week 13: How do cells grow, specialize and die? DNA, protein synthesis and cell division

nucleotide

-pentose sugar; deoxyribose, ribose

-phosphate group

-nitrogenous base; adenine, guanine, cytosine, thymine, uracil

DNA

-Deoxyribonucleic acid

-mainly in nucleus but also in mitochondria

-blueprint codes for protein synthesis

DNA - structure

-double helix

-double stranded polymer; two polynucleotide chains, antiparallel

-alternating sugar phosphate backbone

-nitrogenous bases held together by hydrogen bonds

base pairing rule

adenosine = thymine (A=T)

cytosine = guanine (C=G)

organization of DNA

-double strands of DNA; twisted ladder

-DNA wrapped around proteins called histones

-histones and DNA bundles is called chromatin

-chromatin twist and condense to form chromosomes

-each chromosome contains hundreds to thousands of genes

diploid

somatic cells = 46 chromosomes (23 pairs)

karyotype

-a map of chromosomes in a dividing cell

-male karyotype (22 autosomes + xy)

RNA

-ribo nucleic acid

-single stranded polymer, self complementary sequences forms folds, bulges and helices

-supports DNA during protein synthesis

-found both in the nucleus and cytoplasm

-alternating sugar-phosphate backbone

functions of proteins

-regulation

-transport

-protection

-contraction

-structure

-energy

protein structure - primary

sequence of amino acids linked by peptide bonds

protein structure - secondary

-protein folds to form secondary structures because amino acids have different side chains

-two regular folding patterns: alpha helices (keratin) and beta pleated sheets (fibroin, silk)

protein structure - tertiary

the 3D shape is determined by the folding of the secondary structure. The a-helices and b-sheets fold to form unique structures which are held together by bonds between amino acids that may be far apart in the actual polypeptide chain

protein structure - quaternary

-combined three-dimensional structure of two or more polypeptide chain

fibrous proteins

-simple, elongated polypeptides chains arranged in parallel fashion along a single axis

-are usually insoluble in water and stable

-provide mechanical support and tensile strength, more structure

-less sensitive to changes in temp, pH, etc

globular proteins

-polypeptide chains fold up into a compact shape, like a ball with rough surface

-usually water soluble

-mobile, chemically active

-sensitive to changes in temp, pH, etc

proteome

-proteome of a cell is all the proteins that a cell makes, and proteomics is the study of the proteins in a cell

protein synthesis

the specific arrangement of amino acids determines the shape, properties and functions of the protein

transcription

-occurs in nucleus

-a copy of small part of the stored information in DNA (gene) is produced

-DNA -> mRNA

translation

-occurs in cytoplasm

-copied information is converted into a protein

-mRNA -> protein

transcription - process

-two strands of DNA separate/unzip

-RNA polymerase bind at the promoter region

-genetic information (gene) is copied from the template strand of DNA to make a strand of RNA called mRNA

-mRNA chain follow rules of paring; A=U, C=G

-transcription ends at the terminator sequence

-mRNA exits nucleus through nuclear pores into the cytoplasm

translation - process

-mRNA carries genetic information from the nucleus to the ribosomes

-The sequence is "read" by translational machinery in the ribosome, in lots of three nucleotides (nucleotide triplets = codon)

-Translation starts at the start codon (AUG) of each gene in the mRNA

-Each codon codes for a specific amino acid

-As each codon is read, a tRNA with a complimentary sequence (anticodon) binds to each triplet

-The tRNA also carries the amino acid specified by the codon

-Amino acids are joined together by peptide bonds, in the sequence specified by the mRNA, to make a peptide/protein

post-translational modification

-It is one of the last steps in protein synthesis

-After translation, proteins can be modified by attaching other functional groups which can change or extend its functions • e.g lipids (lipoproteins) carbohydrates (glycoproteins)

-Amino acids may be cleaved off the end of the protein or the polypeptide can be cut in half, e.g. insulin

somatic cells

a biological cell forming the body of a multicellular organism

germ cell

cells that give rise to gametes. located in the gonads - ovaries and testes

gamete

cells that fuse during sexual reproduction sperm or egg (23 chromosomes) haploid number

cell life cycle - interphase

phase between cell division. Ongoing normal cell activities e.g. makes hormones, transmits action positional, contracts. Replication of DNA and preparation for division

cell life cycle - mitosis

series of events that leads to the production of two somatic cells by division of one mother cell into two daughter cells. cells are genetically identical

-prophase

-metaphase

-anaphase

-telophase

cell life cycle - cytokinesis

division of cell cytoplasm

chromatin

-DNA complexed with proteins (histones)

-during cell division, chromatin condenses into pairs of chromatids called chromosomes. each pair of chromatids is joined by centromere

homologous chromosomes

pairs of chromosomes - where one is from the father and the other is from the mother (gametes)

locus chromosomes

the location of the gene on a chromosome

alelle chromosomes

different forms of the same gene

DNA replication - interphase

DNA replication occurs. each chromosomes becomes doubled, consisting of 2 identical strands of the DNA

structure of a mitotic chromosome

1. The DNA of a chromosome is dispersed as chromatin.

2. The DNA molecule unwinds, and each strand of the molecule is replicated.

3. During mitosis, the chromatin from each replicated DNA strand condenses to form a chromatid. The chromatids are joined at the centromere to form a single chromosome.

4. The chromatids separate to form two new, identical chromosomes. The chromosomes will unwind to form chromatin in the nuclei of the two daughter cells.

prophase

chromatin condenses to form chromosomes, centrioles migrate to ends of each, spindle fiber's attached to centromeres, nuclear envelop disintegrates

metaphase

chromosomes are aligned at the nuclear equator

anaphase

spindle fibre's separate the chromatids, 2 identical sets of chromosomes are moved to separate ends of the cell, cytokinesis begins

telophase

nuclear envelope reforms around each set of chromosomes, chromosomes decondense into chromatin, cytokinesis continues

cytokinesis

cytoplasmic division

I.P.M.A.T

-interphase

-prophase

-metaphase

-anaphase

-telophase

homologous crossing-over

prophase 1: homologous chromosomes line up next to each other. DNA is exchange between the adjacent homologous chromatids. Sister chromatid strands of each chromosomes are no longer identical, results in exchange of genetic material between maternal and paternal chromosomes

spermatogenesis

-happens in the gonads

-the testes make gametes (sperm) via meiosis

-4 functional sperm cells per division. non identical 23 chromosomes

-lifelong process in testes

oogenesis

-the ovaries make gametes (oocytes) via meiosis

-at birth the ovaries contain all the oocytes they will ever have - stalled in prophase 1

-1 function oocyte per division, 3 polar bodies, non identical and contains 23 chromosomes

What is the name of the process by which DNA is converted into mRNA and where does this event take place within the cell?

Transcription, which takes place in the cell's nucleus.

How and why does the cell package its DNA ready for division?

DNA condenses to form chromatin, which then winds up to form chromosomes. Packaging the DNA in this way means it is protected during cell division and is easier to divide in half

What is the difference between a protein, a peptide and a polypeptide?

A peptide is a short chain of amino acids. The distinction between peptide vs. polypeptide vs. protein is flexible Generally peptides are 2 or more amino acids, polypeptides are 10 - 50 amino acids long, and proteins are > 50 amino acids long.

What is the relationship of DNA to proteins?

DNA carries the code for the specific sequence of amino acids that form a particular protein

How many nucleic acid bases code for one amino acid?

3, this group of 3 is called a CODON

What is the purpose of the first meiotic division?

Meiosis I separates homologous chromosomes, producing two haploid cells (23 chromosomes) which is half the amount of DNA in a "normal" cell. Thus, meiosis I is referred to as a reductional division

What do you think is the purpose of allowing some 'swapping' of bits of chromatid between members of homologous pairs during meiosis I

It increases genetic variation/variety in humans

After the second meiotic division is completed, are the four haploid cells (i.e. cells with half the number of chromosomes) genetically identical?

Close - but no, the key is in the swapping or crossing over of chromatids

How many alleles for a given gene does a gamete (sex cell) have?

One, because each gamete only has one copy of each chromosome, not two like a somatic (body) cell