How do cells grow, specialise & die? Flashcards
What is DNA?
- DNA: deoxyribonucleic acid
- Genetic information contained in nucleus
- Contains genetic information for protein formation
- Approximately 23 000 genes in human genome
- Genes code for proteins
- Only 1.5% of DNA is due to genes
- 98.5% of DNA is non-coding – e.g regulatory sequences, introns, and noncoding DNA – e.g repeat elements
What is the structure of DNA?
-Double-stranded (double helix - twisted ladder)
-Sugar-phosphate backbone
-Complementary nitrogenous bases
o adenine – thymine
o guanine - cytosine
What is the organisation of DNA?
- Double strand of DNA – twisted ladder
- DNA wrapped around proteins called histones.
- Histones & DNA bundled together – chromatin
- Chromatin twists around to make chromosomes
What are maternal & paternal chromosomes
- Each somatic human cell has two copies of each chromosome – one you inherited from Mum and one from Dad.
- The maternal and paternal chromosomes of a pair are called homologous chromosomes (make a “homologous pair)
How many pairs of autosomal & sex chromosomes do humans have?
-Humans have 22 pairs of autosomal chromosomes and 1 pair of sex chromosomes
o Women have 2 X chromosomes and men have an X and Y
In somatic cells & gametes how many chromosomes are there? What happens when cells are dividing?
- Somatic cells with 46 chromosomes (23 pairs) are said to be diploid (have the full amount of DNA)
- Gametes (sperm and egg) only have 1 chromosome of each homologous pair (have 23 chromosomes) and are called haploid (have half the normal amount of DNA)
- When cells are dividing, the chromosomes become easier to see and we can arrange them next to their pair – this kind of map is a karyotype
What is a Karyotype?
A map of chromosomes in dividing cell
Define genetics, gene, allele, genotype & phenotype
Genetics - study of heredity Gene – piece of DNA that codes for a protein Allele – alternative form of a gene Genotype – the actual gene (allele) Phenotype - person’s appearance
What are cells?
- Cells are protein factories that constantly synthesize many different proteins
- These proteins are used for cell functions or can be exported
What do cells DNA contain?
- The cell’s DNA contains all the instructions the cell needs for making proteins
- Not all cells make all proteins – some proteins are needed only by specific cells.
What is the proteome of a cell?
- The “proteome” of a cell is all the proteins that a cell makes, and “proteomics” is the study of the proteins in a cell.
- The proteome of one cell can be compared to another to see how they are different.
- A muscle cell vs a skin cell
- A melanoma vs a normal melanocyte
What is transcription and translation?
- Transcription= DNA > RNA
- Translation= RNA > protein
- Flow of information from DNA to RNA to protein: The Central Dogma
What is transcription?
- DNA has two strands, but only one strand of the DNA is used as a template to make RNA
- Genetic information (a gene) is copied from a strand of DNA to make a strand of ribonucleic acid (RNA) called mRNA (messenger RNA)
RNA is like DNA except?
-RNA is like DNA except – o Sugar: ribose instead of deoxyribose o It is single-stranded o Contains uracil instead of thymine -RNA acts as an intermediary between DNA and protein
What is initiated by transcription & mRNA produced is called what?
- Initiated by transcription factors that recruit RNA polymerase enzyme
- The mRNA produced is called an RNA transcript
What starts and stops a gene?
-There are special sequences/signals in DNA that indicate when a gene starts and stops
What is within a gene & what does the initial mRNA transcript contain?
- Within a gene there are exons (coding) and introns (non-coding)
- The initial mRNA transcript (pre-mRNA) contains both the exons and introns. The RNA introns are then cut out and the exons are all joined together. This transcript is called processed RNA
Name & describe the kinds of RNA transcribed from DNA
-Three kinds of RNA are transcribed from DNA
o Messenger RNA (mRNA): is translated in the cytoplasm to make proteins
o Ribosomal RNA (rRNA): together with ribosomal proteins rRNA makes up the ribosomes
o Transfer RNA (tRNA): each tRNA can bind specifically to one of the 20 different amino acids used to build proteins, important in translating mRNA into amino acid peptide
Describe the events that occur when the DNA strands seperate
-The strands of DNA are separated
-RNA polymerase binds at a promoter region
-RNA polymerase catalyses the formation of a mRNA chain using the DNA as a template and following the rules of complimentary base pairing
o A with U
o C with G
How does transcription end?
- Transcription ends at a terminator sequence
- DNA uncoils and unzips
- RNA polymerase –> messenger RNA (mRNA)
- mRNA exits nucleus through nuclear pores
What does translation do & where does it occur?
-Turns mRNA into a protein
-Occurs in the cytoplasm – by ribosomes
o On rough endoplasmic reticulum (RER)
o Free within cytoplasm
What does mRNA carry?
-mRNA carries genetic information from the nucleus to the ribosomes