The Mitotic Cell CycleWith Cancer and Stem Cells

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Gamete: a mature reproductive cell with half the number of chromosomes e.g. egg/ sperm cell

Homologous pair: A pair of chromosomes that code for the same type of proteins

Haploid: n copies of Chromosomes or half the usual number

Diploid: 2n copies of chromosomes or the full set of chromosomes

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When two haploid cells fuse – they form a diploid cell

That diploid cell called Zygote divides by mitosis

After which they can differentiate into different cells

Some of the cells differentiate into germ cell and become the gonads

CHROMOSOMES CHROMATINCHROMATID

The structures of Chromosomes

Chromatin

Referred to as the loosely coiled form of chromosomes during the interphase of the cell cycle

Chromatin is a complex of DNA and proteins that forms chromosomes within the nucleus of eukaryotic cells

DNA + Structural protein that gives it the shape

DNA molecules are wrapped around histone protein

ChromatidReferred to as one of two identical

parts of chromosome, held together by a centromere, formed during interphase by the replication of DNA strand

A well defined chain of DNA already fully formed with histone protein

each of the two threadlike strands into which a chromosome divides longitudinally during cell division. Each contains a double helix of DNA.

Chromosome

A threadlike structure made of DNA and histones, found in the nucleus of a eukaryote

The Structure of a Chromosome

The Structure of a Chromosome

Made up of 2 chromatids – made up of coils called chromatins, made up of DNA structure tied around the histone protein also coiling up.

Joined by a centromere – found anywhere along the chromosomes

The ends are the telomeres

Centromere

Is needed as it is the site of attachment for the spindle microtubules

Known to hold the chromatids together

Different in every chromosome – has an identification quality

Kinetochore

Construction of this particular part starts in the S phase before they are lost afterward

Made of protein molecules – can bind with the DNA in centromere – and also the microtubules

The microtubules extended from the Kinetochores to the poles of the spindle

Centrosome/ Centrioles

Centrosomes act as the MTOCs during mitosisThere are proteins there that produce the

spindleCentrioles did jack shit.

CELL CYCLE

Importance of Mitosis

Growth – through the multiplying cellsReplacement of cells – replacing the cells that

diedRepairing tissues Immune responses – cloning of t, B lymphocytesAsexual reproduction – eg. For unicellular

organism or budding in plantsVery important in genetic engineering

The Cell Cycle

The Cell Cycle

CELL DIVISION: Mitosis: The division of the nucleus – nuclear division Cytokinesis: Division of the cell itselfINTERPHASE: G1 phase: Growth – cellular content being duplicated – make

RNA, Enzymes S phase: receives signal - DNA is replicated G2: continues to grow - gets ready for another replication –

DNA is checked for any error – increase in the production of tubulin

The many phases of Mitosis

ProphaseMetaphaseAnaphaseTelophase

Prophase

1. Early Prophase Centrosome is already replicated Chromosomes first condense – shorter and thicker2. Late Prophase Nuclear envelope fragments – breaks up into small vesicles Nucleolus disappears – chromosomes are already

dispersing Chromosomes have 2 identical chromatids Centrosomes are now moving to either side

Metaphase

The Chromosomes line up in the middleThe centrosomes have fallen into their places

– the production of microtubules beginSpindle are produced

Anaphase

Microtubules extending between kinetochore and centrosome becomes shorter

Chromatids pulled to the opposite poles by the microtubules

Centromeres are pulled first (kinetochore already bind with microtubule)

Telophase

Nuclear envelope reformsChromatids uncoilingRemains of the spindle breaking downNucleolus reformingCell being pinched in half In plant cell: A cell plate is formed between

the 2

Importance of Telomere

Telomere sealed the ends of the chromosomes Made of DNA with short base sequences, repeating

many times – no useful information They make sure the end of the DNA molecules are

not left out during the replication by making them longer – so the last bit of information won’t be left out

Performed by the enzyme telomerase In cells without telomere – those that are

differentiated, the end can be left out, making each new copy of the DNA incomplete – this is theorized to be the cause of ageing.

Stem Cells

A cell that can divide unlimited number of times When one divides it can remain a stem cell or

differentiates. The ability to vary into different cells = potency Can produce any type of cells: Totipotent Cells that can develop into anything that will lead to

the development of the embryo: pluripotent Some lost the ability to even become embryotic cell –

can only produce a few types of cell - multipotent

Totipotent cells

Zygote for example

Some cells specialized

Some cells lost the ability – becoming pluripotent

Pluripotent

Can form all the cells that will lead to the development of the embryo and later the adult

Embryonic stem cells – pluripotent

Basically it can give rise to any cell that forms the body

Multipotency Cells become more committed with its role during adulthood – the cell

loses the ability to divide Some are no longer pluripotent/totipotent They became multipotent Can divide many numbers of times – but only of a specific type of cells Red Blood Cells – an example

Stem Cell Therapy

The introduction of new adult stem cells into damaged tissue to treat disease or injury

Bone marrow transplantation for leukemia for example

Might be able to cure Parkinson’s, Huntington’s diseases

There are still experiments on growing new organs

Cancer

A disease, often but not always treatable, that results from a breakdown in the usual control mechanisms that regulate cell division; certain cells divide uncontrollably to form tumor which may grow into secondary tumor in other areas of the body – metastasis.

CancerCancers = uncontrolled

MitosisCarcinogens: A

substance that can cause cancer

Benign – Tumors that do not spread from its site of origin

Malignant (One that interferes with body function eg. Blocks blood vessel/ intestine)

Cancer

Starts: Mutation that creates an oncogenes (genes that are mutated) – from carcinogen

Usually mutated cell is destroyed – however cancer cells escape detection

Doesn’t respond to signals from the body – just DIVIDE

Tumors get bigger – changes in characteristics Blood vessels and lymph vessels begin supplying

the tumor Invades other tissue – Metastasis – spreads across

the body

Protein SynthesisAnd DNA Replication

Nucleic Acid

Polymer – Polynucleotide1 Nucleotide: Nitrogenous base, pentose

sugar (ribose/deoxyribose), phosphate group

RNA

A single strand made up of nucleotides Ribose Sugar Has a phosphate backbone Nitrogenous bases: Adenine, Uracil, Guanine, Cytosine AT – GC / AU A,G (Purin bases) – T, C, U – (Pyrimidine bases) –

Thymine is a more stable molecule GC – has a triple hydrogen bond

DNA

Made up of NucleotidesSugar: DeoxyriboseDeoxyribose has one less oxygenPhosphate backbone – linked to sugar by

phosphodiester bondThe backbones are anti parallelNitrogenous bases(Adenine, Thymine,

Cytosine, Guanine)

DNA Double Helix

DNA – a double polymer – 2 polynucleotides linked by hydrogen bond spiraling around an imaginary axis

The back bones run opposite – one backbone runs from 5’ to 3’ the other runs from 3’ to 5’

Purine bases – larger molecules (Adenine/ Guanine)

Pyrimidine bases – smaller (Thymine, Cytosine, Uracil)

Uracil replaces Thymine in RNA

Complementary Base Pairing

As you see in the diagram of a DNA – the two polynucleotides strands are connected between the 2 bases

There is a regular pattern in this connectingPyrimidine base will always be paired with

purine basesThe specific pairing are: Adenine always with

Thymine … Cytosine is always with GuanineA-T(or U) G-C

Complimentary base pairing

It is the ordering/ sequences of nitrogenous bases that act as the codes for protein synthesis in each cell

These proteins regulate the shape, function and our bodies as a whole In retrospect: the DNA, through the codes of nitrogenous bases control the

production of proteins and hence control the body function This is done when a strand of DNA breaks off and acts as the order for

protein synthesis For example, the order is a sequence of bases that say Adenine, Guanine,

Adenine, Guanine, Adenine Or AGAGA The response would be the opposite base pairing – TCTCT IT IS THIS RESPONSE THAT CODE FOR A SPECIFIC TYPE OF AMINO ACID THAT

WILL THEN BE RETRIEVED AND FORM INTO PROTEINS

mRNA

Messenger RNAmRNA is made in the nucleusTranscription happens in the

nucleusSometimes the process of

transcription can happen with translation

Put together by RNA Polymerase 2

rRNA

Ribosomal RNAFound in RibosomeAct like an enzymePut together by RNA polymerase 1

tRNA

Transfer RNA3D structurePut together by RNA

polymerase 3 It has an amino acid

sticking to it by an ester bond

Floating all over the cytoplasm

DNA Replication – The Process

DNA always happen in 5’ to 3’ directionWhat we need?1. The DNA2. Enzyme Helicase3. Enzyme Polymerase4. Activated phosphate5. Nitrogenous bases

Steps

1. DNA start creating bubbles – the origin of replication2. Helicase unwinds the DNA3. The nucleotides with extra phosphates are activated4. DNA Polymerase begins synthesizing the strands of

DNA5. The nucleotides join up with their complementary

bases6. The phosphates are then released into the

nucleoplasm

Protein Synthesis

Transcription – DNA makes an mRNA which is a copy of one strand of the DNA

A triplet code codes for an amino acidThe mRNA is then translated into the

sequence of amino acid which makes up a polypeptide

Bibliography

UCBERKELY – BIOLOGY 1A Lecture