Topic 3-Voice of the Genome

What are all living things made up of?

Cells

What are eukaryotic cells?

They’re complex and include animal and plant cells

What are prokaryotic cells?

They’re smaller and simpler and include bacteria

What are organelles?

They’re parts of cells. Each one having a specific function.

What is cell ultrastructure?

The internal structure of cells that are not visible through a light microscope

What organelles do animal (eukaryotic) cells have?

-cell surface membrane

-rough endoplasmic reticulum

-nucleolus

-centriole

-nucleus

-smooth endoplasmic reticulum

-lysosome

-ribosome

-nuclear envelope

-Golgi apparatus

-cytoplasm

-mitochondria

Describe the nucleus

-surrounded by a nuclear envelope (double membrane) containing pores

-contains chromatin and the nucleolus

Describe the function of the nucleus

-controls the cells activities by controlling transcription

-DNA contains instructions to make proteins

-pores allow substances to move between the nucleus and the cytoplasm

-nucleolus makes ribosomes

Describe the lysosome

-round organelle

-surrounded by a membrane

-no clear internal structure

Describe the function of the lysosome

-contains digestive enzymes

-used to digest invading cells or to break down worn out components of the cell

Describe the ribosome

-very small

-floats free in the cytoplasm or is attached to the rough endoplasmic reticulum

-made of proteins and RNA

-not surrounded by a membrane

Describe the function of the ribosome

-where proteins are made

Describe the rough endoplasmic reticulum

-system of membranes enclosing a fluid filled space

-c surface covered with ribosomes

Describe the function of rough endoplasmic reticulum

-folds and processes proteins that have been made at the ribosomes

Describe the smooth endoplasmic reticulum

-has no ribosomes

Describe the purpose of the smooth endoplasmic reticulum

-synthesises and processes lipids

Describe the Golgi apparatus

-group of fluid filled membrane bound flattened sacs

-vesicles are seen at the edges of the sacs

Describe the function of Golgi apparatus

-processes and packages new lipids and proteins

-makes lysosomes

Describe the mitochondrion

-oval shaped

-double membrane

-inner layer of folded to form cristae

-the matrix contains enzymes involved in respiration

Describe the function of the mitochondrion

-site of aerobic respiration where ATP is produced

-found in cells that are active and require a lot of energy

Describe the centriole

-small, hollow cylinders made of microtubules

-found in animal cells and only some plant cells

Describe the function of the centriole

-involved with the separation of chromosomes during cell division

Describe how the rough endoplasmic reticulum and Golgi apparatus are involved in proteins production and transport

1. A region of DNA corresponding to a gene is transcribed in the nucleus, producing mRNA

2. mRNA binds a ribosome on the RER and is translated, producing a polypeptide that adopts its tertiary structure in the RER

3. A transport vesicle containing the protein pinches off the RER and fuses with the Golgi apparatus

4. In the Golgi, the protein is modified and packaged into a secretory vesicle that moves to and fuses with its destination

5. For example a secreted protein (such as an antibody or extracellular enzyme) will be in a vesicle that will undergo exocytosis

How prokaryotic cells organelle slightly different than eukaryotic cells?

-cytoplasm lacks membrane bound organelles

-ribosomes are smaller

-have a single bacterial chromosome

-has a cell wall containing glycoprotein Murien/peptidoglycan

What additional structures do prokaryotic cells have?

-plasmids

-capsules

-flagella

-pili

-mesosomes

What is the purpose of plasmids?

-small loops of DNA that are separate from the main circular DNA molecule

-contains genes that can be passed between prokaryotes

Describe the purpose of capsules

-surrounded by outer layer

-helps protect bacteria from drying out and from attack by cells of the immune system of the host organism

What a the purpose of the flagellum

-long, hair like structure that rotates enabling the prokaryote to move

What is the purpose of the pili?

-thread like structures

-enable bacteria to attach to other cells or surfaces

Describe the purpose of mesosomes

-infolded regions in the plasma membrane of some prokaryotic cells

-aerobic respiration, cell wall formation and DNA replication

Describe the purpose of circular DNA

-single circular strand of genetic material not contained in a membrane bound nucleus

-this molecule is found in the nucleoid

Describe the purpose of ribosomes

-smaller than eukaryotic ribosomes-70S

-site of protein synthesis

What are gametes?

Sex cells

What does fertilisation form?

Zygote

How many chromosomes are in one gamete?

23

What does fertilisation describe?

The exact moment when the nuclei of the male and female gametes fuse

What does combining genetic materials from two individuals form?

Genetically unique offspring

What do egg and sperm cells have the same organelles as?

Eukaryotic cells

Describe how the egg cell is specialised for its function

-Haploid nuclear

-cell plasma membrane

-follicle cells=form a protective coating

-zona pellucida=forms an impenetrable barrier after fertilisation, preventing other sperm from entering the cell

-lipid droplets

-contains food to provide energy for the dividing zygote

Describe how the sperm cell is specialised for its function

-haploid nucleus

-cell plasma membrane

-acrosome=contains digestive enzymes to break down the eggs zona pellucida and enable to sperm to penetrate the egg

-mitochondria=provide energy for tail movement

-flagellum=allows sperm to swim towards egg cell

Where does fertilisation in mammals occur?

Oviduct

Describe the process of fertilisation

1. Sperm reaches ovum attracted by chemicals released by ovum and the chemical released from the follicle cells trigger the acrosome reaction

2. Acrosome membrane fuses with front of sperm cell membrane. Digestive enzymes in acrosome are released by exocytosis

3. Digestive enzymes digest the zona pellucida. Acrosome all process forms and binds to receptors on egg cell membrane

4. Sperm cell membrane fuses with the ovum membrane

5. Sperm nucleus enters the ovum and the cortical reaction is triggered

6. Cortical enzymes released from the ovum cause the zona pellucida to form a tough layer which prevents entry of any other sperm and sperm binding receptors are clipped from the egg cell membrane

7. Nuclei of sperm and ovum fuse, the egg is fertilised and a diploid zygote is formed

What is genetic variation?

The differences that exist between individuals genetic material

1. Describe the crossing over of chromatids

1. Homologous pairs of chromosomes come together and pair up

2. Two of the chromatids in each homologous pair twist around each other

3. Twisted bits break off their original chromatid and rejoin onto the other chromatid, recombining their genetic material

4. chromatids still contain the same genes but they have a different combination of alleles

5. Meaning each of the 4 new cells formed from meiosis contains chromatids with different alleles

Describe the independent assortment of chromosomes

1. Four daughter cells formed from meiosis have a completely different combinations of chromosomes

2. All cells have a combination of chromosomes from your parents

3. When gametes are produced different combinations of maternal and paternal chromosomes go into each cell

4. Called independent assortment

What is a locus?

The position of a gene on a chromosome

What does independent assortment mean for genes with loci on different chromosomes?

They’re randomly distributed in gametes

What are genes with loci on the same chromosome said to be and why?

-linked

-because they’ll stay together during independent assortment and their alleles will be passed on to the offspring together

How do you know two genes are closely linked?

They’re closer together and crossing over is less likely to split them up

When is a characteristic said to be sex linked?

When the locus of the allele that codes for it is on a sex chromosome

Why does the Y chromosome carry fewer genes And what does this cause?

It’s smaller and causes most genes are carried on the X chromosome (X-linked)

Why are males likely to express the characteristic if it’s sex linked?

They only have one X chromosome and so only one copy of the gene so it show even if it’s recessive

What are some genetic disorders caused by faulty alleles and what chromosome are the carried on?

Colour blindness and haemophilia and they’re carried on the X chromosome (X linked disorders)

What a meiosis?

A type of cell division that occurs in reproductive organs to form gametes

Describe the process of meiosis

1. DNA replicates to form 2 identical copies of each chromosome, called chromatids.

2. DNA condenses to form double armed chromosomes, from 2 sister chromatids.

3. Chromosomes arrange themselves into homologous pairs.

4. FIRST DIVISION-homologous pairs are separated, halving the chromosome number.

5. SECOND DIVISION-pairs of sister chromatids are separated.

6. Four new daughter cells which are genetically different from each other are formed (gametes).

What does mitosis produce?

Genetically identical cells

What is mitosis needed for?

• Growth

• Repair

• Asexual reproduction

What is the order of events in the cell cycle?

• Cell growth

• Interphase

• Mitosis

Describe the process of Interphase

1. Cells DNA is unraveled and replicated, to double its genetic content

2. Organelles are replicated

3. ATP content is increased

What are the 4 stages of mitosis?

• Prophase

• Metaphase

• Anaphase

• Telophase

Describe Prophase

• Chromosomes condense, getting shorter and fatter

• Centrioles move to opposite poles of the cells, forming spindle fibres

• Nuclear envelope breaks down and chromosomes lie free in the cytoplasm

Describe Metaphase

• Chromosomes, each with 2 chromatids, line up along the equator of the cell

• Spindle fibres attach to the centromere

Describe Anaphase

• Centromeres divide, separating each pair of sister chromatids

• Spindles contract, pulling chromatids to opposite poles of the spindle centromere first

• Chromatids appear v-shaped

Describe Telophase

• Chromatids reach the opposite poles of the spindle

• They uncoil and become long and thin again

• Nuclear envelope forms around each chromosome, so there are two nuclei

• Cytoplasm divides (cytokinesis) and there are two daughter cells that are genetically identical to the original cell to each other.

• Mitosis is finished and each daughter cell starts the interphase part of the cell cycle to get ready for the next round of mitosis

What are stem cells?

Unspecialised cells that can develop into other types of cells

What is differentiation?

The process of cells becoming specialised

What does potency mean?

The ability of stem cells to differentiate into specialised cells

Define Totipotency

The ability to produce all types of cells, including all specialised cells in an organism and extraembryonic cells.

Define Pluripotency

The ability of a stem cell to produce all the specialised cells in an organism, but not extraembryonic cells.

When are totipotent stem cells present?

During the first few cell divisions of an embryo

Why do stem cells become specialised?

Different genes in the DNA become active and are expressed

Describe the process of differential gene expression

1. Some stem cell genes aren’t expressed because they’re not active

2. Under the right conditions, some genes are activated and others are deactivated.

3. mRNA is only transcribed from active genes.

4. mRNA from active genes is translated into proteins.

5. Proteins modify the cells and determine their structure and control cell processes

6. Changes to the cell produced by proteins cause the cell to become specialised. Changes are difficult to reverse so the cell stays specialised.

What controls gene expression and how does it do it?

Transcription factors- proteins bind to DNA and activate or deactivate genes by increasing or decreasing the rate of transcription

What factors increase the rate of transcription and how does it do it?

Activators-help RNA polymerase bind to the DNA and begin transcription

What factors decrease the rate of transcription and how does it do this?

Repressors- work by preventing RNA polymerase from binding to DNA stopping transcription

What is an operon?

Section of DNA that contains a cluster of structural genes, that are transcribed together, as well as control elements and sometimes a regulatory gene.

What do structural genes code for?

Useful proteins like enzymes

What do control elements include?

A promoter and and operator

What does the regulatory gene code for?

An activator or repressor

What does the E.Coli bacterium respire and what does it use if there is not enough of that?

-respires glucose but can use lactose

Where are the genes that produce enzymes in order to respire glucose found?

On the lac operon

What are the 3 structural genes on the lac operon and what do they do?

-lacZ, lacY, lacA

-produce proteins that help bacteria digest lactose

Describe what happens on the lac operon when lactose is not present

-regulatory gene produces the lac repressor, which is a transcription factor that binds to the operator site when there’s no lactose present.

-this blocks transcription as RNA polymerase can’t bind to the promoter

Describe what happens of the lac operon when lactose is present

-lactose binds to the repressor, changing the repressors shape so that it can no longer bind to the operator site.

-RNA polymerase can now begin transcription of the structural genes

What is a tissue?

Group of similar cells that are specially adapted to work together to carry out a particular function.

What is an organ?

Group of different tissues that work together to perform a particular function.

What is an organ system?

Group of organs working together for a particular function.

What conditions can stem cell treatments be used for?

• Spinal cord injuries

• Heart disease and damage caused by heart attacks

What are the potential benefits of stem cell therapies?

• Saves many lives-eg.used to grow organs

• Improves the quality of life of people-eg.replacing damaged cells of people blind people

Describe adults stem cells

• Obtained from body tissues eg. Bone marrow.

• Little risk but lots of discomfort.

• Can only differentiate into a limited range of cells.

• Less risk of rejection if the stem cells are taken from the patient.

Describe embryonic stem cells

• Obtained from early embryos

• Embryos are created through IVF

• Stem cells are removed from them and the rest are destroyed.

• Can develop into all types of specialised cells.

Ethical objections of embryonic stem cells

• Results in the destruction of an embryo that is viable

• Embryo has a right to life

• Wrong to destroy an embryo

Why do people agree with using embryonic stem cells?

• People believe the embryo wouldn’t survive in the womb

• Embryonic stem cells can develop into more specialised cells

Describe the work of regulatory authorities which consider the benefits and ethical issues of embryonic stem cell research

1. Looking at proposals of research and deciding if they should be allowed by taking ethical issues into account-ensures research is carried out for a good reason.

2. Licensing and monitoring centres-ensure fully trained staff carry out the research and won’t waste precious resources.

3. Producing guidelines and codes of practise-ensures all scientists are working in a similar manner.

4. Monitoring developments in scientific research and advances- ensures any changes in the field are regulated appropriately.

5. Providing information and advance to governments and professionals- helps promote the science involved in embryo research.

What is continuous variation?

When the individuals in a population vary within a range with no distinct categories.

What is discontinuous variation?

When there are two or more distinct categories-each individual falls into only one of these categories

Define mono genetic

Characteristics controlled by one gene

Define polygenetic

Characteristics controlled by a number of genes at different loci

Describe a characteristic that the environment impacts to produce the phenotype

Height:

• Impacted by nutrition

• Tall parents usually have tall children but undernourished children won’t grow to their maximum height.

How does epigenetic control work?

Attaches or removes chemical groups to or from the DNA.

This alters how easy it is for the enzymes and other proteins needed for transcription to interact with and transcribe genes.