
Collagen

Melanin

Hemoglobin

Lactase
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Immunoglobulins
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Actin & Myosin
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They are ALL types of Proteins that do “work” that contribute to our genetic traits

DNA  RNA  Proteins
Honors Biology
Ms. 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


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


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)

1.
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 sequence
5.
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


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


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


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

1.
2.
mRNA binds to small rRNA subunit w/start codon,
AUG, in the “P” site 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


Mutation – any change in an organism’s genetic material

Causes

Mutagens – environmental agents that cause mutations after exposure
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X-rays, UV rays, chemicals
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Carcinogens – mutagens that lead to cancer

Asbestos, benzene, tobacco


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


Prokaryotic Cells – genes are unbroken set of nt

Operon
 controls gene expression in prokaryotes

Cluster of genes that code for proteins w/related functions


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


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