytoplasmic

How do proteins get delivered in Euk. cells to cytosol?

receives no signals

How do proteins get delivered in Euk. cells to nucleus?

Signal = "Put me in an organelle"

How do proteins get delivered in Euk. cells to export?

Signal = "Make me at the ER"

How do proteins get delivered in Euk. cells to plasma membrane?

Signal = "Put me in a membrane"

NLS definition

acts as a signal to direct the protein to the nucleus

which proteins have NLS?

DNA Pols, RNA Pols, & Histones

which organelles have their own ribosomes?

mitochondria and chloroplast

gene regulation: unicellular organisms

Only make proteins needed for the environment

gene regulation: multicellular organisms

Only make proteins needed for the cell type

General transcription factors

Bind to many genes and recruit RNA Pols

Positive transcription factors

Bind to one or more specific genes & recruit RNA Pols

• increase gene activity
  

Negative transcription factors

Bind to one or more specific genes & blocks the promotor

• decrease gene activity
  

Mutation definition

are random changes in DNA sequence

Base-pair substition

Replacement of one bp with another

Indel

Insertion or deletion of one or more bp

Mutations in the promoter

harder for RNA pol to bind

does a mutation in the promoter increase or decrease RNA synthesis

decrease

increase

Mutations in the protein coding region #1

bp substitution → silent mutation

silent mutation

won’t affect type of protein formed

Mutations in the protein coding region #2

bp substitution → missense mutation

missense mutation

wrong amino acid; may be non-functional

Mutations in the protein coding region #3

bp substitution → nonsense mutation

nonsense mutation

stop codon inserted; non-functional

Mutations in the protein coding region #4

idel → frameshift mutation

frameshift mutation

shifts amino acids; typically non-functional