Science Test Study Guide
Asexual Reproduction
-A new organism is produced that has the same genetic information as the parent.
Several Ways:
1. Mitosis
2. Fission- Mitosis of bacteria
3. Budding- New organism grows from the body of parent. Usually smaller then
grows. Ex/ Hydra
4. Regeneration- Whole organism grows from a piece of an organism. Ex/ Sponge,
some worms
Prokaryotic Cell Cycle
-DNA simply makes a copy and then splits into two cells. Ex/ Bacteria
Mitosis
-Cells divide to produce two identical cells.
-Body cells go through mitosis
Stages of Mitosis
1. Interphase- Divided into 4 phases;
A) G1 phase- “gap” 1- cells increases in size, new proteins and organelles.
B) S phase- “synthesis”, DNA replication (copied)
C) G2 phase- shortest phase, organelles and molecules necessary for cell division
produced
D) M phase- mitosis
2. Prophase;
-Duplicated chromosomes become visible by coiling
-They are connected at the centromere
-Each strand is called a chromatid
-Spindle fibers start to form from the centrosomes of centromeres
-Does not happen in plants (no centrioles)
3.
Metaphase;
-Chromosomes line up in the middle
-Spindle fibers attach to centromere
4.
Anaphase
-Sister chromatids separate to opposite sides
-Pulled by spindle fibers
5.
Telophase
-Cells divide into 2
-Chromosomes uncondensed
-Identical to original parent
Cytokinesis
-In animal cells; Pinching in until 2 cells formed
-In plant cells; Cell plate forms to divide the cell into 2. Cell wall too rigid to
pinch inwards.
The Other Way
-Your body makes two types of cells;
1. Body cells
2. Sex cells- Egg and Sperm (Gametes)
-Human body cells have 46 (Or 23 pairs) chromosomes
-Sex cells have half or 23 chromosomes
Sperm +(Fertilization) Egg=Zygote
23+23=46
Meiosis
-Process by which a cell goes from diploid to haploid number.
2N-->1N N=One set of chromosomes
-Separation of homologous chromosomes
-Creation of gametes (Sex cells)
-Involves 2 divisions
Meiosis I
-Just prior, cell has replicated chromosomes during interphase
Prophase I
-Each replicated chromosomes pairs with homologous chromosomes
-Pairing forms a tetrad
-Undergoes a crossing-over process
-This allows for new combination of genes
Metaphase I
-Paired homologous chromosomes line up
Anaphase I
-Spindle fibers pull homologous chromosomes apart
Telophase I and Cytokinesis
-Two daughter cells formed with diploid (2N)
Meiosis II
-Two daughter cells enter second division
-No replication
Prophase II to Cytokinesis
-Same as meiosis I
-Except 4 daughter cells produced with haploid number (1N)
Mitosis
Occurs in all cells but gametes
One phase (Division)
2 cells formed
Same number of chromosomes as
parent cell
Genetically the same
Meiosis
Occurs when forming gametes
Two phases (Divisions)
4 cells formed
Half the number of chromosomes as parent
cell
Variation from crossing over
DNA
Chromosome Theory
-Hereditary factors (Or genes) are found in chromosomes.
Chromosomes
-Made of DNA (Deoxyribose nucleic acid)
DNA
-Blueprint for an organism’s trait
-The building blocks of DNA are called nucleotides
-Nucleotides are made of three parts;
1. Phosphate molecules
2. Deoxyribose sugar
3. Nitrogenous base
Phosphate
A- Adenine
Base
T- Thymine
C- Cytosine
G- Guanine
Deoxyribose sugar
-DNA is shaped like a double helix (A twisted ladder)
-Made of two strands of DNA
-The double helix is formed by hydrogen bonding between the bases
How does DNA make copies of itself?
-Process called replication
-When chromosomes are duplicated, the amount of DNA is doubled.
1. Helix unwinds with the help of DNA helicase
2. Each strand becomes a pattern for a new strand to form
3. DNA polymerase is an enzyme that joins free nucleotides to the template creating
the new strand.
4. Result- 2 new strands of DNA like the original
A always bonds with T
C always bonds with G
-There will always be the same amount of (A) and (T) or (G) and (C).
RNA
-Puts genetic code into action
-Translates DNA
-Made in the nucleus then goes to ribosomes
-Involved with protein synthesis
-Controls the assembly of amino acids
DNA
Sugar-deoxyribose
Double stranded
Has thymine
RNA
Sugar-ribose
Single strand
Has uracil
3 types of RNA
1) Messenger RNA (mRNA)
-Made from DNA
-Carries instructions
2) Ribosomal RNA (rRNA)
-Make up the ribosomes
3) Transfer RNA (tRNA)
-Translates amino acids to the ribosome needed to make the protein
Transcription
-Process by which segments of DNA produce mRNA
1) RNA polymerase binds to DNA so it unwinds and separates.
2) Promoters- regions of DNA with specific base sequences that tell RNA polymerase
to start.
3) Introns (Junk DNA) from the mRNA are spliced out, leaving behind the exons that
are put back together again.
I Need My Protein!
Translation
-Process by which mRNA makes a protein polypeptide
-Occurs at the ribosome
-Requires 3 nitrogenous bases at a time to decode the code
Codon
-3 nitrogenous bases read at a time.
-Each codon translates into an amino acid
-There are 4 bases which give 64 possible combinations for codons
-Must use a genetic code table to help
-The anticodon is attached to the tRNA that carries the amino acid
-There are start and stop codons
Steps in Translation
1) Ribosome attaches mRNA
2) The ribosome reads each codon and then tRNA brings the appropriate amino acid
3) The start codon is AUG which codes for methionine
4) The ribosome continues translate each codon and peptide bonds from between the
growing polypeptide chain.
5) Stops growing when the ribosome reaches stop codon.
Important Info
When DNA replicated *specific*
Why crossing is very important in meiosis
How DNA translates into proteins