Chapter 3: Cellular Structures and Genetic Control

Question 1

Define cell.

Answer 1

Basic unit of structure and function ini the body

- 3 main components: plasma membrane, cytoplasm, organelles

Question 2

Discuss the plasma membrane.

Answer 2

• Surrounds and gives cell its shape
• Selectively permeable
• phospholipid bilayer
  
  • phosphorus end has charge; polar; water-loving: hydrophilic
  • lipid tails have no charge: non polar; don’t like water
• “fluid mosaic model”

Question 3

Discuss bulk transport.

4 Types

Answer 3

1. Phagocytosis
   - forms a vacuole (arms) that reaches out and grabs the object and brings it into the cell for digestion
   - ie. Macrophages and WBC
2. Pinocytosis (type of endocytosis)
   - NON-SPECIFIC!
   - cell furrows inward instead of reaching out
   - can engulf large molecules
3. Receptor-Mediated endocytosis
   - SPECIFIC!
   - Just like pinocytosis but uses receptor proteins to take in specific molecules/compounds from outside the cell
4. Exocytosis
   - export products out of the cell; opposite of pinocytosis

Question 4

Discuss the cytoskeleton.

Answer 4

• It is a latticework of primarily microfilaments and microtubules filling cytoplasm
• maintains shape
• made up of microfilaments and microtubules
• forms tracks to move things around the cell

Question 5

Discuss lysosomes.

Answer 5

“Garbage men of the cell”

• organelles containing digestive enzymes
• involved in recycling cell components
• involved with programmed cell death
• Lots found in the liver

Question 6

Discuss mitochondria.

Answer 6

“Powerhouse of the cell!”

• energy producing organelle
• have inner membrane, outer membrane, separated by inter membranous space
• inner membrane is folded into cristae
• they contain their own DNA

Question 7

Discuss ribosomes.

Answer 7

“Protein factories”

- synthesizes cell proteins

Question 8

Discuss endoplasmic reticulum (ER).

Answer 8

• system of membranes specialized for synthesis or degradation of molecules
• rough ER has ribosomes
• smooth ER does NOT have ribosomes

Question 9

Discuss the golgi complex.

Answer 9

“Packaging and Shipping”

• vesicles enter from ER, contents are modified, then they leave the cell via exocytosis
• lysosomes and secretory vesicles are formed here

Question 10

Discuss the nucleus.

Answer 10

• Contains the cells DNA
• Contains instructions for making proteins
• enclosed in nuclear envelope which becomes continuous with ER
• Proteins and RNA must be actively transported out of the nucleus (requires energy)
• small molecules can diffuse through pores (no energy required)

Question 11

Discuss gene expression, transcription, and translation.

Answer 11

• Genes are lengths of DNA that code for making RNA
• mRNA carries info for how to make a protein and is transported out of the nucleus to ribosomes where proteins are made

Transcription:

• RNA synthesis
• DNA sequence in a gene is turned into mRNA sequence

Translation:
- mRNA sequence is used to make a protein (occurs in the ribosome)

• Together, Transcription and Translation are called “Genetic Expression”

DNA: Gene
RNA: Protein

Question 12

Discuss RNA synthesis.

Answer 12

• Transcription: RNA synthesis
• Occurs in the nucleus
• Different enzymes unzip DNA, tells it where to start and stop; hormones bind to initiate transcription
• Copying one side of DNA strand and having new base pairs attach

Reminder:

• G pairs with C
• A pairs with U
• Human genome 150,000 different proteins; 1 gene codes for average of 3 different proteins
• Transcription produces 4 types of RNA
  1. pre-mRNA
  2. mRNA - contains code for making protein
  3. tRNA - decodes info of mRNA
  4. rRNA - forms part of ribosome

Question 13

Discuss protein synthesis.

Answer 13

• Protein synthesis occurs in the cytoplasm
• Ribosomes read 3 mRNA bases (“codon”) at a time
• Anticodons are complementary to specific mRNA codons; tRNA carries the amino acid specified by its anticodon
• In a ribosome, anticodons on tRNA bind to mRNA condons
• Ribosomes translate codons into amino acid sequence which forms a protein (Translation)

Question 14

General sequence of transcription and translation.

Answer 14

Genetic information in DNA is TRANSCRIBED into mRNA and then TRANSLATED into a protein.

Question 15

Discuss DNA replication. Including semiconservative replication.

Answer 15

• Cell divides; DNA replicates into 2 identical copies which go into 2 daughter cells.
• Normal DNA base pairings
• Most cells in the body divide divide in this way (mitosis)
• Reproductive cells however divid by meiosis for genetic variation

Semiconservative Replication

• An enzyme unzips the DNA producing 2 free strands of DNA (half of the helix) so new base pairs are attached to each strand producing a copy of the DNA
• Each new copy is 1/2 old DNA and 1/2 new DNA
• “Conserves” 1/2 DNA on each side

Question 16

Know the basic steps of the cell cycle.

Answer 16

1. Interphase:
   - non-dividing phase
   - G1, S, G2 (growth, synthesis of DNA, more growth)
2. Mitosis
3. Cytokinesis

Question 17

Discuss the phases of Mitosis. (4)

Answer 17

1. Prophase
   - Chromosomes become visible and distinct structures
2. Metaphase
   - Chromosomes line up single file along equator and positioned by spindle fibers
   (all 23 chromosomes including 1 sex chromosome XX or XY)
3. Anaphase
   - centromeres split
   - spindle fibers pull each chromatid to opposite poles
4. Telophase
   - cytoplasm is divided (= Cytokinesis)

Produces 2 identical daughter cells

Question 18

Understand chromosome terminology.

Answer 18

Chromosome is:
2 chromatids attached at center by a centromere

The “X” looking chromosome is DNA that has already been replicated so it’s identical on each side.

Question 19

Discuss the 2 ways cell death occurs.

Answer 19

Necrosis: pathological changes kill a cell

Apoptosis: normal physiological response: programmed cell death

Question 20

Define and know the difference between Hyperplasia and Hypertrophy.

Answer 20

Hyperplasia

• growth due to an increase in the NUMBER of cells
• most cells in the body grow like this
• tumors take off this way

Hypertrophy

• growth due to increase in cell SIZE
• ie. increase in skeletal muscle mass

Question 21

Discuss Meiosis.

Answer 21

• Type of cell division occurring in ovaries and testes to produce gametes (ova and sperm)
• Has 2 divisional sequences - DNA replicates once and divides twice

Meiosis I: Unique
Meiosis II: Looks like Mitosis

• In meiosis 1, genetic recombination occurs (crossing over of genetic material) homologous chromosomes PAIR along the equator of cell (rather than singly) and one is pulled to each pole, giving each daughter cell 23 different chromosomes
• In meiosis II, each daughter cell divides and the chromosomes are split into 2 chromatids - 1 goes to each daughter cell (going from 46 chromosomes to 23)
• That’s why Meiosis is also called “Reduction Division”

Question 22

What is the difference in production between Mitosis and Meiosis?

Answer 22

From Mitosis you get TWO identical cells.

From Meiosis you get FOUR different cells.