bio test 2

Chromosomes (how are they packaged, where are they found, what is it not being used for)

They are tightly packaged DNA

Found only during cell division

DNA is not being used for macromolecule synthesis

Chromatin(how are they packaged, where are they found, what is it being used for)

Unwound DNA strands

Found during interphase

DNA IS being used for macromolecule synthesis

How is DNA organized

• Organized into chromosomes

• Double Helix molecules wrapped around histone proteins

• (chromatin are the unwound strands of DNA, chromosomes are the DNA strands that are wound together)

What is a chromatid

• One half of a duplicated chromosome

What is a centromere

• It holds together the sister chromatids

• Does kineotochore formation

• Pairs homologus pairs together

What is a kineotochore

Protein structure that assembles on the centromere and links chromosomes

(handles that the spindle fibers grab onto when pulling the sister chromatids apart during mitosis)

What are the 4 phases of a cells life

• Interphase (cell stil grows and makes proteins/organelles):

  • G1

  • S (replicates DNA)

  • G2

• Mitosis

What happens in the G1 stage

• Beginning of a cell’s life cycle

• Comes right after cytokinesis

• Cell begins growing to full size

• Makes proteins

• DNA is single stranded

What happens in the S phase

• The DNA replicates

• The number of chromosomes stays the same but the number of chromatids double

What happens in the G2 Phase

• Makes the proteins needed for divison

• Checks for errors

what are the stages of mitosis

• PMAT

• Prophase

• Metaphase

• Anapahse

• Telophase

What happens in prophase

• The loose chromatin condense and the chromosomes have the X shape with 2 sister chromatids

• Nucleoli and nuclear membrane breakdown

• The centrosomes move to the opposite side of the cell

• No more DNA is made

What happens in pro-metaphase

• The spindle fibers (microtubules) connect to the chromosomes

What is metaphase

• The chromosomes all line up (metaphase plate)

What happens in anaphase

• Sister chromatids seperate at the centromere

• No longer X shape

• Each is its own chromosome

• Spindle fibers pull them apart

• Each gets pulled to a different side of the cell

What happens in telophase

• The nuclear membrane reforms around the two chromosomes

• The chromosomes unwind (back into chromatin)

• Cytokinesis is already underway(cell is physically dividing)

Cytokinenis in animals

• The cell membrane pinches in on itself

• Cleavage furrow

• Eventually seperates into two daughter cells

Cytokinenis in plants

• A cell wall is formed between the daughter cells (still in 1 cell)

Overview of mitosis (before and during)

• IPMAT

• Interphase

• Propahse (pro-metaphase)

• Metaphase

• Anaphase

• Telophase

What are cyclins

• Proteins mean the cell is ready to move on to the next stage

What is apoptosis

• The programmed process of a cell dying

• Caused by:

  • harsh environment

  • exposure to viruses

  • signals from other cells

• Process called “blebs”

What is cancer

• Uncontrolled mitosis

• Forms tumors

• Cells that don’t die

Asexual reproduction

• No meiosis/ fertilization

• Offspring are usually identical to parent and other “child” cells

• Mitosis

• One parent

• 1 cell becomes 2

Sexual Reproduction

• Use of sex cells (gametes)

• Fertilization to become a zygote

• Different from parent cells

• 2 cells become 1

• Gametes have half the number of chromosomes as the zygote

What is a homologus pair

• A pair of chromosome made by 1 maternal chromosome and a paternal chromosome (each has 2 chromatids for a total of 4 chromatidssa)

• Both chromosomes match because they code for the same thing (hair color)

Haploid vs Diploid Cells

• Haploid:

  • Only carries half the regular amount of chromosomes

  • Human reproductive cells (sperm/egg) have 23 chromosomes

• Diploid:

  • Have a regular amount of chromosomes

  • In humans (23 pairs = 46)

What are Autosomes

• Found in male and female

• Humans have 22 pairs

• Contain genetic information

• Homologus pairs (half maternal / half partenal)

What are Sex Chromosomes:

• Determine the sex of an individual

• One pair of chromosomes

  • X and X = Female

  • X and Y = Male

• NOT HOMOLOGUS

• X chromosomes are bigger and contain more information than the Y

What happens in Prophase 1

• Chromatin is condensed into chromosomes

• Chromosomes pair up with their homologus pairs

• Crossing over (genetic information is exchanged between pairs) (first source of genetic variation)

• Centrioles move to poles

• Nuclear membrane breaks down

What happens in metaphase 1

• Chromosomes are arranged on the metaphase plate as homologus pairs

• second source of genetic variation

What happens in anaphase 1

• Homologus pairs are pulled apart

  • One chromosome from the pair is pulled to each side (still as a chromosome) (sister chromatids move to the same pole)

What happens in telophase 1

• Each pole with its haploid chromosomes seperates into its own cell

What happens in prophase 2

• The spindle reforms

• Chromosomes begin moving to the metaphase 2 plate

What happens in metaphase 2

• The chromosomes are lined up on the metaphase plate

What happens in anaphase 2

• Sister chromatids are seperated by the centromeres

• Chromosomes move to opposite poles

What happens in Telophase 2

• Cell splits again

What is independent assortment

• The way in which one pair of homologus chromosomes lines up on the metaphase plane is independent of how the others line up

What are the 4 differences between mitosis and meiosis

1. Meiosis happens in reproductive cells

2. Meiosis has 2 divisions while mitosis only has 1

3. Meiosis results in 4 haploid cells and mitosis results in 2 diploid cells

4. The daughter cells in meiosis are different while the ones from mitosis are the same (due to crossing over and independent assortment)

Differences between male and female meiosis

Male:

• Spermatocytes are made due to testosterone and are made starting during puberty and continue being made forever

• Meiosis is completed before the sperm leave the testes

Female:

• All oocytes are made before birth

• Meiosis is only completed if the egg is fertilized

What is meiotic non-disjunction

Failure of chromosome pairs to seperate properly during cell division

What is aneuploidy

Any chromosome number that is not a multiple of the haploid number

What is trisomy XXX

When a woman is born with three X sex chromosomes

Causes some defects

What is klinefelters

A man has a XXY sex chromosome pair

Causes defects

What is Monosomy (Turner Syndrome)

Females born with only one X sex chromosome

What is trisomy 21

• Down syndrome

• 3 copies of the 21 chromosome (1 extra chromosome)

What are the 4 nucleiotide bases

1. Adenine

2. Guanine

3. Thymine

4. Cytosine

A pairs with T

C pairs with G

What does semiconservative DNA replication

There is a permanent seperation between the two strands of DNA

Each strand is used to make a new template strand

what are the 4 steps of DNA replication

1. Seperation of the strands

2. Short RNA primers are formed

3. Use both strands of DNA as a template

4. RNA is replaced and replication ends

What happens in the first step of DNA replication

replication begins at the many replication bubbles (a lot to speed up the process)
The bubbles move in both directions and copy the DNA as they grow
Once bubbles meet, the process is done

What is the role of Helicase in strand seperation

It unwinds and seperates the DNA strands

What is the role of topoisomerase

relieves tension by cutting the phosphodiester bonds

What is the role of primase

It puts down the short piece of RNA known as a primer

what is the role of DNA polymerase

Reads along the naked strand and adds the complementary nucleotide

What happens in step 2 of DNA replication

Primase attaches to the single stranded DNA and adds a small RNA primer in the 5’→ 3’ direction while moving in the a 3’ → 5’ direction

Why must a RNA primer be added to a single stranded DNA

The DNA polymerase cant start building from nothing, it can only build onto something

The RNA primer gives it a starting point

What happens in step 3 of DNA replication

The DNA polymerase attaches to the RNA primer and produces the complementary strand

What direction does the DNA polymerase moving

what direction does it build the strands in

it moves in the 3’ → 5’ direction

builds the daughter strands in the 5’ → 3’ direction

What is the difference between leading strand and lagging strand

The leading strand is built continuously since it is the strand that is the same direction as the fork (one primer at the start)

the lagging strand is the strand that runs in the opposite direction

it needs a new primer so it can build, these fragments are called Ozaki fragments

What happens in ster 4 of DNA replication

The RNA primers are replaced with DNA

How is the RNA replaced with DNA

Nuclease and DNA polymerase: work to replace the RNA primers

Ligase: forms the phosphodiester bonds between the new DNA and the rest of the DNA

What enzyme proofreads the new nucleotides

DNA polymerase

What are mutations

Mistakes in the replication of DNA

What are telomeres

They are special non-coding nucleotide sequences that are at the end of chromosomes

They erode gradually

What does telomerase do

Telomerase extends the final 3’ end of the lagging strand so that a primer can fit and the synthesis can be completed

What is PCR

What is its role

Polymerase Chain Reaction

It’s the rapid and specific replication of a specific portion of DNA without the need for a cell

What are the three main parts of PCR

1. Denature the DNA

2. Primers Aneal

3. DNA polymerase extends the DNA chain

What are the 2 steps of making proteins/genes

Transcription

Translation

What is the process of transcription

an RNA copy is made from a gene DNA template (this is pre-mRNA) then it is processed(some pieces are removed) and becomes mRNA

what is the process of translation

The ribosomes read the mRNA and builds a specific chain of amino acids (polypeptides)

protein

What are the 4 types of RNA

1. Messenger RNA (mRNA)

2. Ribosomal RNA (rRNA)

3. Transfer RNA (tRNA)

4. microRNA

What is the role of messenger RNA

They code for proteins

What is the role of ribosomal RNA

forms the core of the ribosomes

Makes the proteins

What is the role of transfer RNA

Carriers the amino acid for the growing protein chain

What is a codon

A group of 3 nucleotides that code for a specific amino acid or signal stop and start

What is the sequence of the start codon

AUG

What are the 3 sequences for stop codons

UAA

UGA
UAG

How is RNA translation similar and different from DNA replication

Similar:

• Opens and unwinds DNA

• 1 template strands

• Complementary base pairing

Different:

• RNA does not stay paired

• RNA is single stranded

• RNA is shorter

What is the role of RNA polymerase

Catalyzes new phosphodeister bonds
Uncoils the DNA

Adds new nucleotides (5’ → 3’)

Differences between RNA and DNA polymerase

• RNA has ribonucleotides vs DNA deoxynucleotides

• RNA polymerase can’t proofread

• RNA doesnt need a primer

What is the process from Template to transcription

1. A double helix DNA is seperated into 2 strands (template and coding)

2. The template is used to make a complementary mRNA strand that is identical to the coding strand except (T → U)

3. From the mRNA strand the codons are read

What are the 3 stages of transcription

1. Initiation

2. Elongation

3. Termination

What happens in the initation step

1. The promoter contains the TATA box, where the process begins.

2. A transcription factor binds the TATA box, then additional transcription factors join.

3. RNA polymerase binds at the promoter, forming the transcription initiation complex.

4. The DNA unwinds and RNA synthesis begins.

What happens in the elongation step

The RNA polymerase moves downstream

Reads in the 3’ → 5’ direction

Builds in 5’ → 3’ direction

DNA helix reforms behind it

Goes until it reaches a termination sequence

What happens in the termination step

RNA polymerase reads the termination signal (AAUAAA)
pre-mRNA is released
Enzymes modify the ends (5' cap and poly(A) tail)

what is RNA splicing:

• making the pre-mRNA into mRNA

• removes the introns (non-coding sections)

• Splices the exons together

What is responsible for the removal of introns and splicing of exons

snRNPs (small nuclear riboprotein particles)

Benefit of splicing

Genetic recombination

What is the role of the large subunit of a ribosome

Catalyzes the formation of the peptide bond

What is the role of the small subunit of a ribosome

Matches the tRNA to the mRNA

what are the 4 binding sites on a ribosome

1. mRNA

2. Peptidyl-tRNA (P-site)

3. Aminoacyl-tRNA (A-site)

4. Exit (E-site)

2,3 and 4 are on the large subunit

What are the 4 types of gene mutations

1. Silent

2. Missense

3. Frameshift

4. Nonsense

What is a silent mutation

Mutation with no effect

third nucleotide is changed but doesnt change the amino acid

What is a missense mutation

Subsitution of a nucleotide causing a new amino acid

What is a frameshift mutation

Addition/deletion of 1 or moew nucleotides

Competely new amino acid

What is a nonsense mutation

Formation of a stop codon in a place where a coding codon should be

What are the 4 types of chromosomal mutation

1. Deletion

2. Duplication

3. Inversion

4. Translocations

What is a deletion mutation

Loss of a portion of the chromosome

(can be compensated for by the homologus pair)

What is a duplication mutation

A region of a chromosome is represented twice

(can facilitate evolution)

What is an inversion mutation

A portion of the chromsome is removed, rotated or replaced

What is a translocation mutation

A portion of the chromosme being placed on the other homologus pair