Genetics

High School Biology Rapid Learning Series - 11

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Teach Yourself High School Biology in 24 Hours

Gene – Structures Ge e St uctu esand Functions

High School Biology Rapid Learning Series

Rapid Learning Centerwww.RapidLearningCenter.com/© Rapid Learning Inc. All rights reserved.

Wayne Huang, PhDAndrew Graham, PhDElizabeth James, PhD

Casandra Rauser, PhD Jessica Habashi, PhD

Sara Olson, PhDJessica Barnes, PhD



Learning Objectives

DNA: Chemical

By completing this tutorial, you will learn about:

Composition and Structure

Genes: the Genetic Code and the Central Dogma

How genes are inherited

Mutations and Genetic Disease

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Disease

Gene Therapy

Concept Map

Transcription

DNA Replication DNA

mRNA

tRNArRNA

Transcription

Transcription

Translation

Daughter cell

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Assembly

RibosomesProtein

TranslationAssembly

Amino acids

Assembly



DNA Structure

Chemical composition of DNA

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Physical structure of DNA

DNA organization in cells

Relationship between DNA and genes.

DNA and YouGenes dictate your phenotype.

Your weightYour face

6/52 Disease susceptibilityYour heightRate of aging



DNA Basics

DNA (deoxyribonucleic acid) is made up of genes.

Genes code for the physical development and

Genes are considered as the unit of genetic inheritance.

Cp y pphenotype of an organism. Chromosomes are

made up of genes and are associated with proteins. They are

located in the nucleus.

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The Building Blocks of DNAAdenine

Thymine

Nitrogenous Bases Guanine

Cytosine

BASE

Glycosidic Bond

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Nucleoside

Nucleotide monophosphate Deoxy-ribonucleic

AcidDeoxyribose+Phosphate Base +Nitrogenous

Base =

Deoxyribose



Chemical Composition

Four bases make up DNA: Adenine (A), guanine (G), cytosine (C) and thymine (T).A only pairs with T and G on pairs with C in DNA.

T GT CAT G C G TG TA C T

Backbone

DNA has a phosphate backbone.

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A C

T

A

GT

A

C

T

A

G

T

AC

G

T A

C G T

C G A C

G TA C

G

TBases

Backbone

Putting the DNA Blocks TogetherNitrogenous Bases

Phosphate

Deoxyribose

DNA Nucleotides are linked at their phosphate groups in a

3

5

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phosphate groups in a phosphodiester bond.

Notice the phosphate bonds are formed at the 5’ and 3’ positions.



Purine and Pyrimidine Nucleotides

(Adenine A)

(Guanine G)

Deoxyadenosine 5'-phosphate (dAMP) Deoxyguannine 5'-phosphate (dGMP)

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(Cytosine C) (Thymine T)

Deoxythymine 5'-phosphate (dTMP)Deoxycytosine 5'-phosphate (dCMP)

DNA Strands are AntiparallelThe arrangement of the components of DNA

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RNA DNA Structure Comparison

DNA RNABase: A, T, G, C A, U, G, CS D ib Rib

Major Differences between RNA and DNA:

Sugar: Deoxyribose Ribose3D Structure: Long, Double Helix Various Conformations

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Organization of DNA in the CellDNA is highly organized into chromosome within cells.

DNA strands

Double Helix

Nucleosome

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Chromosome(in cell nucleus)

Chromatin

Chromosome



Gene BasicsGenes are sections of the DNA

that code for a protein. There are many genes within a DNA or chromosome molecule.

This is chromosome 16. Notice the stripes which indicate genes.

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90 million base pairs are contained in this chromosome and dozens of genes.

Gene to Protein

Gene translation and transcription.Genetic code for protein sequence

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Genetic code for protein sequence.Central Gene DogmaProteins, amino acids and basic structure.



DNA to mRNA to ProteinDNA → mRNA → Protein

mRNA transcript is exported from the

nucleus to the cytoplasm

Newly formed peptide chain

Amino acid added to growing protein chain.

Amino acid

ribosome

tRNA

tRNA binding to codon

mRNA

Completed protein

Translation at the ribosome level

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Cytoplasm

Transcription TranslationmRNA

ribosomes

Start of polypeptide chain

Maturing protein

Different Types of RNA

tRNA carries amino acids to the ribosome and transfers

them to the growing polypeptide chain.

mRNA carries the information for the amino acid sequence

of a polypeptide (protein) chain. polypeptide chain.

rRNA are pieces of RNA that form complexes with

ribosomes (protein) to facilitate the transfer of

amino acid from tRNA to the polypeptide chain.

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snRNA forms complexes with proteins used in

eukaryotic RNA processing (e.g. exon splicing and

intron removal).

snoRNAs small nuclear RNAs used to process and chemically modify

rRNAs.



Types of RNA

mRNA encodes the amino acid sequence of

a polypeptide and is copied from DNA.

tRNA: transfer RNA, transports amino acids to the ribosomes

during translation.

copied from DNA.

rRNA: ribosomal RNA forms complexes with ribosomal proteins and is essential for the translation

of the mRNA sequence.

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snRNA: small nuclear RNA forms complexes with

proteins used in eukaryotic RNA processing, e.g. exon splicing, intron removal.

snoRNAs: small nucleolar RNAs guide chemical

modification of rRNAs and other RNA genes (tRNAs,

snRNAs). They are classed as snRNA.

Three Steps to RNA Synthesis

InitiationElongationTermination

Termination, elongation and initiation of RNA synthesis occurs in

Elongation is the same i k t d

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synthesis occurs in prokaryotes and

eukaryotes.

in prokaryotes and eukaryotes but initiation and

termination differ.



DNA is Transcribed to mRNA

DNA transcription begins with the unwinding and opening of

the DNA double helix.

Ultimately the mRNA is exported from the nucleus to the cytoplasm for translation

into a protein.

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A mRNA molecule complementary to the

DNA sequence is made.

Transcription

RNA copies information from DNA template through base-paring mechanism, UA/AT or CG/GC.

A GT CAT G C G TG TA C T

DNA Template(one strand)

U CAA UG ACU AC G A CG

Transcription Transcription

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RNA productU CAA UG ACU AC G A CG



RNA Synthesis ProcessRNA synthesis is regulated by gene

regulatory elements within each gene.

RNA polymerase unwinds the DNA and RNA is transcribed 5’ to 3’ from the

DNA template (3’ to 5’).

RNA synthesis is similar to DNA synthesis with these exceptions:

NTPs not dNTPs are used and there is no primer.

Uracil instead of thymine is used.

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And an RNA polymerase is used instead of a DNA

polymerase.

Processing of mRNAIn post transcriptional modification precursor

mRNA from eukaryotes are converted into mature mRNA (this is not post translational

The three main modifications are 5’capping, 3’

polyadenylation and RNA splicing.

modification).

1. 5’cap occurs while the RNA molecule is being transcribed after about 30 nucleotides have been added.

3. RNA splicing: introns (regions of RNA that do not code for protein) are removed from the pre-mRNA leaving exons connected. The splicing is catalyzed by a large protein complex called the spliceosome. There are many

24/522. Cleavage of the 3’ end is followed by adding polyadenosine (poly-A) tail.

ways to splice a mRNA allowing for a large variety of proteins from a limited amount of DNA.



Eukaryote transcription termination is not

completely defined but

Transcription TerminationProkaryotes and Eukaryotes have different

mechanisms to stop transcription.

Bacteria use two kinds of RNA t i ti t i ti t tcompletely defined but

seems to involve the cleavage of the nascent transcript, followed by template-independent

addition of A’s at the new 3’ end. This is called Poly-

adenylation.

transcription termination strategy: “Rho independent” type stops

transcription when the RNA molecule forms a hairpin loop structure followed by a whole

bunch of uracil bases.

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Protein Basics

There are 20 amino acid residues. The

amino acids are

The amino acid sequence of a protein is determined by the DNA sequence of the

gene.joined together by

a peptide bond.

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Typically one gene encodes for one protein. This is called the one gene one protein

hypothesis.



Introduction to Amino AcidsDo you know what an

amino acid is?Yes, an α amino acid has a central carbon atom, called an α carbon.

Amino acids also have an amino and carboxylic acid group.

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And an H and R group

Protein Basics

The sequence of amino acids is called the

primary structure of a

The protein sequence is determined by the DNA sequence of the gene.

Gene

protein.

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Protein (Gene Product)



The Central Dogma

DNA

How are genes converted into its final functional product?

DNA replication

Transcription

mRNA

Translation tRNA, rRNA, non-coding RNA

DNA replication

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Protein

The Genetic Code

DNA is made up of: Adenine, Guanine, Cytosine and Thymine.A codon is a three nucleotide sequence that codes for an amino acid.There are three codons that signal stop transcription.

Codons

Amin

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Amino

Acid



Protein Biosynthesis Three Phases

There are three phases in protein biosynthesis. Who

knows what they are?

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The Genetic CodemRNA is read in a sequential manner starting from a fixed point (initiation codon, AUG) and stopping at stop codons.

Every three bases on mRNA determine one amino acid (triplet code).

Each of 64 combinations (43) of triplet bases encodes an amino acid or a stop codon.

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One amino acid may be encoded by multiple codons .

The amino acid sequence is said to be degenerative because there are 64 codons for 20 amino acids.



Protein Biosynthesis - Elongation

Peptidyl tRNA attached to C-terminal of the growing

Incorporation of an Amino Acid Into a ProteinElongation:

Polypeptide chain

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DNA Replication

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3-Step Replication Process

Initiation

Elongation

Termination

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Transmission of Genes

A new cell derives its DNA from an older cell

Cell division and DNA Replication

from an older cell

An older cell prepares an extra set of DNA copies to give to its daughter cells (DNA replication)

The duplicated DNA is

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separated evenly into two daughter cells, with each cell containing one complete set of DNA



DNA Replication - DefinitionThe process of making an identical copy of a section of duplex (double-stranded) DNA, using existing DNA as a template for the synthesis of new DNA strands.

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Semi-Conservative DNA Replication

A parent DNA molecule is replicated

Original Parent Molecule

is replicated.

38/52First-generation daughter molecules

One parent strand is in each of the two new molecules.



DNA Replication ProcessThe parent double helix opens and a complementary

daughter strand synthesized.

Newly SynthesizedStrands

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The product of semi conservative replication is two double helices each having one new strand and one parent strand.

Initiation of ReplicationAt the origins of replication a replication fork emerges opening the double helix.

DNA strands separate at the origin and replication proceeds in

opposite directions along the DNA.

DNA replication is bidirectional.

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The strands are primed and replication proceeds from, the 5’ to 3’ direction.



Lagging Strand ReplicationIn DNA replication the lagging strand is the strand

opposite of the replication fork of the leading strands.

Replication is in the 3’ to 5’ direction.

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1. On the lagging strand primase reads the DNA and adds RNA sequences to act as a primer for POL III DNA polymerase. Multiple RNA primers needed.

2. Pol III lengthens the primers forming Okazaki fragments.3. Pol I then removes the RNA and adds its nucleotides.4. DNA ligase joins the fragments.

Leading Strand ReplicationThe leading strand is done in a single unit not fragments as it is in the lagging strand.

Replication is in the 5’ to 3’ direction.

Helicases are enzymes that move directionally along a

nucleic acid phosphodiester backbone separating two

annealed nucleic acid strands.

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1. On the leading strand Pol II reads the DNA and adds nucleotides continuously.

2. On the leading strand DNA polymerase III is able to synthesize DNA using free 3’OH group donated by a single RNA primer.

3. Continuous synthesis occurs in the direction the replication fork is moving.



Fidelity of DNA Replication

Mutations

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Genetic Diseases

Gene Therapy

DNA Mutations & HeredityA gene mutation is a permanent change in the DNA sequence that makes up a gene. Gene mutations occur in two ways:

they can be inherited from a parent

DNA Mutant Gene and Inheritance

they can be inherited from a parent acquired during a person’s lifetime.

Acquired (or somatic) mutations occur in the DNA of individual cells at some time during a person’s life due to environmental factors.Acquired mutations in somatic cells cannot be passed on to off spring.

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Mutations that are passed from parent to child are “hereditary mutations” or “germline” mutations.Mutations that are only in egg or sperm or those that happen immediately after fertilization are “de novo” mutations.



5 Basic Types of MutationsThese are the five basic DNA mutations.

Deletion Mutation Duplication Mutation Inversion

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Causes of Mutations

X

“X” Incorrect nucleotide inserted.

Errors during DNA replicationDNA damage caused by radiation, UV exposure or mutagenic chemicals.

X

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Chromosome translocation, deletion, duplication and inversion

There are many other causes of DNA mutations, including environmental and genetic instability.



Results of MutationsSilent mutations have a DNA base change but this change does not result in a different

amino acid in the protein.

Missense mutation is a DNA base change resulting in the insertion of a different amino

acid in the protein.p

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Nonsense mutations code for a stop where one

should not be. This results in a truncated protein.

Gene Therapy

First a piece of DNA having the normal or new gene is isolated.

Gene therapy may be used to fix a damaged gene or insert a new one.

The gene is inserted into a vector. A vector can carry the new gene to the target cell.

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Vector-DNA complex infects target tissue.

Replication of new gene begins and protein is synthesized.



Question: Review

Phosphate base + deoxyribose + nitrogenous base =

___________DNA

___________

___________

Adenine, guanine

Genes

Purine bases include ______ and _____.

Segments of DNA that code for a protein are called ____.

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___________Semi-conservativeDNA replication is _______.

Gene mutations happen in two ways. What are these ways?

___________Inherited or acquired

DNA → mRNA →Protein

DNA is transcribed to

DNA → mRNA →Protein

DNA is transcribed to

DNA BasesA:T adenine always pairs with thymine

DNA BasesA:T adenine always pairs with thymine

Learning Summary

5 Types of Mutations5 Types of Mutations

mRNA. mRNA is translated to

protein.

mRNA. mRNA is translated to

protein.G:C guanine pairs with cytosine.G:C guanine pairs with cytosine.

Result of DNA Result of DNA

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yp1. Deletion2. Duplication3. Inversion4. Insertion5. Translocation

yp1. Deletion2. Duplication3. Inversion4. Insertion5. Translocation

mutations include:1. Silent mutation.2. Missense.3. Nonsense.

mutations include:1. Silent mutation.2. Missense.3. Nonsense.



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Gene – Structures and Functions

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