MCAT Biology Draft 2025!

Cell Theory

1. All living things are made up of cells
2. All cells come from pre-existing cells
3. Cells are the basic units of structure and function in living things

4. Cells carry Genetic Information (DNA) in Nucleus

Central Dogma

DNA —> RNA —> Protein

Replication —> Transcription —> Translation (Occurs in Cytoplasm)

Prokaryotic Cell

Reproduce; By Binary Fission

Contains Single circular chromosome

Eukaryotic Cell

Compartmentalization

Organelles Membrane Bound

Have Nucleus

Reproduce; By mitosis

Contain Multiple Linear Chromosomes

Endomembrane System (endo- = “within”)

A group of membranes and organelles in eukaryotic cells that works together to modify, package, and transport lipids and proteins.

• Nuclear envelope

• Golgi apparatus

• Endoplasmic reticulum (ER)

• Vesicles

• Lysosomes

• Vesicle

• Plasma Membrane

Nucleoid Region

DNA region in Prokaryotes

Nucleus

A part of Eukaryotic cell containing DNA and RNA and responsible for growth and reproduction

Nucleolus

Found inside the nucleus and produces Ribosomes

Types of RNA

• mRNA (Messenger RNA): carries genetic information from DNA to the ribosomes for protein synthesis.

• tRNA (Transfer RNA): brings amino acids to the ribosomes during protein synthesis.

• rRNA (Ribosomal RNA): a component of ribosomes, which are the sites of protein synthesis.

Ribosomes

• Site of protein synthesis

Ribosome Sizes

Prokaryotes Ribosomes

70s —> 50/30

Eukaryotes Ribosomes

80s —> 60/40

30 of Prokaryotes and 40 of Eukaryotes is where translation occurs

Endoplasmic Reticulum

• Smooth ER

  • Detoxification

  • Lipid Synthesis

• Rough ER

  • Embedded in ribosomes

  • Accept mRNA to make proteins

A network of membranes involved in protein and lipid synthesis, consisting of smooth and rough sections. Smooth ER is primarily involved in detoxification and lipid synthesis, while rough ER is studded with ribosomes and aids in protein production.

Golgi Apparatus

Package proteins - Protein secretion

Modify / distribute proteins. Only in eukaryotes.

• Put proteins in vesicle and prepare them for execration (being released from the cell)

Mitochondria

Powerhouse of the cell, organelle that is the site of ATP (energy) production

Peroxisomes

Collect and break down material.
Contain oxidase enzymes that detoxify alcohol, hydrogen peroxide, and other harmful chemicals

Lysosomes

Demo & Recycling center. Made by Golgi. Single membrane.
Uses chemicals to break down food and proteins

Cytoplasm

A jellylike fluid inside the cell in which the organelles are suspended

Glycolysis occurs here

Vacuole

a space or vesicle within the cytoplasm of a cell, enclosed by a membrane and typically containing fluid.

Cytosol

Fluid portion of cytoplasm

Centrioles

Located near the nucleus and help to organize cell division
Example: 9 groups of microtubules, pull chromosomes apart

Plasmid

A small ring of DNA that carries accessory genes separate from those of the bacterial chromosome.
In prokaryotes. Carry DNA not necessary for survival.

Cell/Plasma Membrane

• Semi-permeable and made up of Phospholipid Bilayer

• Prefers passing of small, nonpolar, and uncharged polar molecules

• Phospholipid Bilayer

  • 1. Phosphate head 

  • 2. Glycerol Backbone

  • 3. Two Fatty Acids

Fluid Mosaic Model

Fatty acids

Long Hydrocarbon Chains that are key components of Lipids

Plasma Membrane Parts

Amphipathic - Have both hydrophilic and hydrophobic
Phospholipids Bilayer - Phosphate head and two Lipid tail.

Micelles

Lipid molecules orient with polar (hydrophilic) head toward water and nonpolar (hydrophobic) tails away from water

Liposome

Small membrane bounded transport vesicles
Have been used as a drug delivery recently

Cholesterol

Helps Phospholipid bilayer lubricate when it's cold and glues phospholipid together when its hot.

Glycolipid

A lipid covalently attached to a carbohydrate Plasma membrane

Glycoprotein

A protein with one or more covalently attached carbohydrates in Plasma membrane

Membrane Proteins

Integral proteins and Peripheral proteins

Peripheral Proteins

The proteins of a membrane that are not embedded in the lipid bilayer; they are appendages loosely bound to the surface of the membrane.

Integral Proteins

Embedded the hydrophobic interior of the lipid bilayer

Examples of Hydrophobic Molecules

O2, CO2, N2, benzene, lipids and cholesterol

Example of Small Unchanged Hydrophilic (polar)

Urea, Glycerol H2O

Examples of Large Hydrophilic (Polar) Molecules

Glucose and Sucrose

Examples of Ions

H+, Na+, K+, Ca2+, Cl-, Mg2+, HCO3-

Simple Diffusion

Doesn't require energy, depends on concertation gradient
Direct transport of molecules across the cell membrane
Small uncharged molecules or lipid soluble molecules pass between the phospholipids to enter or leave the cell, moving from areas of high concentration to areas of low concentration

Facilitated diffusion

Osmosis

Diffusion of water through a selectively permeable membrane

Hypotonic Solution

Cell is in a solution that is less concentrated than it self.
H2O rushes into the cell to neutralize it, cell might burst process called cytolysis OR swell

Isotonic Solution

A solution in which the concentration of solutes is essentially equal to that of the cell which resides in the solution

Hypertonic Solution

Cell is in a solution that is more concentrated than it self.
H2O get's out of the cell to neutralize it the outside, resulting cell to shrink

Passive Transport

the movement of substances across a cell membrane without the use of energy by the cell
High to low

Active Transport

Energy-requiring process that moves material across a cell membrane against a concentration difference
Low to high

Secondary Active Transport

Form of active transport which does not use ATP as an energy source; rather, transport is coupled to ion diffusion down a concentration gradient established by primary active transport.

We use ATP to create concentration gradient of Na+. Since we used energy to create Na+. We use the energy from this later on to to transport something else like Glucose

Why is it helpful to give Glucose, water and Sodium to someone who is dehydrated? why not just water?

Water alone doesn't get absorbed at a fast enough rate, but with Glucose and sodium they are absorbed together into the cell in the intestines. The concentration of the intestines will be high and now water will rush into the intestines through osmosis.

Solubility of Vitamins

Fat Soluble, Not water Soluble
Vitamin K
Vitamin A
Vitamin D
Vitamin E
Mnemonic: KADE
Vitamin C is not water Soluble, it's found in orange juices

Why is it harmful to drink Salt Water?

Dehydrate you more
Sea water has a high osmatic pressure, causing water to flow out of body cells into the intestines.

Proteins that are used to transport things inside Plasma Membrane

1. Pores
2. Channels
Pores and channels are passive transport
3. Carries - can be Active and Passive Transport

Pores

Holes that allow water to flow through
Can't be open/ closed, They can only be added or remove them
Aquaporins are an examples of pores

Aquaporins

Water channel proteins
Regulated by adding/subtracting the number of pores in membrane.
Example: Add pores if want to make the PM more permeable to water and vice versa.

Channels

Can be opened/ closed
Regulated by
Voltage gated (charge)
Ligand Gated
Mechanically Gated - mostly found in heart

Carries

Change conformation
Can be saturated
Have Enzyme Kinetics - Km and Vmax
Can be inhibited/competitive inhibitors and etc
Can be Active and Passive Transport

Types of Carries

1. Uniporter
2. Symporter
3. Antiporter

Uniporter

Transport one thing at a time

Symporter

Transports two solutes at a time in the same direction

Antiporter

Transports two solutes at a time in the opposite direction. Example: Na+ and K+ ATPase. 2K+ in 3Na+ out. requires energy.
Requires input of energy Uses energy from ATP.

Action Potential

Cell typically hover around -70V
A lot sodium outside and overall charge of the cell is negative

Cells are usually at Resting Potential -70V, it gets a signal. Sodium channels open, more of Sodium Channels open.
Sodium flows into the cell, Na+ channels close and Ka+ opens
Action potential doesn't fire all the time, enough channels must be open in order to fire.

Chloride Channels

Inhibits neuron to fire

Sodium Potassium ATPase

2 K+ In
3 Na+ out

Neuron (Nerve Cell) Structure

Cell Body
Axon
Axon Terminal
Dendrites
Axon Hillock
Myelin sheath
Nodes of Ranvier

Neuron Types

Multipolar, bipolar, unipolar

At Which part of Neuron are the various excitatory and inhibitory signals summed together.

Axon Hillock

Connections between Neuron

Dendrites - beginning of a Neuron
Axon Terminal is end of old Neuron

Synapses

Dendrites - beginning of a Neuron
Axon Terminal is end of old Neuron
When Dendrites and axon hillock come together it's synapses

Synaptic Cleft

The space between when two Neurons coming together
presynaptic neuron and Post synaptic

Signal Termination

1. Degradation - Degrades neurotransmitter
2. Reuptake - back to presynaptic neuron
3. Diffusion -

Pathway of Sperm

Mnemonics: SEVEN UP

Seminiferous tubules —> Epididymis —> Vas deferens —> Ejaculatory duct —> Nothing —> Urethra, Penis

Female: Vagina —>cervix —> uterus —>fallopian tube.

Fertilization in women occurs in Fallopian tube.

When muscles in the skin contract and cause the hair of an animal to “stand on end,” the skin could be functioning as a regulator of:

Body temperature.

Albumin is the major blood osmoregulatory protein. The most likely effect of a sharp rise in the level of serum albumin is:

An influx of interstitial fluid into the bloodstream.

Chromosomal Duplication

Study of Meiosis

During prokaryotic protein synthesis, translation begins as soon as the newly synthesized mRNA strand begins to extend from the DNA strand. This situation differs from that in eukaryotes, because eukaryotes:

Localize the processes of transcription and translation in the nucleus and cytoplasm, respectively.

DNA Replication

Poly A tail - help mRNA travel from nucleolus to Cytoplasm without getting degraded

5 cap - is where translation begins. Ribosome recognizes this site. attaches and looks for AUG start Codon.

For Prokaryotes

The shine dalgarno sequence - same thing as 5cap. Ribosome attaches and does its translation

After the gall bladder is removed from a patient, the patient will most likely have reduced ability to digest: Fat

The gall bladder stores bile produced by the liver and secretes it into the small intestine as needed. Bile acts as an emulsifier, facilitating fat digestion. When the gall bladder is removed, a patient will have reduced ability to digest fats.

In the human "knee-jerk" reflex, the knee is struck and the lower leg jerks forward. Which of the following represents the complete pathway that the nerve impulse travels in effecting this response?

Sensory neuron and Motor Neuron The knee-jerk reflex is a simple monosynaptic stretch reflex. A tap to the tendon that connects the quadriceps to the patella activates a sensory neuron that directly synapses with a motor neuron in the spinal cord, causing the quadriceps to contract.

Reflex Arc

Super fast

Sensory Neuron, Motor neuron Uturn

Doesn’t reach Brain

Synthesis of antibody proteins in eukaryotic cells is associated with what organelle?

As secreted proteins, antibodies are translated by ribosomes attached to the rough endoplasmic reticulum.

Actin filaments within cells can be identified experimentally by the use of a labeled molecule that binds specifically to actin and not to other cell substances. Which of the following would be best to use as the labeled molecule?

Myosin binds to actin during contraction and will remain bound until phosphorylated by ATP. Actin filaments can be “decorated” with portions of the myosin molecule. Although ATP provides energy for muscle contraction, it provides energy for many other cell activities as well and would therefore be nonspecific. In addition, ATP binds to myosin, not to actin, in the contraction cycle. Albumin is a protein found in blood plasma. Myoglobin is the oxygen-binding pigment in muscle. Neither of these molecules is likely to have any specific affinity for actin.

Myosin

Myosin binds to Actin in order to contract muscle

Hardy Weinberg Equations

A set of equations used to calculate allele and genotype frequencies in a population under certain conditions, assuming no evolution occurs.

Germ Layers

Ectoderm

Mesoderm

Endoderm

Ectoderm

Mesoderm

Endoderm

Bacteria

Viruses reproduce by replicating within a host cell and thus cannot be said to reproduce by fission, as bacteria do. Many bacteria do have rigid cell walls, but many viruses have rigid capsids, so the presence of a rigid outer covering does not distinguish the two. Neither bacteria nor viruses have a nuclear membrane and both bacteria and viruses can contain RNA and protein. Thus, the best distinction between a bacterium and a virus is reproduction by fission, answer choice A.

Viruses

Viruses reproduce by replicating within a host cell and thus cannot be said to reproduce by fission, as bacteria do. Many bacteria do have rigid cell walls, but many viruses have rigid capsids, so the presence of a rigid outer covering does not distinguish the two. Neither bacteria nor viruses have a nuclear membrane and both bacteria and viruses can contain RNA and protein. Thus, the best distinction between a bacterium and a virus is reproduction by fission, answer choice A.

HIV (human immunodeficiency virus)

is a retrovirus, an RNA virus that can insert itself into the human genome. This virus can reproduce in host cells because it contains

The question states that HIV is a retrovirus. For the virus to reproduce itself in host cells, its RNA must be converted to DNA, which requires the enzyme reverse transcriptase.

Lung Airway Pathway

Air travels through the nose and mouth through the pharynx. It then flows through the larynx and the trachea before entering the bronchi. The bronchi branch into the bronchioles and finally terminate into the alveoli, where gas exchange can take place between the lungs and the blood stream.

Alveoli

Red blood cells

Do not have organelles, because of they carry Oxygen

Macrophage

Erythrocyte

Osteoblast

Osteoclast

Endocytosis

Exocytosis

Translation of antibody proteins in eukaryotic cells is associated with what organelle?

The stem asks which of the organelles listed is associated with the translation of antibody proteins. Of the organelles listed, only the endoplasmic reticulum is associated with translation of proteins. Synthesis is accomplished by the ribosomes, which are associated with the endoplasmic reticulum. The nucleus contains the genetic information, the mitochondria are involved in cellular respiration, and the Golgi apparatus is involved in the processing and/or export of proteins. Therefore, the key is C.

Antidirutic Hormnes