Collagen Melanin Hemoglobin Lactase Immunoglobulins Actin & Myosin

They are ALL types of Proteins that do “work” that contribute to our genetic traits

What do all of these have in common?

Protein Synthesis

DNA RNA Proteins

Honors BiologyMs. Pagodin

Summarize the structure and function of genes

Describe the function of ribosomes

Differentiate between DNA and genes

Describe the structure and function of DNA

State the base pairing rules

Review…

Compare RNA & DNA

RNA (Ribonucleic Acid) Single Strand of Nucleotides 5 C sugar is ribose Uses the N base uracil (U) instead of

thymine (T) 3 Types:

Messenger RNA (mRNA) An RNA copy of the gene Carries and delivers genetic info from nucleus to

ribosome Ribosomal RNA (rRNA)

Components of a ribosome Site of translation

Transfer RNA (tRNA) Acts as an interpreter Translates mRNA into amino acid sequences

All 3 types of RNA are essential for processing information from DNA to proteins.. Gene Expression or Protein Synthesis

Gene Expression Organisms traits are determined

by proteins Proteins are assembled according

to genes on DNA DNA can not leave the nucleus,

but proteins are made in ribosomes, therefore need an intermediate messenger… RNA

2 stages: Transcription – copying DNA

info to mRNA (nucleus) Translation – mRNA used to

build protein (cytoplasm)

Overview

Transcription1. RNA polymerase binds to promoter region of DNA

Promoter region – specific sequence of DNA that serves as a START signal

2. DNA unwinds and 2 strands separate only 1 side is used as a template

3. RNA polymerase reads each nucleotide on the 3’ end and pairs it with a complimentary RNA nucleotide

Same base pairing rules except “U” pairs with “A” RNA dangles off the enzyme like a tail

4. Proceeds at 60 nt/sec until RNA polymerase reaches a specific STOP sequence5. RNA is released as a free transcript

Introns are cut out before mRNA leaves the nucleus

mRNA is a copy of exons (coding) and introns (non-coding) regions

Alternative splicing - Introns allow for evolutionary

flexibility, genes to shuffle, and limits effects of mutations

Add a 5’ cap Binds to ribosome

Add a 3’ Poly-A tail 100-300 adenine

ribonucleotides Determines how long mRNA

will last in the cytoplasm

mRNA Processing

Only part of the DNA strand is unwound and used as a template

The enzyme RNA polymerase adds ribonucleotides

Results in a single RNA strand

Compare Transcription to DNA Replication

The Genetic Code Instructions for building a protein

are written as codons on mRNA Codons – 3 nt that code for a

specific a.a. Codon chart - a.a. and stop

signals that are coded by each of 64 possible sequences of mRNA codons

Highly Conserved (Universal) – the genetic code is the same in ALL organisms…significance?

Ex. GUC codes for the a.a. valine in bacteria, dogs, lizards, humans, etc

Reading the codon chart

tRNA – one loop has 3 nt sequence called an anticodon Anticodon – 3nt complimentary to codon on mRNA Enables tRNA to temporarily H-bond to mRNA No tRNA w/anticodons for STOP codons UAG, UAA,

UGA tRNA also carries the a.a. that corresponds to CODON

Ribosomes 1,00’s in cytoplasm 2 rRNA subunits (large and small) bind together to

form ribosome 3 Binding Sites

A site – where tRNA anticodon binds to complimentary codon of mRNA

P site – holds tRNA w/ growing polypeptide chain E site – tRNA exits, leaving a.a. in the “P” site

Translation

Initiator tRNA w/ anticodon UAC binds to small ribosomal subunit

mRNA start codon binds to tRNA anticodon and finally a large ribosomal subunit binds to the initiation complex

Translation: Initiation

Translation: Elongation

Translation: Termination

Translation: Assembling the Protein

1. mRNA binds to small rRNA subunit w/start codon, AUG, in the “P” site

2. tRNA w/ anticodon UAC and carrying a.a. methionine binds to start codon

3. The next codon, in “A” site, binds w/ complimentary tRNA (carrying the corresponding a.a.)

4. Enzyme forms a peptide bond between adjacent a.a.

5. tRNA in “P” site now exits via “E” site and is recycled

6. tRNA in the “A” site moves to the “P” site w/ growing polypeptide chain, mRNA moves w/it, therefore a new codon is in the “A" site

7. Process continues until it reaches a STOP codon at the end of the mRNA, there is no anticodon

8. W/nothing in the “A” site, the ribosome is disassembled and the newly made polypeptide is released

Protein Synthesis

Mutation – any change in an organism’s genetic material

Causes Mutagens – environmental agents that cause

mutations after exposure X-rays, UV rays, chemicals

Carcinogens – mutagens that lead to cancer Asbestos, benzene, tobacco

Mutations

Chromosomal Mutations Alterations in chromosome structure Deletion, duplication, inversion, translocation

Point Mutations Just one or a few nt changed in a gene Substitution – one nt is replaced by a different nt

Ex. UGU UGC (no effect b/c both code for cysteine) UGU UGA (early STOP codon)

Frameshift mutations Mutations that cause a gene to be read in the wrong 3 nt sequence Insertions – one or m ore nt added to gene

Ex. AAU CGC UUU AGA UCG CUU U

Deletions – one or more nt deleted from gene Ex. AAU CGC UUU AUC GCU UU

Note * If mutation occurs in an intron it will have no effect*if reading frame is displaced 3 nt, the mutation may have no effect

Types of Mutations

Prokaryotic Cells – genes are unbroken set of nt

Operon controls gene expression in prokaryotes Cluster of genes that code for proteins

w/related functions

Prokaryotic Gene Regulation

Lac Operon Lac Operon – genes for lactose

digesting enzyme Only want lactose digesting

enzymes when lactose is present…or else energy is being wasted transcribing genes

Operator – acts like an on/off switch If no molecule is bound to operator,

then the gene is “ON” and RNA polymerase can move across

When a repressor protein binds to the operator, it blocks the RNA polymerase from transcribing, genes are “OFF”

Repressor can be removed by inducer (ex. allolactose), now gene is turned ‘ON”

Trp Operon – genes for making tryptophan

E.coli would typically get trp from environment, therefore gene only needs to be turned on when trp is not present

Trp Operon

No operons…b/c genes w/similar functions are scattered among different chromosomes

Multicellular organisms have different types of cells, all somatic cells contain the same DNA…but what makes them different is which genes are turned on/off Ex. Every cell has hemoglobin genes, but only turned

“ON” in rbc Transcription takes place at uncoiled regions of

chromosome RNA polymerase cannot bind w/o transcription factors Transcription factors are signaled by 20 messengers

that bind to the enhancer site to turn “ON” the gene

Eukaryotic Gene Regulation