2 Cell Processes and Applications

What are the three steps in the semi-conservative replication of DNA and the enzymes that are used in each?

1. "unzipping" (DNA Helicase)

2. complementary base pairing (DNA polymerase)

3. joining of adjacent nucleotides (DNA polymerase)

What is the result of DNA semi-conservative replication?

Each new DNA molecule created will now contain one original (parental) strand and one newly synthesized strand

What happens during the "unzipping" process of DNA semi-conservative replication?

The enzyme DNA helicase breaks the hydrogen bonds between the complementary base pairs (A–T and C–G) of the DNA double helix.

What is the result of the "unzipping" process during the semi-conservative replication of DNA?

Results in the separation of the two DNA strands, creating a replication fork and exposing the template strands for replication.

What is a replication fork?

The Y-shaped structure formed when DNA is being unzipped during replication

What are the two components of a replication fork?

The leading strand and the lagging strand

What happens during the complementary base pairing process of DNA semi-conservative replication?

The enzyme DNA polymerase guides free DNA nucleotides in the nucleus to the exposed bases on each template strand and ensures they match up correctly (A pairs with T, C pairs with G).

What happens during the joining of adjacent nucleotides process of DNA semi-conservative replication?

The enzyme DNA polymerase forms bonds between sugar and phosphate to create the sugar-phosphate backbone of the new DNA strand, completing the structure.

What are the 3 main purposes for DNA replication?

• Creates identical copies of the DNA molecule for cell division

• Provides a template for repairing damaged DNA

• Facilitate genetic diversity through mutation

Where does DNA replication happen in the cell?

Eukaryotic cells: occurs in the nucleus

Prokaryotic cells: happens in the cytoplasm

What is transcription?

The process of making mRNA from DNA.

What is translation?

The process of using mRNA to build a protein at the ribosome, with the help of tRNA.

What is the role of DNA in the process of transcription?

It stores the genetic code (instructions for making proteins)

Where is DNA found?

In the nucleus of a eukaryotic cell and the nucleoid of a prokaryotic cell

What is the role of mRNA?

it carries the genetic instructions from DNA in the nucleus to the ribosome in the cytoplasm

What happens to mRNA during transcription?

it is synthesized from the DNA template

What happens to mRNA during translation?

The sequence of codons on the ____ tells the ribosome which amino acids to link together and in what order, ensuring the protein is built correctly according to the original DNA instructions.

What is mRNA?

Messenger RNA

What is the role of tRNA?

To delivers the correct amino acid to the ribosome

How does tRNA work?

Anticodons match the codon on the mRNA and carry the specific amino acid to the ribosome to build the protein.

What is the role of ribosomes?

• Read mRNA codons and join amino acids together using peptide bonds.

• The place where proteins are assembled.

What are amino acids?

Building blocks of proteins, which join together to form long chains.

What are peptide bonds?

Chemical bonds that join two amino acids together through dehydration synthesis, forming a peptide or protein chain

What happens during initiation in transcription?

RNA polymerase binds to the promoter region of DNA.

What happens during elongation in transcription?

RNA polymerase builds the mRNA strand, using DNA as a template

What happens during termination in transcription?

RNA polymerase reaches a stop signal (stop codon) and releases the mRNA

What happens during initiation in translation?

Ribosome binds to start codon (AUG) on mRNA. First tRNA binds.

What happens during elongation in translation?

Ribosome reads codons; tRNAs bring amino acids; amino acids are joined.

What happens during termination in translation?

Ribosome reaches a stop codon; protein is released.

What is phospholipids function in the cell membrane?

Form bilayer, acts as a barrier, and has fatty acid tails which allow fluidity

What is proteins function in the cell membrane?

Transport of ions/molecules, communication, structural support

What is glycoproteins function in the cell membrane?

Cell recognition, allowing immune system to distinguish between body and foreign cells. Also signaling and structural support

What is glycolipids function in the cell membrane?

Cell recognition, membrane stability

What is the fluid-mosaic model of the cell membrane?

Describes the structure of the cell membrane

Define hydrophilic

"water-loving" and refers to substances that dissolve easily in water due to their polar or charged nature

Define hydrophobic

"water-fearing" and describes substances that do not mix with or dissolve in water because they are nonpolar and lack charged regions

Which portion of the bilayer is hydrophilic?

phospholipid heads, which face outward toward the watery environments. Found on extracellular and intracellular sides of the cell membrane.

Which portion of the bilayer is hydrophobic?

phospholipid tails, which face inward and forming the inner part of the membrane

What is carbohydrates function in the cell membrane?

Communication, immune function, form glycocalyx

What is Cholesterol function in the cell membrane?

Stabilizes membrane by stiffening and strengthening. Regulates fluidity of membrane.

What is passive transport?

Movement of substances across a cell membrane without the use of cellular energy (ATP)

What is diffusion?

Movement of small, nonpolar molecules (like oxygen and carbon dioxide) directly through the phospholipid bilayer

Direction of diffusion?

high concentration to low concentration

What is osmosis?

The diffusion of water molecules across a selectively permeable membrane.

Direction of osmosis?

Water moves from an area of high water concentration (low solute) to low water concentration (high solute)

What is facilitated transport also known as?

facilitated diffusion

What is facilitated transport?

Movement of larger or polar molecules (ex. glucose, ions) across the membrane through channel or carrier proteins

example of diffusion

oxygen entering a cell or carbon dioxide exiting

example of osmosis

water moving into plant root cells

example of facilitated transport (facilitated diffusion)

glucose entering a cell using a transport protein

What is active transport?

Involves the movement of substances against their concentration gradient — from low to high concentration — and requires cellular energy (ATP)

Proteins involved in active transport:

Carrier proteins or pumps (e.g., sodium-potassium pump)

Function of active transport?

Maintains important ion gradients across the membrane

example of active transport?

Sodium-potassium pump in nerve cells

What is endocytosis?

uses the cell membrane to form vesicles that enclose materials and bring them inside the cell

What are the two parts of endocytosis?

• Phagocytosis

• Pinocytosis

What is Phagocytosis?

Cell eating process where the cell engulfs large solid particles like bacteria or debris. Forms phagosome.

Example of Phagocytosis?

White blood cells engulfing bacteria

What is Pinocytosis?

Cell drinking process where the cell takes in fluid and dissolved substances in small vesicles.

Example of Pinocytosis?

Nutrient absorption in intestinal cells

What is Exocytosis?

The export of large molecules (like proteins or waste) by vesicles fusing with the membrane

Function of Exocytosis?

Used to release hormones, enzymes, or remove waste

Example of Exocytosis?

Release of insulin from pancreatic cells

explain why the cell membrane is described as “selectively permeable”

Because it allows small nonpolar molecules (Oxygen and carbon dioxide) to pass through while blocking large, polar, or charged molecules (glucose or ions) unless they are helped by transport proteins

Temperature effect on rate of diffusion?

• Higher temperature increases the kinetic energy of molecules, increasing the rate of diffusion.

• Lower temperature slows diffusion

Size of molecules effect on rate of diffusion?

• Smaller molecules diffuse more easily and quickly through the membrane.

• Larger molecules move more slowly or may require facilitated transport.

Charge of molecule effect on rate of diffusion?

• Uncharged (nonpolar) molecules pass through the lipid bilayer easily

• Charged molecules = slower diffusion unless helped by proteins

Concentration gradient effect on rate of diffusion?

increased gradient = increased diffusion rate

Pressure gradient effect on rate of diffusion?

• Increased pressure difference across the membrane pushes molecules more forcefully.

• Common in capillaries and lungs where pressure differences aid movement.

Isotonic environment definition?

 solute concentration is equal inside and outside the cell

water movement of an isotonic environment?

Water moves in and out at equal rates (no net movement)

Isotonic environment’s effect on cell?

remains normal in size and shape

What is the ideal environment for animal cells?

isotonic environment

Hypotonic environment definition?

solute concentration is lower outside the cell (more water outside)

Water movement of a hypotonic environment?

Water moves into the cell by osmosis

Hypotonic environment effect on cell?

 swells and may burst (lyse) if too much water enters

Hypertonic environment definition?

solute concentration is higher outside the cell (less water outside)

water movement in a hypertonic environment?

Water moves out of the cell by osmosis

Hypertonic environment effect on cell?

The cell shrinks and shrivels (called crenation)