Bio exam 3

Purine

Adenine, guanine

Pyridines

Cytosine, thymine

How do purines and pyrimidines bond and what do they form?

Hydrogen bonds, base pairs g-c a-t

DNA

Nucleotides → gene → chromosome → genome

gDNA

genomic DNA - stored in the nucleus

mDNA

Mitochondria DNA - specific to the mitochondria

Why do we need to duplicate DNA?

For normal growth and repair of cells

Topoisomerase

Cuts DNA strands at the beginning of the duplication process

helicase

Unwinds the strands of DNA and forms a replication fork

What happens after helicase unwinds the strands?

2 template strands are formed and kept open by binding proteins

Where does synthesis begin on the template strand? New DNA strand?

3’ end on template strand and 5’ to 3’ on new dna

Leading strand

Continuous replication

Lagging strand

Discontinuous, has to wait for helicase

Okazaki fragments

Short sequences of DNA that are formed on the lagging template strand

primase

Adds a short segment of nucleotides called an RNA primer

What happens after DNA is replicated?

-RNA primer is removed and ligase seals nick in DNA strand and joins Okazaki fragments

Semiconservative replication

1 new synthesized and 1 template strand in replicated DNA

Transcription

DNA → RNA

Steps of transcription

1. RNA polymerase attaches to DNA and unzips strands

2. RNA polymerase adds nucleotides to the 3’ end of the RNA molecule

3. Terminator sequence in DNA detaches RNA polymerase

4. RNA exits the nucleus

What is mRNA used for?

protein formation

What does tRNA stand for

transfer RNA

what does rRNA stand for

ribosomal RNA

Translation

RNA —> protein

• converts nucleic acids to function protein

codon

• each 3 bases on an mRNA strand

• corresponds to an amino acid

Steps of Translation

1. mRNA attaches to the
   ribosome

2. Anticodon on tRNA, that’s carrying an amino acid, binds with codon on mRNA

3. Ribosome moves along
   mRNA

4. Second tRNA molecule
   (with anticodon and amino
   acid) binds

5. Amino acids join and tRNA
   leaves mRNA

6. Stop codon is reached and
   polypeptide is released
   from mRNA

   
   
   

   
   

Silent substitution mutation

Has no effect

eg: ThE One Big Fly Had One Red Eye

Missense substitution mutation

One change in nucleotide specifies a different amino acid (SNP)

eg: Thq One Big Fly Had One Red Eye

Nonsense substitution

changes amino acid to a stop codon

eg: The One Big

Insertion mutation

insertion of a codon

eg: The One Big Wet Fly Had One Red Eye

deletion mutation

deletion of a codon

eg: The One Big Had One Red Eye

frameshift mutation

changes all codons downstream of the mutation

eg: The One Qbi gFl yHa DOn eRe dEy

chromosome

DNA is packed into chromatin that further condenses into chromosomes

chromatid

a non duplicated chromosome (one “leg” of the chromosome)

sister chromatids

• the 2 chromatids that form a chromosome

centromere

the center of the chromosome that holds the 2 chromatids together

Interphase

the cell prepares for division

G0, G1, S, G2

G0

if a cell does not need to divide it rests in G0

G1

organelles double

S phase

DNA replicates (sister chromatids form)

G2

protein synthesis for cell division occurs

M phase

mitosis and cytokinesis where actual cell division occurs

Prophase

• 1st step in mitosis

• chromosomes become visible in pairs

• nuclear envelope breaks down

• spindle fibers attach to centromere

Metaphase

• 2nd phase in mitosis

• chromosomes line up in the middle of the cell on the metaphase plate

Anaphase

• 3rd step in mitosis

• chromosomes are pulled apart in opposite poles of the cell

• sister chromatids separate and each chromatid is now called a daughter chromosome

Telophase

• 4th step in mitosis

• 2 distinct cells form

• nuclear envelope reforms

Cytokinesis

• after telophase

• division of cytoplasm and organelles

  • cell plate in plants

  • cleavage furrow in animals

What happens if cytokinesis does not occur?

cells remain multinucleated

• this is what happens to skeletal muscle cells

checkpoints

• used to monitor cells with damage or are not functioning properly

• checkpoints at G1, S phase, G2, and metaphase

Apoptosis

• programmed cell death

• Happens if cells do not meet criteria for a checkpoint to reproduce

What happens if cells fail to undergo apoptosis?

They may become cancerous