DNA Replication

Deoxyribonucleic acid (DNA) is a type of Nucleic acid.

RNA

RNA, or Ribonucleic acid, is another type of nucleic acid. Unlike DNA, it is 1 stranded. it is also found in the cytoplasm instead of the nucleus. DNA's nitrogen bases are Adenine, Thymine, Cytosine, and Guanine. However, in RNA, the Thymine is replaced with Uracil. Another difference is that DNA is self-replicating, but RNA is created by a template of DNA.



DNA

Every cell in your body has the exact same copy of DNA. It will copy itself trillions of times using half of the original molecule as a template. First, here is some basic knowledge of DNA structure:

DNA is made up of strings of nucleotides.
A nucleotide is composed of a :

• 5- carbon sugar molecule that is also known as a pentose sugar
• a phosphate group
• nitrogen-containing/nitrogenous base

 

 

 

 The 5-carbon sugar molecule and the phosphate group bond together to form the backbone of the DNA molecule. They create two parallel ones on each side creating the double helix. They both run anti parallel to each other which means they run opposite ways. A double helix resembles a twisted ladder.
 
There are four types of nitrogen bases:        

 

       1        Adenine

2.       Guanine

3.       Thymine

4.       Cytosine

These make up the middle of the DNA molecule.
 Adenine is always paired with Thymine and
   Cytosine is always paired with Guanine
   
 
 

The nitrogen bases are connected by a hydrogen bond.



The enzyme Helicase "unzips your genes" or breaks this hydrogen bond.
The point where the replication starts is called the Replication Fork. The top strand is knows as the Leading strand while the bottom strand is known as the Lagging strand.

The Leading strand and the Lagging strand get their names because the leading is simpler to copy and the lagging is more difficult. In the Lagging strand, the enzyme DNA Polymerase adds matching nucleotides along the molecule. However, before it can start it needs a primer or something to hook on to. That is where RNA Primase comes in. It adds a primer in the beginning by adding the matching base pairs for a few and then DNA Polymerase can start down the molecule.
 On the Lagging strand the process is more complex. DNA Polymerase can only build on strands that are in [5'-->3'] (5 prime to 3 prime) direction and since each sugar phosphate side is antiparallel to each other, the Lagging strand is in the [3'-->5'] (3 prime to 5 prime) direction. For this, RNA Primase has to lay down an occasional short little RNA primer to give polymerase a starting point to work backwards along stand. They work in 1000 to 2000 base pair long segments. These segments are called Ozaki Fragments. After this, DNA Polymerase has to go back and replace RNA primers. Then, the fragments get joined up by an enzyme, DNA Ligase.

DNA replication gets it wrong about 1 in every 10 billion nucleotides. DNA Polymerase also proofread, removing nucleotides from an end of a strand when they discover a mismatched base.

And this is how DNA replicates......

Darwin's Theory of Evolution

                                                Darwin’s Theory of Evolution

            Charles Darwin contributed most to our understandings of evolution. Darwin set sail from England to voyage around the world in 1831 at age 22. During his trip Darwin made many observations and collected lots of information to propose a revolutionary hypothesis about life changes over time. His hypothesis became the theory of evolution. Whenever his ship landed Darwin collected many plant and animal specimens so that he can analyze when he was back on the sea waiting to set foot on another land. Darwin was astonished by the fact that that many of the plants and animals were well suited for the environment in which they were living in. Darwin was also puzzled by the fact that one animal that lived in one climate did not also live on a land with the exact same climate and land vegetation. On his voyage Darwin also collected fossils that looked similar to animals that were still around but some of the fossils looked like a creature that he had never seen before. On Darwin’s notes that were found he seemed very interested while at the Galapagos Islands because here two islands relatively close to each other had very distinct climates. Here he noted that the shape of tortoise’s shells were different when they lived in different climates. He also noted that their necks seemed to be adjusted according to where their food was located. Tortoise’s with short necks has their food close to the ground but tortoises with food a little higher had longer necks to reach their food. Darwin also collected several different types of birds to look at. On these birds he noted that the shapes of their beaks distinct. When Darwin was heading back home to Europe he started to put all of the information that he collected together. After seeing the same type of animal in a different and them looking similar but with different details Darwin came up with the idea that one type of species spread to other lands and evolved to fit certain needs based on food, climate, and land vegetation. In Darwin’s era mostly everybody believed that the earth was only a few thousand years old. When the people from his era heard his hypothesis of Earth’s age they were outraged. Darwin stated that his findings from his voyage could show how people, plants and animals have evolved and how this can simply mean that the earth is old.

Mitosis

The five steps of mitosis, called prophase, prometaphase, metaphase, anaphase, and telophase, constitute the period in which the cell makes preparations for cell division. The five phases are differentiated by specific events of preparation for cell division. Cytokinesis refers to the actual cleavage event, splitting the cell in two.

Mitosis is the splitting and duplication of a cell. Mitosis makes 2 daughter cells, both containing 46 chromosomes.

PROPHASE

Meiosis

MEIOSIS

 

Meiosis is the reduction-division of the chromosomes

- gametes (sex cells)

- haploid [4 daughter cells] = 23 chromosomes each

 

PROCESS OF MEIOSIS

1. Interphase

2. Meiosis I

   * Prophase I - Finds its homologous pair/crossing over occours

   * Metaphase I - Lines up down the "middle" with its tetrad

   * Anaphase I - Split tetrad and they move away from one another

   * Telophase I - Begins to pinch inward to make 2 new cells & nucleus re-forms (cytokinesis)

   * Cytokinesis - Splitting of the cell

3. Meiosis II

   * Prophase II - Nucleus dissolves, spindle fibers form; chromosomes condense

   * Metaphase II - Line up down the middle

   * Anaphase II - Splits the chromatids at the centromere

   * Telophase II - Cells begin to pinch inwards/nucleus reforms

   * Cytokinesis - Splitting of the cell

 

 

Example of crossing over and tetrad



DNA Structures

       DNA Structures

           DNA (Deoxyribonucleic Acids) Store and transmit genetic information. It is made from a String of Nucleotides.

             The Pentagon shape is a five carbon sugar which is deoxyribose. There is a phosphate group which are the circles off to the sides. Lastly there is a nitrogen base ( Adenine, Thymine, Guanine, and Cytosine).

          Adenine is always paired with Thymine

          Guanine is always paired with Cytosine

Both of these bases are connected by hydrogen bonds.

There is a sugar/ Phosphate backbone which make up the outside of the DNA molecule.

  Purines and Pyrimidines

     Adenine and Guanine are the Purines. The pyrimidines are Thymine and Cytosine.

Some people who had some Important discoveries are:

James Watson and Franklin Crick are the men who discovered the double helix.

Another very important person is Rosalind Franklin who devoted her life to finding out as much as she could about DNA structures using x-rays. Her work eventually led to the double helix.

***Remember:  Erwin Chargaff's Base-Pairing Rules:

Adenine pairs with Thymine
Cytosine pairs with Guanine 

These bases pair together because they are similar in chemical composition.

%A = %T
%C = %G

ANIMAL CELL ORGANELLES

1.       Nucleolus

Ø  Inside the nucleus

Ø  The place where ribosomes are assembled

2.       Nucleus

Ø  Contains chromatin or DNA (the protein building instructions)

Ø  Controls the cell

3.       Nuclear Envelop

Ø  Double membrane between nucleus and cytoplasm

Ø  Dotted with thousands of nuclear pores which allows material to move into and out of the nucleus

4.       Ribosome

Ø  Small complexes of RNA and Protein

Ø  Known as the “Factory”

Ø  Sites of protein synthesis (where amino acids connect to each other making a polypeptide chain)

                 

5.       Rough ER (Endoplasmic Reticulum)

Ø  Internal membranes studded with ribosomes which then carry out protein synthesis and exported

Ø  Produces membrane

Ø  Continuous with the nucleus

6.       Smooth ER (Endoplasmic Reticulum)

Ø  Contains enzymes.

Ø  The enzymes produce the synthesis of membrane lipids and detoxify drugs.

7.       Golgi Complex

Ø  Collects packages and sends it to the right place

Ø  Adds carbs

8.       Cell Membrane

Ø  Consists of lipid bilayer with embedded proteins

Ø  Regulates the entrance and exit of substances trying to maintain internal balance

Ø  Protects inner cell from damage

9.       Centrioles

Ø  Help cell when dividing

Ø  They are put to work in both the process of mitosis and meiosis

10.   Mitochondrion

Ø  Generates energy  (ATP) for the cell

Cell Organelles of the Plant Cell by Rebecca Dean

The Plant Cell Organelles

Movement Through the Cell Membrane

Fluid Mosaic Model of the Cell Membrane

Between the inner cell and the conditions of the outer cell stands the cells plasma membrane. It is flexible and not incredibly strong. The lipid molecules of the cell membrane naturally assemble in a double membrane because their tails repel water and their heads attract it. Proteins occur within the lipid molecules. The proteins receive signals from the outside world and they transport nutrients and waste. The molecules located within the cells are constantly moving and changing positions. A semi-permeable barrier around the cell protects the cell because it allows what comes in and what leaves. The barrier acts similar to a border patrol. 

Three things that make up the cell membrane-

1. Lipids

2. Proteins

3. Carbohydrates

Parts to the Cell Membrane

·      Phospholipid Bilayer: Two phospholipid layers

o   Phospholipid bilayer (structure)

o   Carbohydrates (cell identification)

o   Proteins (transport channel)

·      Hydrophilic “Head”: Water liking, attracted to water.

o   Made up of phosphate

·      Hydrophobic “Tail”: Repels water

o   Made up of lipids

·      Passive Transport- is the movement of substances across the cell membrane.

o   What the cell loves

o   Moves back and forth

o   Substances can cross the cell membrane without any input of energy by the cell.

·      Diffusion- is the movement of molecules from an area of higher concentration to area of lower concentration.

o   Moves until it gets to the equilibrium

·      Concentration Gradient- Is the difference in the concentration of molecules across a space.

o   Also moves until it gets to the equilibrium

·      Equilibrium- Is when the concentration of the molecules of a substance is the same Osmosis- is the process by which water molecules diffuse across a cell membrane from high concentration to low concentration.

o   Diffusion stops at the equilibrium

How does diffusion work throughout our cell membrane?

When there is high concentration on the outside of our cell over time it will start to diffuse across Highà Low concentration in the inside of our cell. It will continue to do this until it is balanced. If it becomes too concentrated in the inside of our cell it will diffuse towards the outside of our cell.

·      Three types of Passive Transport

o   Diffusion- high concentrated area à low concentrated area

o   Osmosis- diffusion, but only deals with water

§  It’s the high concentration of water, not sugar, etc.

§  Occurs within our own blood cells

·      Isotonic mediums- perfect balanced (healthy blood cell)

·      Hypertonic mediums- more pure on the inside (unhealthy; causes cell to be damaged)

·      Hypotonic mediums- more pure water on the outside (unhealthy)

o   Facilitative Diffusion- larger molecules use carrier proteins to help them pass through the cell membrane

·      Active Transport

o   Requires Energy

o   Types of active transport

§  Endocytosis- entering the cell

·      Phagocytosis- when cells take in large particles (cell eating)

·      Pinocytosis- when cells take in fluid (cell drinking)

§  Exocytosis- exiting the cell

§  Sodium/potassium pump- pump used to move sodium and potassium ions from low areas of concentration to high concentration

·      Want to actively pump the concentration from the inside to the outside for the sodium ions

·      For the potassium ions we want to have a high concentration on the inside

·      It takes the sodium ions from the inside and loads three of them up into the enzyme. There will be a designated spot for the ions.

·      It takes ATP and drops off one of its phosphates which will allows the enzyme to close.

·      Then the enzyme opens up to the outside and allows the ions to move freely. Which creates a high concentration of sodium on the outside.

·      Then a similar routine occurs with the potassium however only two load up at a time.  

Basic Structure of a Cell Membrane

For more information regarding movement through the cell membrane go to http://www.sophia.org/tutorials/unit-5-movement-throught-the-cell-membrane