MPharm PHA115: Protein Synthesis & Cell Division

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Questions and Answers

What role do proteins play in cells?

They store genetic information needed for cell division.

They solely provide energy for cellular activities.

They help assemble cellular structures and serve various functions such as hormones and enzymes. (correct)

They act exclusively as transporters for nutrients in the cell.

What is the first step in protein synthesis?

Exchange of amino acids in the cytoplasm

Replication of DNA for cell division

Transcription of DNA to RNA (correct)

Translation of RNA into protein

Which statement best describes the significance of somatic cell division?

It enables growth, tissue repair, and maintenance of homeostasis. (correct)

It occurs only during the early stages of embryonic development.

It is primarily involved in the creation of gametes.

It leads to the duplication of genetic material only.

During which process is information from DNA transcribed into RNA?

Transcription Signup and view all the answers

Which component directly carries the signals that induce somatic cell division?

Hormones Signup and view all the answers

What is the primary function of the G1 phase in the cell cycle?

Replicating organelles and cytosolic components Signup and view all the answers

What characterizes diploid cells in somatic cell division?

Contain two sets of chromosomes Signup and view all the answers

During which phase does DNA replication occur?

S phase Signup and view all the answers

What happens to a cell that remains in the G1 phase for a very long time?

It enters the Go phase Signup and view all the answers

How long does the G2 phase typically last?

4 to 6 hours Signup and view all the answers

Which statement about sex chromosomes is true?

Females have two X chromosomes Signup and view all the answers

What is the total cell cycle duration indicated for a typical cell?

24 hours Signup and view all the answers

Which phase follows the S phase in the cell cycle?

G2 phase Signup and view all the answers

What is the primary outcome of meiosis in terms of chromosome number?

Chromosome number is reduced by half Signup and view all the answers

In which type of cells does meiosis occur?

Germ cells Signup and view all the answers

What is the haploid number of chromosomes produced in gametes after meiosis?

23 chromosomes Signup and view all the answers

How many times does the nucleus divide during meiosis?

Twice Signup and view all the answers

What term describes the cells produced by meiosis?

Haploid cells Signup and view all the answers

What main difference distinguishes meiosis from mitosis?

Number of divisions Signup and view all the answers

At what stage of life does meiosis typically occur?

At sexual maturity Signup and view all the answers

Which statement correctly describes the genetic similarity of daughter cells produced by meiosis?

They are genetically diverse from each other Signup and view all the answers

What role does messenger RNA (mRNA) play in protein synthesis?

It serves as a template for protein synthesis. Signup and view all the answers

Which RNA type assists in the assembly of ribosomes?

Ribosomal RNA (rRNA) Signup and view all the answers

What is the function of transfer RNA (tRNA) during translation?

It binds amino acids and delivers them to the ribosome. Signup and view all the answers

What initiates the transcription process on a DNA strand?

A promoter sequence Signup and view all the answers

During transcription, how does RNA polymerase interact with the DNA template?

It uses one DNA strand as a template for RNA synthesis. Signup and view all the answers

What is the complementary RNA base for adenine (A) in DNA during transcription?

Uracil (U) Signup and view all the answers

Where does the translation of mRNA into a protein occur?

In the cytoplasm Signup and view all the answers

What sequence indicates where transcription ends in DNA?

Termination sequence Signup and view all the answers

What is the role of the small sub-unit of a ribosome?

It binds to mRNA. Signup and view all the answers

Which of the following correctly describes the P and A sites on the large sub-unit of a ribosome?

The P site is where the first tRNA molecule attaches. Signup and view all the answers

What characterizes somatic cell division?

It consists of mitosis and cytokinesis. Signup and view all the answers

During which process is the number of chromosomes in a cell reduced by half?

Meiosis Signup and view all the answers

How many pairs of chromosomes do human somatic cells typically contain?

23 Signup and view all the answers

What is the purpose of somatic cell division?

To repair and replace dead or injured cells. Signup and view all the answers

What are homologous chromosomes?

Chromosomes that have similar genes arranged in the same order. Signup and view all the answers

What distinguishes reproductive cell division from somatic cell division?

Reproductive cells undergo a special two-step division. Signup and view all the answers

What happens to the original DNA molecule after replication?

It becomes two identical DNA molecules. Signup and view all the answers

What role do cyclins play in the cell cycle?

They drive the cell through various phases. Signup and view all the answers

What primarily controls the cell cycle at checkpoints?

Chemical signals Signup and view all the answers

Which process ensures that cell division is initiated correctly?

Kinase enzyme action Signup and view all the answers

What is a major component of the 'Go-ahead signal' in the cell cycle?

Growth factors Signup and view all the answers

What does MPF stand for in the context of cell division?

Mitosis Promoting Factor Signup and view all the answers

In what type of reproduction do gametes from two different parents unite?

Reproductive cell division Signup and view all the answers

What is the function of checkpoint control systems in the cell cycle?

To ensure key processes have been completed correctly Signup and view all the answers

Which statement about the genes for regulatory proteins in the cell cycle is true?

They are highly conserved through evolution. Signup and view all the answers

Study Notes

MPharm Programme: Protein Synthesis and Cell Division

Course name: Protein Synthesis and Cell Division
Course code: PHA115
Lecturer: Dr Praveen Bhugra

Learning Objectives

Students should be able to describe the sequences of events in protein synthesis, including gene expression, transcription, and translation.
Students should be able to understand and explain the stages and significance of somatic and reproductive cell division.
Students should understand and describe the signals that induce somatic cell division.

Introduction to Protein Synthesis

Cells synthesize many chemicals to maintain homeostasis.
Cellular machinery is devoted to producing large numbers of diverse proteins.
Proteins determine the physical and chemical characteristics of cells.
Proteins assemble cellular structures (plasma membrane, cytoskeleton, organelles), act as hormones, antibodies, and contractile elements in muscles.
Other proteins are enzymes, that regulate chemical reactions in cells, and transporters that carry materials in the blood.

Introduction to Protein Synthesis (continued)

DNA serves as a template for protein synthesis.
Transcription: Information from DNA is copied into RNA.
Translation: RNA information is used to synthesize a protein.

Transcription

Three types of RNA are made from DNA: mRNA, rRNA, and tRNA.
mRNA directs protein synthesis.
rRNA joins with ribosomal proteins to form ribosomes.
tRNA binds to amino acids and holds them in place on a ribosome until incorporated into a protein during translation.

Types of RNA Produced in Cells

mRNA: codes for proteins
rRNA: forms the core of ribosomes and catalyzes protein synthesis
miRNA: regulates gene expression
tRNA: serves as adaptors between mRNA and amino acids during protein synthesis
Other small RNAs: participate in RNA splicing, telomere maintenance, and other processes

Transcription (continued)

Enzyme RNA polymerase catalyzes DNA transcription.
Only one DNA strand is used as a template for RNA synthesis.
Transcription begins at a promoter (a specific nucleotide sequence).
Transcription proceeds in a complementary manner.
Transcription ends at a terminator (a special sequence).

Translation

The nucleotide sequence in mRNA specifies the amino acid sequence of a protein.
Ribosomes perform translation in the cytoplasm.
A ribosome has a small subunit and a large subunit with binding sites for tRNA (P site and A site).
The first tRNA molecule with a specific amino acid attaches to mRNA at the P site and the A site.
The A site accepts next tRNA.
Amino acids are linked together forming a peptide bond.
The process continues until a stop codon is reached.

Cell Division

Human cells undergo cell division.
Somatic cell division: all body cells other than germ cells
Reproductive cell division: produces gametes (cells for sexual reproduction)
Somatic cell division replaces dead/injured cells and adds new cells during tissue growth.
Somatic cell division involves mitosis and cytokinesis. This involves nuclear and cytoplasmic division respectively
Reproductive cell division involves meiosis, a special two-step division reducing the number of chromosomes in the nucleus by half.

Somatic Cell Division

The cell cycle is an orderly sequence of events.
Human cells contain 23 pairs of chromosomes (46 total).
Chromosomes that make up a pair are homologous chromosomes, which contain similar genes arranged in similar orders.
Exception to this: the sex chromosomes (X and Y).
Somatic cells contain two sets of chromosomes (diploid).
The cell cycle has two major periods: interphase (when a cell is not dividing) and the mitotic (M) phase (when it is dividing).

The Cell Cycle

Interphase has three subphases (G1, S, and G2).
G1 checkpoint: signals to check the integrity of DNA, growth factors, nutrition and size of cell before entering DNA replication.
S phase: DNA replication occurs.
G2 phase: cell growth continues and protein synthesis occurs in preparation for division.
The mitotic phase consists of mitosis and cytokinesis.
Mitosis has four phases: prophase, metaphase, anaphase, and telophase.

Interphase

G1 phase: interval between the mitotic phase and S phase
Cell is metabolically active; replicates most organelles and cytosolic components, but not DNA. DNA replication of centrosomes starts here.
S phase: Interval between G1 and G2, DNA replication occurs resulting in two identical cells.
G2 phase: Interval between S and mitosis, continued cell growth, synthesis of enzymes and other proteins. Replication of centrosomes is completed.
Original DNA molecule splits into two identical DNA molecules.

Mitotic Phase

Mitosis and cytokinesis (includes Prophase, Metaphase, Anaphase, Telophase)
Prophase: Chromosomes condense and become visible, spindle fibers (microtubules) start to form, the nuclear envelope disintegrates
Metaphase: Chromosomes line up in the middle of the cell, attached to spindle fibers.
Anaphase: Sister chromatids separate and move to opposite poles pulled by spindle fibers.
Telophase: Chromosomes arrive at opposite poles, nuclear envelopes begin to reform, chromosomes decondense, the mitotic spindle breaks down.

Checkpoint Control System

Cell cycle is controlled by STOP and GO chemical signals at critical points.
Signals indicate if key cellular processes have been completed correctly.
G1: checks DNA, growth factors, nutrition, and cell size.
G2: checks if DNA replication is complete and DNA is intact.
M: checks if chromosomes are attached to spindle fibers correctly.

Checkpoints (continued)

G2/M checkpoint: checks DNA replication and integrity.
G1/S checkpoint: regulates the cell cycle by monitoring growth factor signaling and nutritional conditions.
Spindle checkpoint: monitors proper chromosome alignment and attachment of chromosomes to the spindle apparatus.

Checkpoints Control System (continued)

Signals that promote cell growth & division proteins are called "promoting factors," external signals (like growth factors) are external.
Primary mechanisms of control are phosphorylation (adding phosphate) through Kinase enzymes, and dephosphorylation (removing phosphate). Protein phosphorylation and dephosphorylation by kinases and phosphatases are major regulatory steps that control the cell cycle

Cyclin and Cyclin-Dependent Kinases (CDKs)

CDKs and cyclins drive the cell cycle from one phase to the next.
Proper regulation of the cell cycle is crucial for life.
Genes for regulatory proteins are highly conserved through evolution.
The related proteins are similar in yeast, insects, plants, and animals

Meiosis

Meiosis is a specialized type of cell division that occurs in the gonads (ovaries and testes) to form gametes.
Meiosis reduces the chromosome number by half.
Gametes (sperm and egg cells) are haploid (n).
Fertilization restores the diploid (2n) number of chromosomes.

Comparison of Mitosis and Meiosis

Mitosis results in genetically identical cells, while meiosis results in genetically unique gametes.
Mitosis occurs throughout life to aid growth and repair, while meiosis occurs at sexual maturity.
Meiosis has two divisions (I and II), mitosis has one.

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Description

This quiz tests your understanding of protein synthesis and cell division. You will describe the processes of gene expression, transcription, translation, and the stages of cell division. Assess your knowledge of how these processes impact cellular functions.