dna, cell cycles and genetics! mrs. stahl biology

DNA, Cell Cycles and Genetics!

Mrs. StahlBiology

Let’s Think!!!!

• What does DNA stand for?• Where is DNA located in the cell?• What is DNA to you?• Where do we find DNA?

1928- Fredrick Griffith’s Experiment• Looked into the bacterium that

causes pneumonia. • One form is coated by

carbohydrates and is smooth (S form) while the other form is rough.

• He injected the mice and the smooth ones died, when the S bacteria was killed with heat first, the mice lived.

• Combo- R and heat treated S= mice died. Found S bacteria in the blood. Some of the S bacteria must have transferred into the R. The R became harmful.

• Conclusion: Transforming Principle

Why did this happen?

• Heating bacteria to 60 C (140 F) can kill the bacteria without denaturing (falling apart) their DNA. DNA can remain unchanged up to 90 C (194 F). Therefore, the S bacteria in Griffith’s experiment died, but their DNA remained intact.

Oswald Avery- 1944

• Figured out what the transforming principle was by observing it in a Petri dish.

• Conducted three tests:– 1. Qualitative- chemical tests showed that there weren’t any

proteins, but DNA was present.– 2. Chemical Analysis- Elements in the extract (sample) closely

matched those found in DNA.– 3. Enzyme Tests- tested the reaction to certain enzymes. Added

to the extract enzymes that breakdown proteins, the extract still transformed the R bacteria to the S form. Transformation did not occur when they added an enzyme to destroy the DNA .

– Conclusion- DNA is the transforming principle.

Hershey and Chase 1952• Studied bacteriophages-> a type of

virus that takes over a bacterium’s genetic machinery and directs it to make more viruses.

• They are ones responsible for confirming that DNA is the genetic material.

• They used radioactive sulfur (found in proteins ) and radioactive phosphorus (found in DNA)

Hershey / Chase Experiment

• Experiment 1:– Infected bacteria with

bacteriophages grown in radioactive sulfur; separated bacteria from the phages, found no activity in the bacteria.

• Experiment 2:– Infected bacteria with

bacteriophage grown in radioactive phosphorus; separated bacteria from bacteriophages; found significant radioactivity inside the bacteria, which showed that DNA from the bacteriophage had entered the bacteria.

Final Result

• DNA is the genetic material.

Watson and Crick determined the three-dimensional structure of DNA by building models.

• They realized that DNA is a double helix that is made up of a sugar-phosphate backbone on the outside with bases on the inside.

The Structure of DNA• Deoxyribonucleic Acid• Very long polymer or chain of repeating units• Monomers are called nucleotides

– Each nucleotide is made up of a sugar, phosphate, and nitrogenous base (ATGC)

– A= Adenine– T= Thymine– C= Cytosine– G= Guanine

Structure Continues• Double helix / twisted ladder• Backbone= sugars and

phosphates• Strands are complementary -

they fit together and are opposite each other.

• Base pairs are held together by hydrogen bonds.

• Sugars and phosphates are held together by covalent bonds.

• http://www.youtube.com/watch?v=p835L4HWH68

Why would the middle / nitrogenous bases be held

together by hydrogen bonds and the “backbone” or sides be made

up of covalent bonds?

Answer

• Base pairs are held together by weak, hydrogen bonds because the strands need to be able to break apart so that they can replicate. The sides of the latter need to be strong to keep the strand in tact when it splits a part to replicate.

Label the DNA Molecule

T

A

C

G

A T

C G

Hydrogen Bonds Phosphates

Sugars

Covalent Bonds

Chargaff’s Rule

• Base pairs match up– A always binds with T (held

together by 2 hydrogen bonds)– C always binds with G (held

together by 3 hydrogen bonds)• The bonds that hold them

together are hydrogen bonds • Example- ACACAC, what is the

complementary strand?

CG

TA

hydrogen bond covalent bond

Sugars

Phosphates

Let’s Practice- Find the Complementary Strand

• 1. TGCATTGC• 2. ATATAGCTAG• 3. ATA• 4. CAT• 5. TATGC

How do Forensic Scientists determine if someone commits a crime? What do they look at?

• Fingerprints• Blood• Saliva• Cheek Cells• Straws, cigarettes• Hair sample

Do they all have the same DNA?If so how?

Why do you always have to cut your hair, fingernails, and the lawn?

• Growth caused by new cells being made.

Cells divide at different rates.

• The rate of cell division varies with the need for those types of cells.

• Some cells are unlikely to divide (G0).

Cells divide at different rates- cont.

• Prokaryotic cells divide faster than eukaryotic cells.

• Go= cells that rarely divide but still function– Ex- neurons and muscle cells– Ex- lymphocytes= part of your immune system ->

B cells and T cells. They don’t divide until they recognize an invader and then they rapidly divide to fight that antigen.

Cell Size

• Cells are limited in size by their surface area to volume ratio– Cells can get so large that they can no

longer obtain enough oxygen and nutrients at which point they divide.

• Surface area must allow for adequate exchange of materials.– Cell growth is coordinated with division.– Cells that must be large have unique

shapes.

Cell cycle• A regular pattern of growth, DNA replication, and

cell division that occurs in eukaryotic cells.• 5 main stages:

– 1. Gap 1– 2. Synthesis– 3. Gap 2– 4. Mitosis– 5. Cytokinesis

Interphase

Gap 1 or G1 Synthesis or S Phase Gap 2 or G2

• Cell growth •Cells increase in size and organelles increase in number• Critical checkpoint to make sure that the DNA is perfect and that there are no imperfections.

• Copies the DNA- DNA Replication, Transcription and Translation occur here.• By the end the cells nucleus contains two complete sets of DNA.

• Additional growth• Critical checkpoint to make sure that the DNA is not damaged and that the cell is adequate size.

First Stop- Interphase

Let’s Look at Synthesis a little closer

• DNA Replication, Transcription, and Translation

DNA Replication

• The process by which DNA is copied during the cell cycle and occurs in the nucleus.

• A single DNA strand can serve as a template or pattern for a new strand.

• Assures that every cell has a complete set of identical genetic information.

• Your DNA is divided into 46 chromosomes that are replicated during the S phase of the cell cycle. Your DNA is copied once in each round of the cell cycle = complete set of DNA for each cell.

DNA Replication Continues

• The enzyme helicase unzips the double helix in both directions to separate the strands of DNA. Breaking the hydrogen bonds holding them together.

• Nucleotides are free floating in the nucleus and can pair up with the nucleotides from the existing DNA strands.

• DNA polymerase (enzyme) bonds the new nucleotides together, creating a new strand.

The DNA molecule unzips in both directions.

DNA polymerase

new strand nucleotide

Step 1

Step 2

original strand new strand

Two molecules of DNA

Stage 3

DNA Transcription• Now that we have

replicated or duplicated our DNA we now need to transcribe it. The ultimate goal is to make proteins so now we need to break the DNA down into RNA- Ribonucleic Acid.

replication

transcription

translation

Transcription Continues

• Defined as : The process of making RNA from DNA and occurs in the nucleus.

• RNA= Ribonucleic Acid• The nitrogenous bases change a bit. Instead of T or

Thymine, RNA has U or Uracil.• A-U and C-G are paired up together.• Example of a DNA Strand: TACGGAC• Example of an RNA Strand: AUGCCUG• Do the examples in your notes!

Facts about RNA

• Sugar is ribose• It’s single stranded and not double stranded.

This allows them to catalyze reactions much like enzymes do. Speed things up.

• It has Uracil instead of Thymine.

Transcription Cont….

• Only a gene is transferred not a chromosome.• Catalyzed by RNA polymerase (enzyme)• Created three types of RNA

• Messenger RNA (mRNA) carries the message that will be translated to form a protein.

• Ribosomal RNA (rRNA) forms part of ribosomes where proteins are made.

• Transfer RNA (tRNA) brings amino acids from the cytoplasm to a ribosome.

Next Step- Translation• Now lets take the RNA and turn it into a protein /

amino acid.• Occurs in the cytoplasm and uses mRNA• We have 20 amino acids. Now we will string together

nucleotides to make amino acids that the body can use.

• The sequences are called codons and they are made up of three letters each. Each codon codes for an amino acid.

• AUG = start codon-> start of translation• UAA, UAG, and UGA= stop codons-> signal the end of

amino acid chain.

codon formethionine (Met)

codon forleucine (Leu)

The genetic code matches each RNA codon with its amino acid or function.

mRNA Recap

• Short lived• Carries instructions from DNA in the nucleus

to the cytoplasm• Read in a set of three nucleotides or codons

• HOW DOES IT TRANSLATE A CODON INTO AN AMINO ACID????

Ribosomes and tRNA molecules!!

Ribosomes consist of two subunits.

– The large subunit has three binding sites for tRNA. Holds the growing protein.

– The small subunit binds to mRNA.

tRNA• Adaptor – just like a plug in an outlet. One

end is the amino acid and the other is the anticodon (a set of three nucleotides that are complementary to a mRNA codon.

• Example- Codon= GGG, the anticodon would be CCC

End Result

• New proteins for the cells to use.• The whole process is continual

Videos

• www.cellsalive.com/mitosis.htm• http://www.youtube.com/watch?v=C6hn3sA0i

p0&feature=related• http://www.youtube.com/watch?v=lf9rcqifx34• http://www.youtube.com/watch?v=efyV-YxV0

P0&feature=related

Next Stop- Mitosis & Cytokinesis

• Mitosis is defined as the division of the cells nucleus and its contents.

• Cytokinesis is the division of the cytoplasm• Results in 2 identical daughter cells.• In this process the nuclear membrane dissolves

and the duplicated DNA condenses around proteins and separates, resulting in two nuclei formed.

Terminology First• Chromosomes- long continuous strand of DNA• Histones- A group of proteins that your chromosomes

are associated with.• Chromatin- loose combination of DNA and proteins,

looks like spaghetti• Chromatid- one half of the duplicated chromosome.• Centromere- the center where sister chromatids are

held together.• Telomere- the ends of DNA molecules and they

prevent the chromosomes from accidently attaching to one another as well as gene loss.

Chromosomes• Long continuous thread of DNA with

lots of genes that regulate your entire body

• Body= 46 chromosomes / 23 pair• In just one cell it is about 3ft long• DNA wraps around proteins called

histones• DNA and histones form chromatin

(looks like spaghetti- interphase)• Chromosomes condense tightly for

mitosis-> duplicated looking like an X.

DNA doublehelix

DNA andhistones

Chromatin SupercoiledDNA

DNA wraps around proteins (histones) that condense it.

• DNA plus proteins is called chromatin.

• One half of a duplicated chromosome is a chromatid.

• Sister chromatids are held together at the centromere.

• Telomeres protect DNA and do not include genes.

Mitosis

• The nucleus and chromosomes go through dramatic changes to create two identical daughter cells.

• 4 Stages- PMAT (Prophase, Metaphase, Anaphase, and Telophase)

Parent cell

centrioles

Spindle fibers

centrosome

nucleus withDNA

Interphase

• Copies DNA, grows, and duplicates organelles.

Remember- the cell has already gone through

Interphase and everything is perfect with the DNA

therefore it can continue on.

Prophase= DNA and proteins condense into tightly coiled chromosomes, nuclear envelope

breaks down, centrioles begin to move to opposite sides, and spindle fibers form.

Metaphase- spindle fibers attach and align chromosomes along the cells equator.

Anaphase- chromatids separate and move to opposite sides of the cell.

Telophase- nuclear membrane starts to form, chromosomes begin to uncoil,

and spindle fibers fall apart.

Cytokinesis- divides the cytoplasm into two identical daughter cells.

– In animal cells, the membrane pinches closed.

– In plant cells, a cell plate forms.

Fill it out!

Videos

• http://www.youtube.com/watch?v=VlN7K1-9QB0

• http://www.pinterest.com/pin/32088216069818262/

Regulation of the cell cycle

• External – Outside the cell– 1. cell to cell contact.

When one cell touches another it stops growing- unknown.

– 2. Some cells send chemical messages telling others to grow.

– Cancer cells– Hemophilia– Growth hormones

• Internal– Inside the cell– A lot of times they are

triggered by external factors

– Kinase and cyclin– Kinase is an enzyme that

transfers phosphates- all over your body but the ones that trigger the cell cycle are called cyclins- proteins involved in the cell cycle.

– a normal feature of healthy organisms– caused by a cell’s production of self-destructive

enzymes– occurs in

developmentof infants

webbed fingers

Apoptosis is programmed cell death.

Cell division is uncontrolled in cancer.

• Cancer cells form disorganized clumps called tumors.

cancer cellbloodstream

normal cell

– Benign tumors remain clustered and can be removed.– Malignant tumors metastasize, or break away, and can form

more tumors.

Carcinogens are substances known to promote cancer.

• Standard cancer treatments typically kill both cancerous and healthy cells.http://www.pinterest.com/pin/32088216069639864/

Sexual Reproduction• Sexual reproduction- the joining of

two specialized cells called gametes– Gametes= sperm and eggs

Asexual Reproduction• Creation of offspring from one parent. • No gamete exchange!• Offspring are genetically identical to parent.• Examples include

– Amoebas– Hydras– Fungi– Bacteria– Archaea– Protists– Sea anemones– Coral– Starfish– Some non-flowering plants

– Strawberry– Onion– Potato

Example 1- Mushrooms (FUNGI)

Hydrashttp://www.youtube.com/watch?v=a5oHMjGqjyo&feature=related

Amoeba

Bacteria

• http://www.youtube.com/watch?v=DY9DNWcqxI4

Sea Anemones

http://www.youtube.com/watch?v=sPwi2QcLKao

Sea Star

Binary fission• Most prokaryotes• Results in 2

identical daughter cells just like mitosis.

parent cell

DNA duplicates

cell begins to divide

daughter cells

Budding- eukaryotes through mitosis

– A new plant growing from cutting the stem.

– Hydra

• Small projection grows on the surface of the parent organism, forming a new organism.

Examples Defined As

bud

Hydra

Yeast

Fragmentation

• Sea Star- parent splits into pieces.

• Flatworms

• The splitting of the parent into pieces that each grow into a new organism.

Examples Defined As:

Vegetative Reproduction

• Strawberries• Potatoes

• Forms a new plant from the modification of a stem or underground structure on the parent plant.

Examples Defined as:

Advantages of Asexual reproduction

• 1. They all can reproduce a lot.• 2. More efficient in favorable environments• 3. They don’t have to worry about attracting

a mate.

Disadvantage of Asexual Reproduction

• 1. Mutation in a population could cause the entire population to die.2. So many at one time can cause competition in food and space.3. Extreme temperatures can wipe out entire colonies.

Your body has 2 types of cells….

• Makes up most of your body and tissues.

• Ex- heart, kidneys, eyeballs, etc.

• DNA in your body cell is not passed on to your children.

• Cells in your reproductive organs.

• Ovaries and testes that develop into sperm and eggs= your gametes.

• DNA is spread to your child.

Somatic Cells / Body Cells Sex Cells / Germ Cells

Your Cells have Autosomes and Sex Chromosomes.

• 23 pairs of chromosomes = 46 total in humans• Get 23 from mom and 23 from dad• Each pair = homologous chromosome = means

having the same structure.• Homologous Chromosomes- two chromosomes,

one from mom and one from dad, that have the same length and general appearance.

• The chromosomes have copies of the same genes but they may differ.

Autosomes

• Chromosome pairs 1-22 • Not related to the sex of the organism.

Sex Chromosomes• Pair number 23• In Humans- XY= male,

and XX= female• They are not

homologous• X chromosome is larger

and carries more genes than the Y, which is smaller and carries fewer genes.

Karyotype – a picture of your chromosomes.

Homologous Chromosomes

Sex Chromosomes

Autosomes

Questions????????????

• What is pair 23 called?• Is it a male or female?• How many total chromosomes are there

total?• Which sex chromosome is always larger?

Find the Homolog……

Answers!!!!

• Chromosome #5

• Chromosome # 12

Sexual Reproduction• The fusion of gametes,

resulting in the genetic mixture of both parents!

Fertilization• The actual fusion of the sperm and the

egg. • When it occurs the nucleus of the egg

and the sperm become one.

Diploid and Haploid Cells

• Cells have two copies of each chromosome. One from mom and one from dad.

• Body cells• 2n• Diploid number in

humans = 46 because 2 X 23 = 46

• Cells have only one copy of each chromosome.

• Gametes / germ cells

• N• Haploid

number in humans = 23

Diploid HaploidEach human egg or sperm has 22 autosomes and only 1 sex chromosome.

Process of Meiosis

• Results in 4 genetically different Haploid Cells• Two rounds: Meiosis 1 and Meiosis 2

– Meiosis 1- divides the homologous chromosomes– Meiosis 2- divides the sister chromatids

• Reduces chromosome number and increases genetic diversity

• Sex Cells or gametes that are dividing.

Homologous Chromosomes and Sister Chromatids-

How do I tell them apart?

• Homologous Chromosomes- – Two separate chromosomes, one from your mom and

one from your dad. – They are the same length and carry the same genes,

but they are not copies of each other.

– Each half of a duplicated chromosome is called a chromatid and together they are called sister chromatids and are held together at the centromere.

Homologous chromosomes

Sisterchromatids

Sisterchromatids

• Meiosis I occurs after DNA has been replicated.

• Meiosis I divides homologous chromosomes in four phases.

• Meiosis II divides sister chromatids in four phases.• DNA is not replicated between meiosis I and

meiosis II.

Prophase 1 of Meiosis-Homologous pairs form-Chromosomes trade genes-Nuclear membrane breaks down-Centrioles move to opposite sides--Spindle fibers assemble--Longest phase-CROSSING -OVER

Why is crossing over important?

• Gives rise to genetic recombination. Genetic material between mom and dad is being exchanged.

Metaphase 1• Homologous chromosomes are aligned in the middle by

spindle fibers.• 23 chromosomes line up along each side of the equator-

some from mom and some from dad. • Each side of the equator has chromosomes from both

parents.• Results in 8,388,608 possible chromosome combinations.

Anaphase 1• Homologous chromosomes separate to

opposite sides of the cell.• Sister chromatids remain attached together.

Telophase 1• Spindle fibers fall apart• Nuclear membrane may reform• Cell undergoes cytokinesis• End result= 23 unique duplicated

chromosomes from both parents

Prophase II

• Nuclear envelope breaks down• Centrosomes and centrioles move to

opposite sides of the cell. • Spindle fibers form

Metaphase II• Spindle fibers align chromosomes along the

cells equator.

Anaphase II

• Sister Chromatids are pulled apart from each other to opposite sides of the cell.

Telophase II• Nuclear Membranes

form around chromosomes

• Spindle fibers fall apart• Cell undergoes

cytokinesis• Results in 4 genetically

different haploid cells.

Review……………..

• Produces 2 genetically identical diploid daughter cells

• Takes place throughout an organisms lifetime

• Involved in asexual reproduction.

• Occurs only in body cells.• Responsible for the growth,

repair, and development in all types of organisms.

• Produces 4 genetically different haploid cells

• Takes place only at certain times in an organisms life cycle.

• Involved in sexual reproduction- DNA is copied once but divided 2X’s.

• Occurs only in sex cells / germ cells to produce gametes.

• Sometimes called “reduction division” because it divides the cells chromosomes by half.

Mitosis Meiosis

• https://docs.google.com/present/view?id=dfh23k67_2220hsfjcdf3