Unit 2: Ch 4 (Genetics & Cellular Function)

Question 1

Alternative Splicing of mRNA*

Answer 1

• Process during gene expression that allows a single gene to code for multiple proteins
  
  • Introns are removed (spliced) from the sequence by snRNPs
  • Exons then move out of the nucleus into the cytoplasm

Question 2

Anaphase

Answer 2

• 3rd phase of mitosis
• Activation of an enzyme that cleaves the two sister chromatids from each other at the centromere
• Each chromatid is now a separate, single-stranded daughter chromosome
• Daughter cells are genetically identical

Question 3

AUG Codon

Answer 3

• The start codon
• Code for methionine

Question 4

Base Pairs*

Answer 4

• DNA
  
  • A with T
  • C with G
• RNA
  
  • A with U
  • C with G

Question 5

Base Triplet

Answer 5

• Sequence of 3 DNA nucleotides that stands for 1 amino acid
• Note
  
  • The minimum code to symbolize 20 amino acid is 3 nucleotides per amino acid, which is also the case for DNA

Question 6

Cell cycle

Answer 6

• Interphase
  
  • G₁
  • S
  • G₂
• Mitosis (M)
  
  • Prophase
  • Metaphase
  • Anaphase
  • Telophase

Question 7

Reasons for Cell Division

Answer 7

• Cells…
  
  • Grow large enough to have enough cytoplasm to distribute to their two daughter cells
  • Have replicated its DNA, so it can give each daughter cell a duplicate set of genes
  • Received an adequate supply of nutrients
  • Stimulated by growth factors
  • Have neighboring cells that died, opening up space to be occupied by new cells

Question 8

Chaperone

Answer 8

• As a new protein is assembled by a ribosome, it is often bound by an older protein called a chaperone
• Guides the new protein in folding into the proper shape and helps to prevent improper associations between different proteins
• Also called stress proteins or heat shock proteins because they’re produced in response to heat or other stress on a cell and help damaged proteins fold back into their corrective functional shapes

Question 9

Checkpoints

• Description
• Checkpoint locations

Answer 9

• Description
  
  • At specific checkpoints during the cell cycle, a cyclin binds to a cyclin-dependent kinases (Cdks) and activates a cascade of biochemical reactions that prepare a cell to move on to the next phase of the cycle
• Checkpoint locations
  
  • G₁
  • G₂
  • Metaphase

Question 10

Chromosome Identification*

Answer 10

Question 11

Primary parts of a chromosome*

Answer 11

• Kinetochore: Protein plaque where centromeres attach genetic material
• Centromere: Links a pair of sister chromatids
• Sister chromatids: DNA replication of a chromosome

Question 12

Codon

Answer 12

• A 3-base sequence in mRNA
  
  • When mRNA is produced, it carries a coded message based on DNA triplets
  • The genetic code is expressed in terms of codons

Question 13

How can multiple codons represent the same amino acid?

Answer 13

• Sometimes two or more codons represent the same amino acid
• This is explained mathematically
  
  • Four symbols (N) taken three at a time (x) can be combined in N^x different ways
  • There are 4³ = 64 possible codons available to represent the 20 amino acids

Question 14

Contact inhibition

Answer 14

• The cessation of cell division in response to contact with other cells
• An absence of contact inhibition, leading to uncontrolled cell division, is one of the characteristics of cancer

Question 15

Cytokinesis

Answer 15

• When the cytoplasm is divided into two cells, and the new cells begin interphase
  
  • Cellular division; a cleavage furrow forms around the equator of the cell and the cell eventually pinches in two
  • Overlaps with Anaphase and Telophase phases

Question 16

DNA structure*

• Description
• Components

Answer 16

• Double helix (resembles a staircase)
• Hydrogen bonds
• Components
  
  • Nitrogen base
  • Deoxyribose
  • Phosphorous group
• Notes
  
  • Each sidepiece is a backbone composed of phosphate groups alternating with the sugar deoxyribose
  • The steplike connections between the backbones are pairs of nitrogenous bases
  • The bases face the inside of the helix and hold the two backbones together with hydrogen bonds
  • Across from a purine on one backbone, there is a pyrimidine on the other
  • The pairing of each small, single-ringed pyrimidine with a large, double-ringed purine gives the DNA molecule its uniform 2 nm width

Question 17

Exons & Introns

Answer 17

• Exons
  
  • Portions of DNA required to make a protein
• Introns
  
  • Unnecessary instructions
  • Junk material

Question 18

G-Zero Phase (G₀)

Answer 18

• Cells that “rest” or cease to divide for days, years, or the rest of one’s life
• Cells continue to perform normal functions, but no longer prepare for cell division
• An inability to stop cycling and enter G₀ is characteristic of cancer cells

Question 19

Gap Phase 1 (G₁)

Answer 19

• Occurs before DNA synthesis
• Determines whether conditions are favorable to begin the cell cycle
• Doubles its organelles, and accumulates the materials needed to replicate its DNA

Question 20

Second Gap Phase (G₂)

Answer 20

• Occurs after DNA synthesis
• Checks the fidelity of DNA replication and usually repairs any errors detected
• Cells synthesize the proteins needed for cell division

Question 21

Gene Expression*

Answer 21

Taking DNA instructions and ending up with an outcome

Question 22

Genome

Answer 22

• All genes of a specific organism
• 23 chromosome sets in a human = 46 chromosomes

Question 23

Law of Complementary Base Pairing

Answer 23

• The fact that one strand governs the base sequence of the other
• It enables us to predict the base sequence of one strand if we know the sequence of the complementary strand

Question 24

Meiosis

Answer 24

Cell division mechanism that is restricted to the production of eggs and sperm

Question 25

Metaphase

Answer 25

• 2nd phase of mitosis
• The spindle fibers form a mitotic spindle
• Shortend microtubles form a star-like aster, which anchors the assembly to the inside of the plasma membrane at each end of the cell

Question 26

Mitosis

• Description
• Functions
• Phases

Answer 26

• Description
  
  • Nuclear division
  • Cell division mechanism that serves all functions of cell division, except for the production of eggs and sperm
• Functions
  
  • Development of an individual
  • Growth of all tissues and organs after birth
  • Replacement of cells that die
  • Repair of damaged cells
• Phases
  
  • Prophase
  • Metaphase
  • Anaphase
  • Telophase
• Note
  
  • Can occur without cytokinesis (cellular division) which is why some cells acquire two or more nuclei or multiple identical sets of chromosomes

Question 27

Nitrogenous Bases*

Answer 27

• 1 purine bonds with 1 pyrimidine via H bond
• Purines (2 ring structure)
  
  • Adenine (A)
  • Guanine (G)
• Pyrimidines (1 ring structure)
  
  • Cytosine (C)
  • Thymine (T) - only in DNA
  • Uracil (U) - only in RNA

Question 28

Components of a Nucleotide

Answer 28

• Sugar
• Phosphate group
• Single- or double-ringed nitrogenous base

Question 29

Nucleotide Chain Components in RNA & DNA*

Answer 29

RNA

• Ribose
• 1 of the following nitrogenous bases: U, C, G, A
• Phosphate group

DNA

• Deoxyribose
• 1 of the following nitrogenous bases: T, C, G, A
• Phosphate group

Question 30

Pre-mRNA

Answer 30

• RNA produced by transcription is an “immature” form of RNA, called pre-mRNA
• It contains segments:
  
  • Exons: Will be translated into a protein (exported from the nucleus to undergo translation in the cytoplasm)
  • Introns: Are removed before translation (removed while still in the nucleus)

Question 31

Prophase

Answer 31

• 1st phase of mitosis
  
  • Nuclear envelope disintegrates and releases the chromosomes into the cytosol
  • Spindle fibers form
    
    • Centrioles begin to sprout elongated microtubules called spindle fibers, which push the centrioles apart as they grow
    • The spindle fibers then tug the chromosomes back and forth until they line up along the midline of the cell

Question 32

Proteome*

Answer 32

All the proteins found within an organism

Question 33

RNA Types*

Answer 33

• Messenger RNA (mRNA)
  
  • Transcribes the genetic code from DNA into a form that can be read and used to make proteins
  • Carries genetic information from the nucleus to the cytoplasm of a cell
• Ribosomal RNA (rRNA)
  
  • Located in the cytoplasm of a cell, where ribosomes are found
  • Directs the translation of mRNA into proteins
• Transfer RNA (tRNA)
  
  • Located in the cellular cytoplasm and is involved in protein synthesis
  • Binds amino acids to the ribosome that corresponds to each three-nucleotide codon of rRNA
  • Amino acids then can be joined together and processed to make polypeptides and proteins

Question 34

Synthesis (S) Phase

Answer 34

• DNA synthesis/replication
• Makes a duplicate copy of its centrioles and nuclear DNA
• At the end of the stage, each chromosome consists of two sister chromatids that have identical DNA sequences which remain attached until they are separated during mitosis

Question 35

Stop Codons

Answer 35

• UAG, UGA, and UAA
• They signal “end of message” like a period at the end of a sentence
• Enables the cell’s protein-synthesizing machinery to sense that it has reached the end of the instruction for a particular protein

Question 36

Telophase

Answer 36

• 4th phase of mitosis
  
  • Rough ER produces a new nuclear envelope around each cluster, and the chromosomes begin to uncoil and return to the thinly dispersed chromatin form
  • Daughter chromosomes cluster on each end of the cell
• Telophase is the end of nuclear division but may overlap with cytokinesis

Question 37

Transcription stages

Answer 37

• Initiation
  
  • RNA polymerase binds to a sequence of DNA called the promoter (start codons), found near the beginning of a gene
  • RNA polymerase separates the DNA strands, providing the single-stranded template needed for transcription
• Elongation
  
  • One strand of DNA acts as a template for RNA polymerase
  • As it “reads” this template one base at a time, the polymerase builds an RNA molecule out of complementary nucleotides
• Termination
  
  • Sequences called terminators (stop codons) signal that the RNA transcript is complete
  • Once they are transcribed, they cause the transcript to be released from the RNA polymerase

Question 38

Transcription*

• Description
• List of stages

Answer 38

• The 1st step in gene expression
  
  • DNA → mRNA → Protein
    
    • Purpose is to make RNA copies of individual genes
    • Performed by RNA polymerases, which link nucleotides to form an RNA strand
    • Produces mRNA, tRNA, rRNA, and non-coding RNA
    • Occurs in the nucleus
• Ends when RNA transcript is released and polymerase detaches from DNA. DNA rewinds itself into a double-helix and is unaltered throughout this process
• Note
  
  • → = Codes for the production of

Question 39

Translation stages

Answer 39

• Initiation
  
  • Ribosome joins with the mRNA and the first tRNA so translation can begin
• Elongation
  
  • Amino acids are brought to the ribosome by tRNAs and linked together to form a chain
• Termination
  
  • The finished polypeptide is released to perform its action in the cell

Question 40

Translation*

Answer 40

• 2nd step of gene expression
  
  • DNA → mRNA → Protein
    
    • Protein synthesis from an mRNA template
    • Uses rRNA as an assembly plant, and tRNA as the translator to produce a protein
    • Occurs in the cytoplasm
    • Ends when the ribosome encounters one of the three stop codons; disassembles the ribosome and releases the polypeptide
• Converts the language of nucleotides into the language of amino acids
• Synthesized protein will then:
  
  • Stay in cell & become an instruction for that cell
  • Attach to cell membrane & function as a protein
  • Leave cell to provide instruction to a different cell
• Note
  • → = Codes for the production of